fs/ext4/mballoc.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2003-2006, Cluster File Systems, Inc, info@clusterfs.com
 * Written by Alex Tomas <alex@clusterfs.com>
 */


/*
 * mballoc.c contains the multiblocks allocation routines
 */

#include "ext4_jbd2.h"
#include "mballoc.h"
#include <linux/log2.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/nospec.h>
#include <linux/backing-dev.h>
#include <linux/freezer.h>
#include <trace/events/ext4.h>
#include <kunit/static_stub.h>

/*
 * MUSTDO:
 *   - test ext4_ext_search_left() and ext4_ext_search_right()
 *   - search for metadata in few groups
 *
 * TODO v4:
 *   - normalization should take into account whether file is still open
 *   - discard preallocations if no free space left (policy?)
 *   - don't normalize tails
 *   - quota
 *   - reservation for superuser
 *
 * TODO v3:
 *   - bitmap read-ahead (proposed by Oleg Drokin aka green)
 *   - track min/max extents in each group for better group selection
 *   - mb_mark_used() may allocate chunk right after splitting buddy
 *   - tree of groups sorted by number of free blocks
 *   - error handling
 */

/*
 * The allocation request involve request for multiple number of blocks
 * near to the goal(block) value specified.
 *
 * During initialization phase of the allocator we decide to use the
 * group preallocation or inode preallocation depending on the size of
 * the file. The size of the file could be the resulting file size we
 * would have after allocation, or the current file size, which ever
 * is larger. If the size is less than sbi->s_mb_stream_request we
 * select to use the group preallocation. The default value of
 * s_mb_stream_request is 16 blocks. This can also be tuned via
 * /sys/fs/ext4/<partition>/mb_stream_req. The value is represented in
 * terms of number of blocks.
 *
 * The main motivation for having small file use group preallocation is to
 * ensure that we have small files closer together on the disk.
 *
 * First stage the allocator looks at the inode prealloc list,
 * ext4_inode_info->i_prealloc_list, which contains list of prealloc
 * spaces for this particular inode. The inode prealloc space is
 * represented as:
 *
 * pa_lstart -> the logical start block for this prealloc space
 * pa_pstart -> the physical start block for this prealloc space
 * pa_len    -> length for this prealloc space (in clusters)
 * pa_free   ->  free space available in this prealloc space (in clusters)
 *
 * The inode preallocation space is used looking at the _logical_ start
 * block. If only the logical file block falls within the range of prealloc
 * space we will consume the particular prealloc space. This makes sure that
 * we have contiguous physical blocks representing the file blocks
 *
 * The important thing to be noted in case of inode prealloc space is that
 * we don't modify the values associated to inode prealloc space except
 * pa_free.
 *
 * If we are not able to find blocks in the inode prealloc space and if we
 * have the group allocation flag set then we look at the locality group
 * prealloc space. These are per CPU prealloc list represented as
 *
 * ext4_sb_info.s_locality_groups[smp_processor_id()]
 *
 * The reason for having a per cpu locality group is to reduce the contention
 * between CPUs. It is possible to get scheduled at this point.
 *
 * The locality group prealloc space is used looking at whether we have
 * enough free space (pa_free) within the prealloc space.
 *
 * If we can't allocate blocks via inode prealloc or/and locality group
 * prealloc then we look at the buddy cache. The buddy cache is represented
 * by ext4_sb_info.s_buddy_cache (struct inode) whose file offset gets
 * mapped to the buddy and bitmap information regarding different
 * groups. The buddy information is attached to buddy cache inode so that
 * we can access them through the page cache. The information regarding
 * each group is loaded via ext4_mb_load_buddy.  The information involve
 * block bitmap and buddy information. The information are stored in the
 * inode as:
 *
 *  {                        page                        }
 *  [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.  So for each group we
 * take up 2 blocks. A page can contain blocks_per_page (PAGE_SIZE /
 * blocksize) blocks.  So it can have information regarding groups_per_page
 * which is blocks_per_page/2
 *
 * The buddy cache inode is not stored on disk. The inode is thrown
 * away when the filesystem is unmounted.
 *
 * We look for count number of blocks in the buddy cache. If we were able
 * to locate that many free blocks we return with additional information
 * regarding rest of the contiguous physical block available
 *
 * Before allocating blocks via buddy cache we normalize the request
 * blocks. This ensure we ask for more blocks that we needed. The extra
 * blocks that we get after allocation is added to the respective prealloc
 * list. In case of inode preallocation we follow a list of heuristics
 * based on file size. This can be found in ext4_mb_normalize_request. If
 * we are doing a group prealloc we try to normalize the request to
 * sbi->s_mb_group_prealloc.  The default value of s_mb_group_prealloc is
 * dependent on the cluster size; for non-bigalloc file systems, it is
 * 512 blocks. This can be tuned via
 * /sys/fs/ext4/<partition>/mb_group_prealloc. The value is represented in
 * terms of number of blocks. If we have mounted the file system with -O
 * stripe=<value> option the group prealloc request is normalized to the
 * smallest multiple of the stripe value (sbi->s_stripe) which is
 * greater than the default mb_group_prealloc.
 *
 * If "mb_optimize_scan" mount option is set, we maintain in memory group info
 * structures in two data structures:
 *
 * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
 *
 *    Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
 *
 *    This is an array of lists where the index in the array represents the
 *    largest free order in the buddy bitmap of the participating group infos of
 *    that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
 *    number of buddy bitmap orders possible) number of lists. Group-infos are
 *    placed in appropriate lists.
 *
 * 2) Average fragment size lists (sbi->s_mb_avg_fragment_size)
 *
 *    Locking: sbi->s_mb_avg_fragment_size_locks(array of rw locks)
 *
 *    This is an array of lists where in the i-th list there are groups with
 *    average fragment size >= 2^i and < 2^(i+1). The average fragment size
 *    is computed as ext4_group_info->bb_free / ext4_group_info->bb_fragments.
 *    Note that we don't bother with a special list for completely empty groups
 *    so we only have MB_NUM_ORDERS(sb) lists.
 *
 * When "mb_optimize_scan" mount option is set, mballoc consults the above data
 * structures to decide the order in which groups are to be traversed for
 * fulfilling an allocation request.
 *
 * At CR_POWER2_ALIGNED , we look for groups which have the largest_free_order
 * >= the order of the request. We directly look at the largest free order list
 * in the data structure (1) above where largest_free_order = order of the
 * request. If that list is empty, we look at remaining list in the increasing
 * order of largest_free_order. This allows us to perform CR_POWER2_ALIGNED
 * lookup in O(1) time.
 *
 * At CR_GOAL_LEN_FAST, we only consider groups where
 * average fragment size > request size. So, we lookup a group which has average
 * fragment size just above or equal to request size using our average fragment
 * size group lists (data structure 2) in O(1) time.
 *
 * At CR_BEST_AVAIL_LEN, we aim to optimize allocations which can't be satisfied
 * in CR_GOAL_LEN_FAST. The fact that we couldn't find a group in
 * CR_GOAL_LEN_FAST suggests that there is no BG that has avg
 * fragment size > goal length. So before falling to the slower
 * CR_GOAL_LEN_SLOW, in CR_BEST_AVAIL_LEN we proactively trim goal length and
 * then use the same fragment lists as CR_GOAL_LEN_FAST to find a BG with a big
 * enough average fragment size. This increases the chances of finding a
 * suitable block group in O(1) time and results in faster allocation at the
 * cost of reduced size of allocation.
 *
 * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
 * linear order which requires O(N) search time for each CR_POWER2_ALIGNED and
 * CR_GOAL_LEN_FAST phase.
 *
 * The regular allocator (using the buddy cache) supports a few tunables.
 *
 * /sys/fs/ext4/<partition>/mb_min_to_scan
 * /sys/fs/ext4/<partition>/mb_max_to_scan
 * /sys/fs/ext4/<partition>/mb_order2_req
 * /sys/fs/ext4/<partition>/mb_linear_limit
 *
 * The regular allocator uses buddy scan only if the request len is power of
 * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
 * value of s_mb_order2_reqs can be tuned via
 * /sys/fs/ext4/<partition>/mb_order2_req.  If the request len is equal to
 * stripe size (sbi->s_stripe), we try to search for contiguous block in
 * stripe size. This should result in better allocation on RAID setups. If
 * not, we search in the specific group using bitmap for best extents. The
 * tunable min_to_scan and max_to_scan control the behaviour here.
 * min_to_scan indicate how long the mballoc __must__ look for a best
 * extent and max_to_scan indicates how long the mballoc __can__ look for a
 * best extent in the found extents. Searching for the blocks starts with
 * the group specified as the goal value in allocation context via
 * ac_g_ex. Each group is first checked based on the criteria whether it
 * can be used for allocation. ext4_mb_good_group explains how the groups are
 * checked.
 *
 * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
 * get traversed linearly. That may result in subsequent allocations being not
 * close to each other. And so, the underlying device may get filled up in a
 * non-linear fashion. While that may not matter on non-rotational devices, for
 * rotational devices that may result in higher seek times. "mb_linear_limit"
 * tells mballoc how many groups mballoc should search linearly before
 * performing consulting above data structures for more efficient lookups. For
 * non rotational devices, this value defaults to 0 and for rotational devices
 * this is set to MB_DEFAULT_LINEAR_LIMIT.
 *
 * Both the prealloc space are getting populated as above. So for the first
 * request we will hit the buddy cache which will result in this prealloc
 * space getting filled. The prealloc space is then later used for the
 * subsequent request.
 */

/*
 * mballoc operates on the following data:
 *  - on-disk bitmap
 *  - in-core buddy (actually includes buddy and bitmap)
 *  - preallocation descriptors (PAs)
 *
 * there are two types of preallocations:
 *  - inode
 *    assiged to specific inode and can be used for this inode only.
 *    it describes part of inode's space preallocated to specific
 *    physical blocks. any block from that preallocated can be used
 *    independent. the descriptor just tracks number of blocks left
 *    unused. so, before taking some block from descriptor, one must
 *    make sure corresponded logical block isn't allocated yet. this
 *    also means that freeing any block within descriptor's range
 *    must discard all preallocated blocks.
 *  - locality group
 *    assigned to specific locality group which does not translate to
 *    permanent set of inodes: inode can join and leave group. space
 *    from this type of preallocation can be used for any inode. thus
 *    it's consumed from the beginning to the end.
 *
 * relation between them can be expressed as:
 *    in-core buddy = on-disk bitmap + preallocation descriptors
 *
 * this mean blocks mballoc considers used are:
 *  - allocated blocks (persistent)
 *  - preallocated blocks (non-persistent)
 *
 * consistency in mballoc world means that at any time a block is either
 * free or used in ALL structures. notice: "any time" should not be read
 * literally -- time is discrete and delimited by locks.
 *
 *  to keep it simple, we don't use block numbers, instead we count number of
 *  blocks: how many blocks marked used/free in on-disk bitmap, buddy and PA.
 *
 * all operations can be expressed as:
 *  - init buddy:			buddy = on-disk + PAs
 *  - new PA:				buddy += N; PA = N
 *  - use inode PA:			on-disk += N; PA -= N
 *  - discard inode PA			buddy -= on-disk - PA; PA = 0
 *  - use locality group PA		on-disk += N; PA -= N
 *  - discard locality group PA		buddy -= PA; PA = 0
 *  note: 'buddy -= on-disk - PA' is used to show that on-disk bitmap
 *        is used in real operation because we can't know actual used
 *        bits from PA, only from on-disk bitmap
 *
 * if we follow this strict logic, then all operations above should be atomic.
 * given some of them can block, we'd have to use something like semaphores
 * killing performance on high-end SMP hardware. let's try to relax it using
 * the following knowledge:
 *  1) if buddy is referenced, it's already initialized
 *  2) while block is used in buddy and the buddy is referenced,
 *     nobody can re-allocate that block
 *  3) we work on bitmaps and '+' actually means 'set bits'. if on-disk has
 *     bit set and PA claims same block, it's OK. IOW, one can set bit in
 *     on-disk bitmap if buddy has same bit set or/and PA covers corresponded
 *     block
 *
 * so, now we're building a concurrency table:
 *  - init buddy vs.
 *    - new PA
 *      blocks for PA are allocated in the buddy, buddy must be referenced
 *      until PA is linked to allocation group to avoid concurrent buddy init
 *    - use inode PA
 *      we need to make sure that either on-disk bitmap or PA has uptodate data
 *      given (3) we care that PA-=N operation doesn't interfere with init
 *    - discard inode PA
 *      the simplest way would be to have buddy initialized by the discard
 *    - use locality group PA
 *      again PA-=N must be serialized with init
 *    - discard locality group PA
 *      the simplest way would be to have buddy initialized by the discard
 *  - new PA vs.
 *    - use inode PA
 *      i_data_sem serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      some mutex should serialize them
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *  - use inode PA
 *    - use inode PA
 *      i_data_sem or another mutex should serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      nothing wrong here -- they're different PAs covering different blocks
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *
 * now we're ready to make few consequences:
 *  - PA is referenced and while it is no discard is possible
 *  - PA is referenced until block isn't marked in on-disk bitmap
 *  - PA changes only after on-disk bitmap
 *  - discard must not compete with init. either init is done before
 *    any discard or they're serialized somehow
 *  - buddy init as sum of on-disk bitmap and PAs is done atomically
 *
 * a special case when we've used PA to emptiness. no need to modify buddy
 * in this case, but we should care about concurrent init
 *
 */

 /*
 * Logic in few words:
 *
 *  - allocation:
 *    load group
 *    find blocks
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - use preallocation:
 *    find proper PA (per-inode or group)
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *    release PA
 *
 *  - free:
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - discard preallocations in group:
 *    mark PAs deleted
 *    move them onto local list
 *    load on-disk bitmap
 *    load group
 *    remove PA from object (inode or locality group)
 *    mark free blocks in-core
 *
 *  - discard inode's preallocations:
 */

/*
 * Locking rules
 *
 * Locks:
 *  - bitlock on a group	(group)
 *  - object (inode/locality)	(object)
 *  - per-pa lock		(pa)
 *  - cr_power2_aligned lists lock	(cr_power2_aligned)
 *  - cr_goal_len_fast lists lock	(cr_goal_len_fast)
 *
 * Paths:
 *  - new pa
 *    object
 *    group
 *
 *  - find and use pa:
 *    pa
 *
 *  - release consumed pa:
 *    pa
 *    group
 *    object
 *
 *  - generate in-core bitmap:
 *    group
 *        pa
 *
 *  - discard all for given object (inode, locality group):
 *    object
 *        pa
 *    group
 *
 *  - discard all for given group:
 *    group
 *        pa
 *    group
 *        object
 *
 *  - allocation path (ext4_mb_regular_allocator)
 *    group
 *    cr_power2_aligned/cr_goal_len_fast
 */
static struct kmem_cache *ext4_pspace_cachep;
static struct kmem_cache *ext4_ac_cachep;
static struct kmem_cache *ext4_free_data_cachep;

/* We create slab caches for groupinfo data structures based on the
 * superblock block size.  There will be one per mounted filesystem for
 * each unique s_blocksize_bits */
#define NR_GRPINFO_CACHES 8
static struct kmem_cache *ext4_groupinfo_caches[NR_GRPINFO_CACHES];

static const char * const ext4_groupinfo_slab_names[NR_GRPINFO_CACHES] = {
	"ext4_groupinfo_1k", "ext4_groupinfo_2k", "ext4_groupinfo_4k",
	"ext4_groupinfo_8k", "ext4_groupinfo_16k", "ext4_groupinfo_32k",
	"ext4_groupinfo_64k", "ext4_groupinfo_128k"
};

static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
					ext4_group_t group);
static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);

static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
			       ext4_group_t group, enum criteria cr);

static int ext4_try_to_trim_range(struct super_block *sb,
		struct ext4_buddy *e4b, ext4_grpblk_t start,
		ext4_grpblk_t max, ext4_grpblk_t minblocks);

/*
 * The algorithm using this percpu seq counter goes below:
 * 1. We sample the percpu discard_pa_seq counter before trying for block
 *    allocation in ext4_mb_new_blocks().
 * 2. We increment this percpu discard_pa_seq counter when we either allocate
 *    or free these blocks i.e. while marking those blocks as used/free in
 *    mb_mark_used()/mb_free_blocks().
 * 3. We also increment this percpu seq counter when we successfully identify
 *    that the bb_prealloc_list is not empty and hence proceed for discarding
 *    of those PAs inside ext4_mb_discard_group_preallocations().
 *
 * Now to make sure that the regular fast path of block allocation is not
 * affected, as a small optimization we only sample the percpu seq counter
 * on that cpu. Only when the block allocation fails and when freed blocks
 * found were 0, that is when we sample percpu seq counter for all cpus using
 * below function ext4_get_discard_pa_seq_sum(). This happens after making
 * sure that all the PAs on grp->bb_prealloc_list got freed or if it's empty.
 */
static DEFINE_PER_CPU(u64, discard_pa_seq);
static inline u64 ext4_get_discard_pa_seq_sum(void)
{
	int __cpu;
	u64 __seq = 0;

	for_each_possible_cpu(__cpu)
		__seq += per_cpu(discard_pa_seq, __cpu);
	return __seq;
}

static inline void *mb_correct_addr_and_bit(int *bit, void *addr)
{
#if BITS_PER_LONG == 64
	*bit += ((unsigned long) addr & 7UL) << 3;
	addr = (void *) ((unsigned long) addr & ~7UL);
#elif BITS_PER_LONG == 32
	*bit += ((unsigned long) addr & 3UL) << 3;
	addr = (void *) ((unsigned long) addr & ~3UL);
#else
#error "how many bits you are?!"
#endif
	return addr;
}

static inline int mb_test_bit(int bit, void *addr)
{
	/*
	 * ext4_test_bit on architecture like powerpc
	 * needs unsigned long aligned address
	 */
	addr = mb_correct_addr_and_bit(&bit, addr);
	return ext4_test_bit(bit, addr);
}

static inline void mb_set_bit(int bit, void *addr)
{
	addr = mb_correct_addr_and_bit(&bit, addr);
	ext4_set_bit(bit, addr);
}

static inline void mb_clear_bit(int bit, void *addr)
{
	addr = mb_correct_addr_and_bit(&bit, addr);
	ext4_clear_bit(bit, addr);
}

static inline int mb_test_and_clear_bit(int bit, void *addr)
{
	addr = mb_correct_addr_and_bit(&bit, addr);
	return ext4_test_and_clear_bit(bit, addr);
}

static inline int mb_find_next_zero_bit(void *addr, int max, int start)
{
	int fix = 0, ret, tmpmax;
	addr = mb_correct_addr_and_bit(&fix, addr);
	tmpmax = max + fix;
	start += fix;

	ret = ext4_find_next_zero_bit(addr, tmpmax, start) - fix;
	if (ret > max)
		return max;
	return ret;
}

static inline int mb_find_next_bit(void *addr, int max, int start)
{
	int fix = 0, ret, tmpmax;
	addr = mb_correct_addr_and_bit(&fix, addr);
	tmpmax = max + fix;
	start += fix;

	ret = ext4_find_next_bit(addr, tmpmax, start) - fix;
	if (ret > max)
		return max;
	return ret;
}

static void *mb_find_buddy(struct ext4_buddy *e4b, int order, int *max)
{
	char *bb;

	BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
	BUG_ON(max == NULL);

	if (order > e4b->bd_blkbits + 1) {
		*max = 0;
		return NULL;
	}

	/* at order 0 we see each particular block */
	if (order == 0) {
		*max = 1 << (e4b->bd_blkbits + 3);
		return e4b->bd_bitmap;
	}

	bb = e4b->bd_buddy + EXT4_SB(e4b->bd_sb)->s_mb_offsets[order];
	*max = EXT4_SB(e4b->bd_sb)->s_mb_maxs[order];

	return bb;
}

#ifdef DOUBLE_CHECK
static void mb_free_blocks_double(struct inode *inode, struct ext4_buddy *e4b,
			   int first, int count)
{
	int i;
	struct super_block *sb = e4b->bd_sb;

	if (unlikely(e4b->bd_info->bb_bitmap == NULL))
		return;
	assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
	for (i = 0; i < count; i++) {
		if (!mb_test_bit(first + i, e4b->bd_info->bb_bitmap)) {
			ext4_fsblk_t blocknr;

			blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
			blocknr += EXT4_C2B(EXT4_SB(sb), first + i);
			ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
					EXT4_GROUP_INFO_BBITMAP_CORRUPT);
			ext4_grp_locked_error(sb, e4b->bd_group,
					      inode ? inode->i_ino : 0,
					      blocknr,
					      "freeing block already freed "
					      "(bit %u)",
					      first + i);
		}
		mb_clear_bit(first + i, e4b->bd_info->bb_bitmap);
	}
}

static void mb_mark_used_double(struct ext4_buddy *e4b, int first, int count)
{
	int i;

	if (unlikely(e4b->bd_info->bb_bitmap == NULL))
		return;
	assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
	for (i = 0; i < count; i++) {
		BUG_ON(mb_test_bit(first + i, e4b->bd_info->bb_bitmap));
		mb_set_bit(first + i, e4b->bd_info->bb_bitmap);
	}
}

static void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
	if (unlikely(e4b->bd_info->bb_bitmap == NULL))
		return;
	if (memcmp(e4b->bd_info->bb_bitmap, bitmap, e4b->bd_sb->s_blocksize)) {
		unsigned char *b1, *b2;
		int i;
		b1 = (unsigned char *) e4b->bd_info->bb_bitmap;
		b2 = (unsigned char *) bitmap;
		for (i = 0; i < e4b->bd_sb->s_blocksize; i++) {
			if (b1[i] != b2[i]) {
				ext4_msg(e4b->bd_sb, KERN_ERR,
					 "corruption in group %u "
					 "at byte %u(%u): %x in copy != %x "
					 "on disk/prealloc",
					 e4b->bd_group, i, i * 8, b1[i], b2[i]);
				BUG();
			}
		}
	}
}

static void mb_group_bb_bitmap_alloc(struct super_block *sb,
			struct ext4_group_info *grp, ext4_group_t group)
{
	struct buffer_head *bh;

	grp->bb_bitmap = kmalloc(sb->s_blocksize, GFP_NOFS);
	if (!grp->bb_bitmap)
		return;

	bh = ext4_read_block_bitmap(sb, group);
	if (IS_ERR_OR_NULL(bh)) {
		kfree(grp->bb_bitmap);
		grp->bb_bitmap = NULL;
		return;
	}

	memcpy(grp->bb_bitmap, bh->b_data, sb->s_blocksize);
	put_bh(bh);
}

static void mb_group_bb_bitmap_free(struct ext4_group_info *grp)
{
	kfree(grp->bb_bitmap);
}

#else
static inline void mb_free_blocks_double(struct inode *inode,
				struct ext4_buddy *e4b, int first, int count)
{
	return;
}
static inline void mb_mark_used_double(struct ext4_buddy *e4b,
						int first, int count)
{
	return;
}
static inline void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
	return;
}

static inline void mb_group_bb_bitmap_alloc(struct super_block *sb,
			struct ext4_group_info *grp, ext4_group_t group)
{
	return;
}

static inline void mb_group_bb_bitmap_free(struct ext4_group_info *grp)
{
	return;
}
#endif

#ifdef AGGRESSIVE_CHECK

#define MB_CHECK_ASSERT(assert)						\
do {									\
	if (!(assert)) {						\
		printk(KERN_EMERG					\
			"Assertion failure in %s() at %s:%d: \"%s\"\n",	\
			function, file, line, # assert);		\
		BUG();							\
	}								\
} while (0)

static void __mb_check_buddy(struct ext4_buddy *e4b, char *file,
				const char *function, int line)
{
	struct super_block *sb = e4b->bd_sb;
	int order = e4b->bd_blkbits + 1;
	int max;
	int max2;
	int i;
	int j;
	int k;
	int count;
	struct ext4_group_info *grp;
	int fragments = 0;
	int fstart;
	struct list_head *cur;
	void *buddy;
	void *buddy2;

	if (e4b->bd_info->bb_check_counter++ % 10)
		return;

	while (order > 1) {
		buddy = mb_find_buddy(e4b, order, &max);
		MB_CHECK_ASSERT(buddy);
		buddy2 = mb_find_buddy(e4b, order - 1, &max2);
		MB_CHECK_ASSERT(buddy2);
		MB_CHECK_ASSERT(buddy != buddy2);
		MB_CHECK_ASSERT(max * 2 == max2);

		count = 0;
		for (i = 0; i < max; i++) {

			if (mb_test_bit(i, buddy)) {
				/* only single bit in buddy2 may be 0 */
				if (!mb_test_bit(i << 1, buddy2)) {
					MB_CHECK_ASSERT(
						mb_test_bit((i<<1)+1, buddy2));
				}
				continue;
			}

			/* both bits in buddy2 must be 1 */
			MB_CHECK_ASSERT(mb_test_bit(i << 1, buddy2));
			MB_CHECK_ASSERT(mb_test_bit((i << 1) + 1, buddy2));

			for (j = 0; j < (1 << order); j++) {
				k = (i * (1 << order)) + j;
				MB_CHECK_ASSERT(
					!mb_test_bit(k, e4b->bd_bitmap));
			}
			count++;
		}
		MB_CHECK_ASSERT(e4b->bd_info->bb_counters[order] == count);
		order--;
	}

	fstart = -1;
	buddy = mb_find_buddy(e4b, 0, &max);
	for (i = 0; i < max; i++) {
		if (!mb_test_bit(i, buddy)) {
			MB_CHECK_ASSERT(i >= e4b->bd_info->bb_first_free);
			if (fstart == -1) {
				fragments++;
				fstart = i;
			}
			continue;
		}
		fstart = -1;
		/* check used bits only */
		for (j = 0; j < e4b->bd_blkbits + 1; j++) {
			buddy2 = mb_find_buddy(e4b, j, &max2);
			k = i >> j;
			MB_CHECK_ASSERT(k < max2);
			MB_CHECK_ASSERT(mb_test_bit(k, buddy2));
		}
	}
	MB_CHECK_ASSERT(!EXT4_MB_GRP_NEED_INIT(e4b->bd_info));
	MB_CHECK_ASSERT(e4b->bd_info->bb_fragments == fragments);

	grp = ext4_get_group_info(sb, e4b->bd_group);
	if (!grp)
		return;
	list_for_each(cur, &grp->bb_prealloc_list) {
		ext4_group_t groupnr;
		struct ext4_prealloc_space *pa;
		pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
		ext4_get_group_no_and_offset(sb, pa->pa_pstart, &groupnr, &k);
		MB_CHECK_ASSERT(groupnr == e4b->bd_group);
		for (i = 0; i < pa->pa_len; i++)
			MB_CHECK_ASSERT(mb_test_bit(k + i, buddy));
	}
}
#undef MB_CHECK_ASSERT
#define mb_check_buddy(e4b) __mb_check_buddy(e4b,	\
					__FILE__, __func__, __LINE__)
#else
#define mb_check_buddy(e4b)
#endif

/*
 * Divide blocks started from @first with length @len into
 * smaller chunks with power of 2 blocks.
 * Clear the bits in bitmap which the blocks of the chunk(s) covered,
 * then increase bb_counters[] for corresponded chunk size.
 */
static void ext4_mb_mark_free_simple(struct super_block *sb,
				void *buddy, ext4_grpblk_t first, ext4_grpblk_t len,
					struct ext4_group_info *grp)
{
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	ext4_grpblk_t min;
	ext4_grpblk_t max;
	ext4_grpblk_t chunk;
	unsigned int border;

	BUG_ON(len > EXT4_CLUSTERS_PER_GROUP(sb));

	border = 2 << sb->s_blocksize_bits;

	while (len > 0) {
		/* find how many blocks can be covered since this position */
		max = ffs(first | border) - 1;

		/* find how many blocks of power 2 we need to mark */
		min = fls(len) - 1;

		if (max < min)
			min = max;
		chunk = 1 << min;

		/* mark multiblock chunks only */
		grp->bb_counters[min]++;
		if (min > 0)
			mb_clear_bit(first >> min,
				     buddy + sbi->s_mb_offsets[min]);

		len -= chunk;
		first += chunk;
	}
}

static int mb_avg_fragment_size_order(struct super_block *sb, ext4_grpblk_t len)
{
	int order;

	/*
	 * We don't bother with a special lists groups with only 1 block free
	 * extents and for completely empty groups.
	 */
	order = fls(len) - 2;
	if (order < 0)
		return 0;
	if (order == MB_NUM_ORDERS(sb))
		order--;
	if (WARN_ON_ONCE(order > MB_NUM_ORDERS(sb)))
		order = MB_NUM_ORDERS(sb) - 1;
	return order;
}

/* Move group to appropriate avg_fragment_size list */
static void
mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
{
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	int new_order;

	if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_fragments == 0)
		return;

	new_order = mb_avg_fragment_size_order(sb,
					grp->bb_free / grp->bb_fragments);
	if (new_order == grp->bb_avg_fragment_size_order)
		return;

	if (grp->bb_avg_fragment_size_order != -1) {
		write_lock(&sbi->s_mb_avg_fragment_size_locks[
					grp->bb_avg_fragment_size_order]);
		list_del(&grp->bb_avg_fragment_size_node);
		write_unlock(&sbi->s_mb_avg_fragment_size_locks[
					grp->bb_avg_fragment_size_order]);
	}
	grp->bb_avg_fragment_size_order = new_order;
	write_lock(&sbi->s_mb_avg_fragment_size_locks[
					grp->bb_avg_fragment_size_order]);
	list_add_tail(&grp->bb_avg_fragment_size_node,
		&sbi->s_mb_avg_fragment_size[grp->bb_avg_fragment_size_order]);
	write_unlock(&sbi->s_mb_avg_fragment_size_locks[
					grp->bb_avg_fragment_size_order]);
}

/*
 * Choose next group by traversing largest_free_order lists. Updates *new_cr if
 * cr level needs an update.
 */
static void ext4_mb_choose_next_group_p2_aligned(struct ext4_allocation_context *ac,
			enum criteria *new_cr, ext4_group_t *group)
{
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	struct ext4_group_info *iter;
	int i;

	if (ac->ac_status == AC_STATUS_FOUND)
		return;

	if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED))
		atomic_inc(&sbi->s_bal_p2_aligned_bad_suggestions);

	for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
		if (list_empty(&sbi->s_mb_largest_free_orders[i]))
			continue;
		read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
		if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
			read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
			continue;
		}
		list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
				    bb_largest_free_order_node) {
			if (sbi->s_mb_stats)
				atomic64_inc(&sbi->s_bal_cX_groups_considered[CR_POWER2_ALIGNED]);
			if (likely(ext4_mb_good_group(ac, iter->bb_group, CR_POWER2_ALIGNED))) {
				*group = iter->bb_group;
				ac->ac_flags |= EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED;
				read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
				return;
			}
		}
		read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
	}

	/* Increment cr and search again if no group is found */
	*new_cr = CR_GOAL_LEN_FAST;
}

/*
 * Find a suitable group of given order from the average fragments list.
 */
static struct ext4_group_info *
ext4_mb_find_good_group_avg_frag_lists(struct ext4_allocation_context *ac, int order)
{
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	struct list_head *frag_list = &sbi->s_mb_avg_fragment_size[order];
	rwlock_t *frag_list_lock = &sbi->s_mb_avg_fragment_size_locks[order];
	struct ext4_group_info *grp = NULL, *iter;
	enum criteria cr = ac->ac_criteria;

	if (list_empty(frag_list))
		return NULL;
	read_lock(frag_list_lock);
	if (list_empty(frag_list)) {
		read_unlock(frag_list_lock);
		return NULL;
	}
	list_for_each_entry(iter, frag_list, bb_avg_fragment_size_node) {
		if (sbi->s_mb_stats)
			atomic64_inc(&sbi->s_bal_cX_groups_considered[cr]);
		if (likely(ext4_mb_good_group(ac, iter->bb_group, cr))) {
			grp = iter;
			break;
		}
	}
	read_unlock(frag_list_lock);
	return grp;
}

/*
 * Choose next group by traversing average fragment size list of suitable
 * order. Updates *new_cr if cr level needs an update.
 */
static void ext4_mb_choose_next_group_goal_fast(struct ext4_allocation_context *ac,
		enum criteria *new_cr, ext4_group_t *group)
{
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	struct ext4_group_info *grp = NULL;
	int i;

	if (unlikely(ac->ac_flags & EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED)) {
		if (sbi->s_mb_stats)
			atomic_inc(&sbi->s_bal_goal_fast_bad_suggestions);
	}

	for (i = mb_avg_fragment_size_order(ac->ac_sb, ac->ac_g_ex.fe_len);
	     i < MB_NUM_ORDERS(ac->ac_sb); i++) {
		grp = ext4_mb_find_good_group_avg_frag_lists(ac, i);
		if (grp) {
			*group = grp->bb_group;
			ac->ac_flags |= EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED;
			return;
		}
	}

	/*
	 * CR_BEST_AVAIL_LEN works based on the concept that we have
	 * a larger normalized goal len request which can be trimmed to
	 * a smaller goal len such that it can still satisfy original
	 * request len. However, allocation request for non-regular
	 * files never gets normalized.
	 * See function ext4_mb_normalize_request() (EXT4_MB_HINT_DATA).
	 */
	if (ac->ac_flags & EXT4_MB_HINT_DATA)
		*new_cr = CR_BEST_AVAIL_LEN;
	else
		*new_cr = CR_GOAL_LEN_SLOW;
}

/*
 * We couldn't find a group in CR_GOAL_LEN_FAST so try to find the highest free fragment
 * order we have and proactively trim the goal request length to that order to
 * find a suitable group faster.
 *
 * This optimizes allocation speed at the cost of slightly reduced
 * preallocations. However, we make sure that we don't trim the request too
 * much and fall to CR_GOAL_LEN_SLOW in that case.
 */
static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context *ac,
		enum criteria *new_cr, ext4_group_t *group)
{
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	struct ext4_group_info *grp = NULL;
	int i, order, min_order;
	unsigned long num_stripe_clusters = 0;

	if (unlikely(ac->ac_flags & EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED)) {
		if (sbi->s_mb_stats)
			atomic_inc(&sbi->s_bal_best_avail_bad_suggestions);
	}

	/*
	 * mb_avg_fragment_size_order() returns order in a way that makes
	 * retrieving back the length using (1 << order) inaccurate. Hence, use
	 * fls() instead since we need to know the actual length while modifying
	 * goal length.
	 */
	order = fls(ac->ac_g_ex.fe_len) - 1;
	if (WARN_ON_ONCE(order - 1 > MB_NUM_ORDERS(ac->ac_sb)))
		order = MB_NUM_ORDERS(ac->ac_sb);
	min_order = order - sbi->s_mb_best_avail_max_trim_order;
	if (min_order < 0)
		min_order = 0;

	if (sbi->s_stripe > 0) {
		/*
		 * We are assuming that stripe size is always a multiple of
		 * cluster ratio otherwise __ext4_fill_super exists early.
		 */
		num_stripe_clusters = EXT4_NUM_B2C(sbi, sbi->s_stripe);
		if (1 << min_order < num_stripe_clusters)
			/*
			 * We consider 1 order less because later we round
			 * up the goal len to num_stripe_clusters
			 */
			min_order = fls(num_stripe_clusters) - 1;
	}

	if (1 << min_order < ac->ac_o_ex.fe_len)
		min_order = fls(ac->ac_o_ex.fe_len);

	for (i = order; i >= min_order; i--) {
		int frag_order;
		/*
		 * Scale down goal len to make sure we find something
		 * in the free fragments list. Basically, reduce
		 * preallocations.
		 */
		ac->ac_g_ex.fe_len = 1 << i;

		if (num_stripe_clusters > 0) {
			/*
			 * Try to round up the adjusted goal length to
			 * stripe size (in cluster units) multiple for
			 * efficiency.
			 */
			ac->ac_g_ex.fe_len = roundup(ac->ac_g_ex.fe_len,
						     num_stripe_clusters);
		}

		frag_order = mb_avg_fragment_size_order(ac->ac_sb,
							ac->ac_g_ex.fe_len);

		grp = ext4_mb_find_good_group_avg_frag_lists(ac, frag_order);
		if (grp) {
			*group = grp->bb_group;
			ac->ac_flags |= EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED;
			return;
		}
	}

	/* Reset goal length to original goal length before falling into CR_GOAL_LEN_SLOW */
	ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
	*new_cr = CR_GOAL_LEN_SLOW;
}

static inline int should_optimize_scan(struct ext4_allocation_context *ac)
{
	if (unlikely(!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN)))
		return 0;
	if (ac->ac_criteria >= CR_GOAL_LEN_SLOW)
		return 0;
	if (!ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
		return 0;
	return 1;
}

/*
 * Return next linear group for allocation.
 */
static ext4_group_t
next_linear_group(ext4_group_t group, ext4_group_t ngroups)
{
	/*
	 * Artificially restricted ngroups for non-extent
	 * files makes group > ngroups possible on first loop.
	 */
	return group + 1 >= ngroups ? 0 : group + 1;
}

/*
 * ext4_mb_choose_next_group: choose next group for allocation.
 *
 * @ac        Allocation Context
 * @new_cr    This is an output parameter. If the there is no good group
 *            available at current CR level, this field is updated to indicate
 *            the new cr level that should be used.
 * @group     This is an input / output parameter. As an input it indicates the
 *            next group that the allocator intends to use for allocation. As
 *            output, this field indicates the next group that should be used as
 *            determined by the optimization functions.
 * @ngroups   Total number of groups
 */
static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
		enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
{
	*new_cr = ac->ac_criteria;

	if (!should_optimize_scan(ac)) {
		*group = next_linear_group(*group, ngroups);
		return;
	}

	/*
	 * Optimized scanning can return non adjacent groups which can cause
	 * seek overhead for rotational disks. So try few linear groups before
	 * trying optimized scan.
	 */
	if (ac->ac_groups_linear_remaining) {
		*group = next_linear_group(*group, ngroups);
		ac->ac_groups_linear_remaining--;
		return;
	}

	if (*new_cr == CR_POWER2_ALIGNED) {
		ext4_mb_choose_next_group_p2_aligned(ac, new_cr, group);
	} else if (*new_cr == CR_GOAL_LEN_FAST) {
		ext4_mb_choose_next_group_goal_fast(ac, new_cr, group);
	} else if (*new_cr == CR_BEST_AVAIL_LEN) {
		ext4_mb_choose_next_group_best_avail(ac, new_cr, group);
	} else {
		/*
		 * TODO: For CR_GOAL_LEN_SLOW, we can arrange groups in an
		 * rb tree sorted by bb_free. But until that happens, we should
		 * never come here.
		 */
		WARN_ON(1);
	}
}

/*
 * Cache the order of the largest free extent we have available in this block
 * group.
 */
static void
mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
{
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	int i;

	for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--)
		if (grp->bb_counters[i] > 0)
			break;
	/* No need to move between order lists? */
	if (!test_opt2(sb, MB_OPTIMIZE_SCAN) ||
	    i == grp->bb_largest_free_order) {
		grp->bb_largest_free_order = i;
		return;
	}

	if (grp->bb_largest_free_order >= 0) {
		write_lock(&sbi->s_mb_largest_free_orders_locks[
					      grp->bb_largest_free_order]);
		list_del_init(&grp->bb_largest_free_order_node);
		write_unlock(&sbi->s_mb_largest_free_orders_locks[
					      grp->bb_largest_free_order]);
	}
	grp->bb_largest_free_order = i;
	if (grp->bb_largest_free_order >= 0 && grp->bb_free) {
		write_lock(&sbi->s_mb_largest_free_orders_locks[
					      grp->bb_largest_free_order]);
		list_add_tail(&grp->bb_largest_free_order_node,
		      &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
		write_unlock(&sbi->s_mb_largest_free_orders_locks[
					      grp->bb_largest_free_order]);
	}
}

static noinline_for_stack
void ext4_mb_generate_buddy(struct super_block *sb,
			    void *buddy, void *bitmap, ext4_group_t group,
			    struct ext4_group_info *grp)
{
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
	ext4_grpblk_t i = 0;
	ext4_grpblk_t first;
	ext4_grpblk_t len;
	unsigned free = 0;
	unsigned fragments = 0;
	unsigned long long period = get_cycles();

	/* initialize buddy from bitmap which is aggregation
	 * of on-disk bitmap and preallocations */
	i = mb_find_next_zero_bit(bitmap, max, 0);
	grp->bb_first_free = i;
	while (i < max) {
		fragments++;
		first = i;
		i = mb_find_next_bit(bitmap, max, i);
		len = i - first;
		free += len;
		if (len > 1)
			ext4_mb_mark_free_simple(sb, buddy, first, len, grp);
		else
			grp->bb_counters[0]++;
		if (i < max)
			i = mb_find_next_zero_bit(bitmap, max, i);
	}
	grp->bb_fragments = fragments;

	if (free != grp->bb_free) {
		ext4_grp_locked_error(sb, group, 0, 0,
				      "block bitmap and bg descriptor "
				      "inconsistent: %u vs %u free clusters",
				      free, grp->bb_free);
		/*
		 * If we intend to continue, we consider group descriptor
		 * corrupt and update bb_free using bitmap value
		 */
		grp->bb_free = free;
		ext4_mark_group_bitmap_corrupted(sb, group,
					EXT4_GROUP_INFO_BBITMAP_CORRUPT);
	}
	mb_set_largest_free_order(sb, grp);
	mb_update_avg_fragment_size(sb, grp);

	clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));

	period = get_cycles() - period;
	atomic_inc(&sbi->s_mb_buddies_generated);
	atomic64_add(period, &sbi->s_mb_generation_time);
}

static void mb_regenerate_buddy(struct ext4_buddy *e4b)
{
	int count;
	int order = 1;
	void *buddy;

	while ((buddy = mb_find_buddy(e4b, order++, &count)))
		mb_set_bits(buddy, 0, count);

	e4b->bd_info->bb_fragments = 0;
	memset(e4b->bd_info->bb_counters, 0,
		sizeof(*e4b->bd_info->bb_counters) *
		(e4b->bd_sb->s_blocksize_bits + 2));

	ext4_mb_generate_buddy(e4b->bd_sb, e4b->bd_buddy,
		e4b->bd_bitmap, e4b->bd_group, e4b->bd_info);
}

/* The buddy information is attached the buddy cache inode
 * for convenience. The information regarding each group
 * is loaded via ext4_mb_load_buddy. The information involve
 * block bitmap and buddy information. The information are
 * stored in the inode as
 *
 * {                        page                        }
 * [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.
 * So for each group we take up 2 blocks. A page can
 * contain blocks_per_page (PAGE_SIZE / blocksize)  blocks.
 * So it can have information regarding groups_per_page which
 * is blocks_per_page/2
 *
 * Locking note:  This routine takes the block group lock of all groups
 * for this page; do not hold this lock when calling this routine!
 */

static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
{
	ext4_group_t ngroups;
	unsigned int blocksize;
	int blocks_per_page;
	int groups_per_page;
	int err = 0;
	int i;
	ext4_group_t first_group, group;
	int first_block;
	struct super_block *sb;
	struct buffer_head *bhs;
	struct buffer_head **bh = NULL;
	struct inode *inode;
	char *data;
	char *bitmap;
	struct ext4_group_info *grinfo;

	inode = folio->mapping->host;
	sb = inode->i_sb;
	ngroups = ext4_get_groups_count(sb);
	blocksize = i_blocksize(inode);
	blocks_per_page = PAGE_SIZE / blocksize;

	mb_debug(sb, "init folio %lu\n", folio->index);

	groups_per_page = blocks_per_page >> 1;
	if (groups_per_page == 0)
		groups_per_page = 1;

	/* allocate buffer_heads to read bitmaps */
	if (groups_per_page > 1) {
		i = sizeof(struct buffer_head *) * groups_per_page;
		bh = kzalloc(i, gfp);
		if (bh == NULL)
			return -ENOMEM;
	} else
		bh = &bhs;

	first_group = folio->index * blocks_per_page / 2;

	/* read all groups the folio covers into the cache */
	for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
		if (group >= ngroups)
			break;

		grinfo = ext4_get_group_info(sb, group);
		if (!grinfo)
			continue;
		/*
		 * If page is uptodate then we came here after online resize
		 * which added some new uninitialized group info structs, so
		 * we must skip all initialized uptodate buddies on the folio,
		 * which may be currently in use by an allocating task.
		 */
		if (folio_test_uptodate(folio) &&
				!EXT4_MB_GRP_NEED_INIT(grinfo)) {
			bh[i] = NULL;
			continue;
		}
		bh[i] = ext4_read_block_bitmap_nowait(sb, group, false);
		if (IS_ERR(bh[i])) {
			err = PTR_ERR(bh[i]);
			bh[i] = NULL;
			goto out;
		}
		mb_debug(sb, "read bitmap for group %u\n", group);
	}

	/* wait for I/O completion */
	for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
		int err2;

		if (!bh[i])
			continue;
		err2 = ext4_wait_block_bitmap(sb, group, bh[i]);
		if (!err)
			err = err2;
	}

	first_block = folio->index * blocks_per_page;
	for (i = 0; i < blocks_per_page; i++) {
		group = (first_block + i) >> 1;
		if (group >= ngroups)
			break;

		if (!bh[group - first_group])
			/* skip initialized uptodate buddy */
			continue;

		if (!buffer_verified(bh[group - first_group]))
			/* Skip faulty bitmaps */
			continue;
		err = 0;

		/*
		 * data carry information regarding this
		 * particular group in the format specified
		 * above
		 *
		 */
		data = folio_address(folio) + (i * blocksize);
		bitmap = bh[group - first_group]->b_data;

		/*
		 * We place the buddy block and bitmap block
		 * close together
		 */
		grinfo = ext4_get_group_info(sb, group);
		if (!grinfo) {
			err = -EFSCORRUPTED;
		        goto out;
		}
		if ((first_block + i) & 1) {
			/* this is block of buddy */
			BUG_ON(incore == NULL);
			mb_debug(sb, "put buddy for group %u in folio %lu/%x\n",
				group, folio->index, i * blocksize);
			trace_ext4_mb_buddy_bitmap_load(sb, group);
			grinfo->bb_fragments = 0;
			memset(grinfo->bb_counters, 0,
			       sizeof(*grinfo->bb_counters) *
			       (MB_NUM_ORDERS(sb)));
			/*
			 * incore got set to the group block bitmap below
			 */
			ext4_lock_group(sb, group);
			/* init the buddy */
			memset(data, 0xff, blocksize);
			ext4_mb_generate_buddy(sb, data, incore, group, grinfo);
			ext4_unlock_group(sb, group);
			incore = NULL;
		} else {
			/* this is block of bitmap */
			BUG_ON(incore != NULL);
			mb_debug(sb, "put bitmap for group %u in folio %lu/%x\n",
				group, folio->index, i * blocksize);
			trace_ext4_mb_bitmap_load(sb, group);

			/* see comments in ext4_mb_put_pa() */
			ext4_lock_group(sb, group);
			memcpy(data, bitmap, blocksize);

			/* mark all preallocated blks used in in-core bitmap */
			ext4_mb_generate_from_pa(sb, data, group);
			WARN_ON_ONCE(!RB_EMPTY_ROOT(&grinfo->bb_free_root));
			ext4_unlock_group(sb, group);

			/* set incore so that the buddy information can be
			 * generated using this
			 */
			incore = data;
		}
	}
	folio_mark_uptodate(folio);

out:
	if (bh) {
		for (i = 0; i < groups_per_page; i++)
			brelse(bh[i]);
		if (bh != &bhs)
			kfree(bh);
	}
	return err;
}

/*
 * Lock the buddy and bitmap pages. This make sure other parallel init_group
 * on the same buddy page doesn't happen whild holding the buddy page lock.
 * Return locked buddy and bitmap pages on e4b struct. If buddy and bitmap
 * are on the same page e4b->bd_buddy_folio is NULL and return value is 0.
 */
static int ext4_mb_get_buddy_page_lock(struct super_block *sb,
		ext4_group_t group, struct ext4_buddy *e4b, gfp_t gfp)
{
	struct inode *inode = EXT4_SB(sb)->s_buddy_cache;
	int block, pnum, poff;
	int blocks_per_page;
	struct folio *folio;

	e4b->bd_buddy_folio = NULL;
	e4b->bd_bitmap_folio = NULL;

	blocks_per_page = PAGE_SIZE / sb->s_blocksize;
	/*
	 * the buddy cache inode stores the block bitmap
	 * and buddy information in consecutive blocks.
	 * So for each group we need two blocks.
	 */
	block = group * 2;
	pnum = block / blocks_per_page;
	poff = block % blocks_per_page;
	folio = __filemap_get_folio(inode->i_mapping, pnum,
			FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp);
	if (IS_ERR(folio))
		return PTR_ERR(folio);
	BUG_ON(folio->mapping != inode->i_mapping);
	e4b->bd_bitmap_folio = folio;
	e4b->bd_bitmap = folio_address(folio) + (poff * sb->s_blocksize);

	if (blocks_per_page >= 2) {
		/* buddy and bitmap are on the same page */
		return 0;
	}

	/* blocks_per_page == 1, hence we need another page for the buddy */
	folio = __filemap_get_folio(inode->i_mapping, block + 1,
			FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp);
	if (IS_ERR(folio))
		return PTR_ERR(folio);
	BUG_ON(folio->mapping != inode->i_mapping);
	e4b->bd_buddy_folio = folio;
	return 0;
}

static void ext4_mb_put_buddy_page_lock(struct ext4_buddy *e4b)
{
	if (e4b->bd_bitmap_folio) {
		folio_unlock(e4b->bd_bitmap_folio);
		folio_put(e4b->bd_bitmap_folio);
	}
	if (e4b->bd_buddy_folio) {
		folio_unlock(e4b->bd_buddy_folio);
		folio_put(e4b->bd_buddy_folio);
	}
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack
int ext4_mb_init_group(struct super_block *sb, ext4_group_t group, gfp_t gfp)
{

	struct ext4_group_info *this_grp;
	struct ext4_buddy e4b;
	struct folio *folio;
	int ret = 0;

	might_sleep();
	mb_debug(sb, "init group %u\n", group);
	this_grp = ext4_get_group_info(sb, group);
	if (!this_grp)
		return -EFSCORRUPTED;

	/*
	 * This ensures that we don't reinit the buddy cache
	 * page which map to the group from which we are already
	 * allocating. If we are looking at the buddy cache we would
	 * have taken a reference using ext4_mb_load_buddy and that
	 * would have pinned buddy page to page cache.
	 * The call to ext4_mb_get_buddy_page_lock will mark the
	 * page accessed.
	 */
	ret = ext4_mb_get_buddy_page_lock(sb, group, &e4b, gfp);
	if (ret || !EXT4_MB_GRP_NEED_INIT(this_grp)) {
		/*
		 * somebody initialized the group
		 * return without doing anything
		 */
		goto err;
	}

	folio = e4b.bd_bitmap_folio;
	ret = ext4_mb_init_cache(folio, NULL, gfp);
	if (ret)
		goto err;
	if (!folio_test_uptodate(folio)) {
		ret = -EIO;
		goto err;
	}

	if (e4b.bd_buddy_folio == NULL) {
		/*
		 * If both the bitmap and buddy are in
		 * the same page we don't need to force
		 * init the buddy
		 */
		ret = 0;
		goto err;
	}
	/* init buddy cache */
	folio = e4b.bd_buddy_folio;
	ret = ext4_mb_init_cache(folio, e4b.bd_bitmap, gfp);
	if (ret)
		goto err;
	if (!folio_test_uptodate(folio)) {
		ret = -EIO;
		goto err;
	}
err:
	ext4_mb_put_buddy_page_lock(&e4b);
	return ret;
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack int
ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group,
		       struct ext4_buddy *e4b, gfp_t gfp)
{
	int blocks_per_page;
	int block;
	int pnum;
	int poff;
	struct folio *folio;
	int ret;
	struct ext4_group_info *grp;
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	struct inode *inode = sbi->s_buddy_cache;

	might_sleep();
	mb_debug(sb, "load group %u\n", group);

	blocks_per_page = PAGE_SIZE / sb->s_blocksize;
	grp = ext4_get_group_info(sb, group);
	if (!grp)
		return -EFSCORRUPTED;

	e4b->bd_blkbits = sb->s_blocksize_bits;
	e4b->bd_info = grp;
	e4b->bd_sb = sb;
	e4b->bd_group = group;
	e4b->bd_buddy_folio = NULL;
	e4b->bd_bitmap_folio = NULL;

	if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
		/*
		 * we need full data about the group
		 * to make a good selection
		 */
		ret = ext4_mb_init_group(sb, group, gfp);
		if (ret)
			return ret;
	}

	/*
	 * the buddy cache inode stores the block bitmap
	 * and buddy information in consecutive blocks.
	 * So for each group we need two blocks.
	 */
	block = group * 2;
	pnum = block / blocks_per_page;
	poff = block % blocks_per_page;

	/* Avoid locking the folio in the fast path ... */
	folio = __filemap_get_folio(inode->i_mapping, pnum, FGP_ACCESSED, 0);
	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
		if (!IS_ERR(folio))
			/*
			 * drop the folio reference and try
			 * to get the folio with lock. If we
			 * are not uptodate that implies
			 * somebody just created the folio but
			 * is yet to initialize it. So
			 * wait for it to initialize.
			 */
			folio_put(folio);
		folio = __filemap_get_folio(inode->i_mapping, pnum,
				FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp);
		if (!IS_ERR(folio)) {
			if (WARN_RATELIMIT(folio->mapping != inode->i_mapping,
	"ext4: bitmap's mapping != inode->i_mapping\n")) {
				/* should never happen */
				folio_unlock(folio);
				ret = -EINVAL;
				goto err;
			}
			if (!folio_test_uptodate(folio)) {
				ret = ext4_mb_init_cache(folio, NULL, gfp);
				if (ret) {
					folio_unlock(folio);
					goto err;
				}
				mb_cmp_bitmaps(e4b, folio_address(folio) +
					       (poff * sb->s_blocksize));
			}
			folio_unlock(folio);
		}
	}
	if (IS_ERR(folio)) {
		ret = PTR_ERR(folio);
		goto err;
	}
	if (!folio_test_uptodate(folio)) {
		ret = -EIO;
		goto err;
	}

	/* Folios marked accessed already */
	e4b->bd_bitmap_folio = folio;
	e4b->bd_bitmap = folio_address(folio) + (poff * sb->s_blocksize);

	block++;
	pnum = block / blocks_per_page;
	poff = block % blocks_per_page;

	folio = __filemap_get_folio(inode->i_mapping, pnum, FGP_ACCESSED, 0);
	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
		if (!IS_ERR(folio))
			folio_put(folio);
		folio = __filemap_get_folio(inode->i_mapping, pnum,
				FGP_LOCK | FGP_ACCESSED | FGP_CREAT, gfp);
		if (!IS_ERR(folio)) {
			if (WARN_RATELIMIT(folio->mapping != inode->i_mapping,
	"ext4: buddy bitmap's mapping != inode->i_mapping\n")) {
				/* should never happen */
				folio_unlock(folio);
				ret = -EINVAL;
				goto err;
			}
			if (!folio_test_uptodate(folio)) {
				ret = ext4_mb_init_cache(folio, e4b->bd_bitmap,
							 gfp);
				if (ret) {
					folio_unlock(folio);
					goto err;
				}
			}
			folio_unlock(folio);
		}
	}
	if (IS_ERR(folio)) {
		ret = PTR_ERR(folio);
		goto err;
	}
	if (!folio_test_uptodate(folio)) {
		ret = -EIO;
		goto err;
	}

	/* Folios marked accessed already */
	e4b->bd_buddy_folio = folio;
	e4b->bd_buddy = folio_address(folio) + (poff * sb->s_blocksize);

	return 0;

err:
	if (!IS_ERR_OR_NULL(folio))
		folio_put(folio);
	if (e4b->bd_bitmap_folio)
		folio_put(e4b->bd_bitmap_folio);

	e4b->bd_buddy = NULL;
	e4b->bd_bitmap = NULL;
	return ret;
}

static int ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
			      struct ext4_buddy *e4b)
{
	return ext4_mb_load_buddy_gfp(sb, group, e4b, GFP_NOFS);
}

static void ext4_mb_unload_buddy(struct ext4_buddy *e4b)
{
	if (e4b->bd_bitmap_folio)
		folio_put(e4b->bd_bitmap_folio);
	if (e4b->bd_buddy_folio)
		folio_put(e4b->bd_buddy_folio);
}


static int mb_find_order_for_block(struct ext4_buddy *e4b, int block)
{
	int order = 1, max;
	void *bb;

	BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
	BUG_ON(block >= (1 << (e4b->bd_blkbits + 3)));

	while (order <= e4b->bd_blkbits + 1) {
		bb = mb_find_buddy(e4b, order, &max);
		if (!mb_test_bit(block >> order, bb)) {
			/* this block is part of buddy of order 'order' */
			return order;
		}
		order++;
	}
	return 0;
}

static void mb_clear_bits(void *bm, int cur, int len)
{
	__u32 *addr;

	len = cur + len;
	while (cur < len) {
		if ((cur & 31) == 0 && (len - cur) >= 32) {
			/* fast path: clear whole word at once */
			addr = bm + (cur >> 3);
			*addr = 0;
			cur += 32;
			continue;
		}
		mb_clear_bit(cur, bm);
		cur++;
	}
}

/* clear bits in given range
 * will return first found zero bit if any, -1 otherwise
 */
static int mb_test_and_clear_bits(void *bm, int cur, int len)
{
	__u32 *addr;
	int zero_bit = -1;

	len = cur + len;
	while (cur < len) {
		if ((cur & 31) == 0 && (len - cur) >= 32) {
			/* fast path: clear whole word at once */
			addr = bm + (cur >> 3);
			if (*addr != (__u32)(-1) && zero_bit == -1)
				zero_bit = cur + mb_find_next_zero_bit(addr, 32, 0);
			*addr = 0;
			cur += 32;
			continue;
		}
		if (!mb_test_and_clear_bit(cur, bm) && zero_bit == -1)
			zero_bit = cur;
		cur++;
	}

	return zero_bit;
}

void mb_set_bits(void *bm, int cur, int len)
{
	__u32 *addr;

	len = cur + len;
	while (cur < len) {
		if ((cur & 31) == 0 && (len - cur) >= 32) {
			/* fast path: set whole word at once */
			addr = bm + (cur >> 3);
			*addr = 0xffffffff;
			cur += 32;
			continue;
		}
		mb_set_bit(cur, bm);
		cur++;
	}
}

static inline int mb_buddy_adjust_border(int* bit, void* bitmap, int side)
{
	if (mb_test_bit(*bit + side, bitmap)) {
		mb_clear_bit(*bit, bitmap);
		(*bit) -= side;
		return 1;
	}
	else {
		(*bit) += side;
		mb_set_bit(*bit, bitmap);
		return -1;
	}
}

static void mb_buddy_mark_free(struct ext4_buddy *e4b, int first, int last)
{
	int max;
	int order = 1;
	void *buddy = mb_find_buddy(e4b, order, &max);

	while (buddy) {
		void *buddy2;

		/* Bits in range [first; last] are known to be set since
		 * corresponding blocks were allocated. Bits in range
		 * (first; last) will stay set because they form buddies on
		 * upper layer. We just deal with borders if they don't
		 * align with upper layer and then go up.
		 * Releasing entire group is all about clearing
		 * single bit of highest order buddy.
		 */

		/* Example:
		 * ---------------------------------
		 * |   1   |   1   |   1   |   1   |
		 * ---------------------------------
		 * | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
		 * ---------------------------------
		 *   0   1   2   3   4   5   6   7
		 *      \_____________________/
		 *
		 * Neither [1] nor [6] is aligned to above layer.
		 * Left neighbour [0] is free, so mark it busy,
		 * decrease bb_counters and extend range to
		 * [0; 6]
		 * Right neighbour [7] is busy. It can't be coaleasced with [6], so
		 * mark [6] free, increase bb_counters and shrink range to
		 * [0; 5].
		 * Then shift range to [0; 2], go up and do the same.
		 */


		if (first & 1)
			e4b->bd_info->bb_counters[order] += mb_buddy_adjust_border(&first, buddy, -1);
		if (!(last & 1))
			e4b->bd_info->bb_counters[order] += mb_buddy_adjust_border(&last, buddy, 1);
		if (first > last)
			break;
		order++;

		buddy2 = mb_find_buddy(e4b, order, &max);
		if (!buddy2) {
			mb_clear_bits(buddy, first, last - first + 1);
			e4b->bd_info->bb_counters[order - 1] += last - first + 1;
			break;
		}
		first >>= 1;
		last >>= 1;
		buddy = buddy2;
	}
}

static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
			   int first, int count)
{
	int left_is_free = 0;
	int right_is_free = 0;
	int block;
	int last = first + count - 1;
	struct super_block *sb = e4b->bd_sb;

	if (WARN_ON(count == 0))
		return;
	BUG_ON(last >= (sb->s_blocksize << 3));
	assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
	/* Don't bother if the block group is corrupt. */
	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(e4b->bd_info)))
		return;

	mb_check_buddy(e4b);
	mb_free_blocks_double(inode, e4b, first, count);

	/* access memory sequentially: check left neighbour,
	 * clear range and then check right neighbour
	 */
	if (first != 0)
		left_is_free = !mb_test_bit(first - 1, e4b->bd_bitmap);
	block = mb_test_and_clear_bits(e4b->bd_bitmap, first, count);
	if (last + 1 < EXT4_SB(sb)->s_mb_maxs[0])
		right_is_free = !mb_test_bit(last + 1, e4b->bd_bitmap);

	if (unlikely(block != -1)) {
		struct ext4_sb_info *sbi = EXT4_SB(sb);
		ext4_fsblk_t blocknr;

		/*
		 * Fastcommit replay can free already freed blocks which
		 * corrupts allocation info. Regenerate it.
		 */
		if (sbi->s_mount_state & EXT4_FC_REPLAY) {
			mb_regenerate_buddy(e4b);
			goto check;
		}

		blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
		blocknr += EXT4_C2B(sbi, block);
		ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
				EXT4_GROUP_INFO_BBITMAP_CORRUPT);
		ext4_grp_locked_error(sb, e4b->bd_group,
				      inode ? inode->i_ino : 0, blocknr,
				      "freeing already freed block (bit %u); block bitmap corrupt.",
				      block);
		return;
	}

	this_cpu_inc(discard_pa_seq);
	e4b->bd_info->bb_free += count;
	if (first < e4b->bd_info->bb_first_free)
		e4b->bd_info->bb_first_free = first;

	/* let's maintain fragments counter */
	if (left_is_free && right_is_free)
		e4b->bd_info->bb_fragments--;
	else if (!left_is_free && !right_is_free)
		e4b->bd_info->bb_fragments++;

	/* buddy[0] == bd_bitmap is a special case, so handle
	 * it right away and let mb_buddy_mark_free stay free of
	 * zero order checks.
	 * Check if neighbours are to be coaleasced,
	 * adjust bitmap bb_counters and borders appropriately.
	 */
	if (first & 1) {
		first += !left_is_free;
		e4b->bd_info->bb_counters[0] += left_is_free ? -1 : 1;
	}
	if (!(last & 1)) {
		last -= !right_is_free;
		e4b->bd_info->bb_counters[0] += right_is_free ? -1 : 1;
	}

	if (first <= last)
		mb_buddy_mark_free(e4b, first >> 1, last >> 1);

	mb_set_largest_free_order(sb, e4b->bd_info);
	mb_update_avg_fragment_size(sb, e4b->bd_info);
check:
	mb_check_buddy(e4b);
}

static int mb_find_extent(struct ext4_buddy *e4b, int block,
				int needed, struct ext4_free_extent *ex)
{
	int max, order, next;
	void *buddy;

	assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
	BUG_ON(ex == NULL);

	buddy = mb_find_buddy(e4b, 0, &max);
	BUG_ON(buddy == NULL);
	BUG_ON(block >= max);
	if (mb_test_bit(block, buddy)) {
		ex->fe_len = 0;
		ex->fe_start = 0;
		ex->fe_group = 0;
		return 0;
	}

	/* find actual order */
	order = mb_find_order_for_block(e4b, block);

	ex->fe_len = (1 << order) - (block & ((1 << order) - 1));
	ex->fe_start = block;
	ex->fe_group = e4b->bd_group;

	block = block >> order;

	while (needed > ex->fe_len &&
	       mb_find_buddy(e4b, order, &max)) {

		if (block + 1 >= max)
			break;

		next = (block + 1) * (1 << order);
		if (mb_test_bit(next, e4b->bd_bitmap))
			break;

		order = mb_find_order_for_block(e4b, next);

		block = next >> order;
		ex->fe_len += 1 << order;
	}

	if (ex->fe_start + ex->fe_len > EXT4_CLUSTERS_PER_GROUP(e4b->bd_sb)) {
		/* Should never happen! (but apparently sometimes does?!?) */
		WARN_ON(1);
		ext4_grp_locked_error(e4b->bd_sb, e4b->bd_group, 0, 0,
			"corruption or bug in mb_find_extent "
			"block=%d, order=%d needed=%d ex=%u/%d/%d@%u",
			block, order, needed, ex->fe_group, ex->fe_start,
			ex->fe_len, ex->fe_logical);
		ex->fe_len = 0;
		ex->fe_start = 0;
		ex->fe_group = 0;
	}
	return ex->fe_len;
}

static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
{
	int ord;
	int mlen = 0;
	int max = 0;
	int start = ex->fe_start;
	int len = ex->fe_len;
	unsigned ret = 0;
	int len0 = len;
	void *buddy;
	int ord_start, ord_end;

	BUG_ON(start + len > (e4b->bd_sb->s_blocksize << 3));
	BUG_ON(e4b->bd_group != ex->fe_group);
	assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
	mb_check_buddy(e4b);
	mb_mark_used_double(e4b, start, len);

	this_cpu_inc(discard_pa_seq);
	e4b->bd_info->bb_free -= len;
	if (e4b->bd_info->bb_first_free == start)
		e4b->bd_info->bb_first_free += len;

	/* let's maintain fragments counter */
	if (start != 0)
		mlen = !mb_test_bit(start - 1, e4b->bd_bitmap);
	if (start + len < EXT4_SB(e4b->bd_sb)->s_mb_maxs[0])
		max = !mb_test_bit(start + len, e4b->bd_bitmap);
	if (mlen && max)
		e4b->bd_info->bb_fragments++;
	else if (!mlen && !max)
		e4b->bd_info->bb_fragments--;

	/* let's maintain buddy itself */
	while (len) {
		ord = mb_find_order_for_block(e4b, start);

		if (((start >> ord) << ord) == start && len >= (1 << ord)) {
			/* the whole chunk may be allocated at once! */
			mlen = 1 << ord;
			buddy = mb_find_buddy(e4b, ord, &max);
			BUG_ON((start >> ord) >= max);
			mb_set_bit(start >> ord, buddy);
			e4b->bd_info->bb_counters[ord]--;
			start += mlen;
			len -= mlen;
			BUG_ON(len < 0);
			continue;
		}

		/* store for history */
		if (ret == 0)
			ret = len | (ord << 16);

		BUG_ON(ord <= 0);
		buddy = mb_find_buddy(e4b, ord, &max);
		mb_set_bit(start >> ord, buddy);
		e4b->bd_info->bb_counters[ord]--;

		ord_start = (start >> ord) << ord;
		ord_end = ord_start + (1 << ord);
		/* first chunk */
		if (start > ord_start)
			ext4_mb_mark_free_simple(e4b->bd_sb, e4b->bd_buddy,
						 ord_start, start - ord_start,
						 e4b->bd_info);

		/* last chunk */
		if (start + len < ord_end) {
			ext4_mb_mark_free_simple(e4b->bd_sb, e4b->bd_buddy,
						 start + len,
						 ord_end - (start + len),
						 e4b->bd_info);
			break;
		}
		len = start + len - ord_end;
		start = ord_end;
	}
	mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);

	mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
	mb_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
	mb_check_buddy(e4b);

	return ret;
}

/*
 * Must be called under group lock!
 */
static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
					struct ext4_buddy *e4b)
{
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	int ret;

	BUG_ON(ac->ac_b_ex.fe_group != e4b->bd_group);
	BUG_ON(ac->ac_status == AC_STATUS_FOUND);

	ac->ac_b_ex.fe_len = min(ac->ac_b_ex.fe_len, ac->ac_g_ex.fe_len);
	ac->ac_b_ex.fe_logical = ac->ac_g_ex.fe_logical;
	ret = mb_mark_used(e4b, &ac->ac_b_ex);

	/* preallocation can change ac_b_ex, thus we store actually
	 * allocated blocks for history */
	ac->ac_f_ex = ac->ac_b_ex;

	ac->ac_status = AC_STATUS_FOUND;
	ac->ac_tail = ret & 0xffff;
	ac->ac_buddy = ret >> 16;

	/*
	 * take the page reference. We want the page to be pinned
	 * so that we don't get a ext4_mb_init_cache_call for this
	 * group until we update the bitmap. That would mean we
	 * double allocate blocks. The reference is dropped
	 * in ext4_mb_release_context
	 */
	ac->ac_bitmap_folio = e4b->bd_bitmap_folio;
	folio_get(ac->ac_bitmap_folio);
	ac->ac_buddy_folio = e4b->bd_buddy_folio;
	folio_get(ac->ac_buddy_folio);
	/* store last allocated for subsequent stream allocation */
	if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
		spin_lock(&sbi->s_md_lock);
		sbi->s_mb_last_group = ac->ac_f_ex.fe_group;
		sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
		spin_unlock(&sbi->s_md_lock);
	}
	/*
	 * As we've just preallocated more space than
	 * user requested originally, we store allocated
	 * space in a special descriptor.
	 */
	if (ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
		ext4_mb_new_preallocation(ac);

}

static void ext4_mb_check_limits(struct ext4_allocation_context *ac,
					struct ext4_buddy *e4b,
					int finish_group)
{
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	struct ext4_free_extent *bex = &ac->ac_b_ex;
	struct ext4_free_extent *gex = &ac->ac_g_ex;

	if (ac->ac_status == AC_STATUS_FOUND)
		return;
	/*
	 * We don't want to scan for a whole year
	 */
	if (ac->ac_found > sbi->s_mb_max_to_scan &&
			!(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
		ac->ac_status = AC_STATUS_BREAK;
		return;
	}

	/*
	 * Haven't found good chunk so far, let's continue
	 */
	if (bex->fe_len < gex->fe_len)
		return;

	if (finish_group || ac->ac_found > sbi->s_mb_min_to_scan)
		ext4_mb_use_best_found(ac, e4b);
}

/*
 * The routine checks whether found extent is good enough. If it is,
 * then the extent gets marked used and flag is set to the context
 * to stop scanning. Otherwise, the extent is compared with the
 * previous found extent and if new one is better, then it's stored
 * in the context. Later, the best found extent will be used, if
 * mballoc can't find good enough extent.
 *
 * The algorithm used is roughly as follows:
 *
 * * If free extent found is exactly as big as goal, then
 *   stop the scan and use it immediately
 *
 * * If free extent found is smaller than goal, then keep retrying
 *   upto a max of sbi->s_mb_max_to_scan times (default 200). After
 *   that stop scanning and use whatever we have.
 *
 * * If free extent found is bigger than goal, then keep retrying
 *   upto a max of sbi->s_mb_min_to_scan times (default 10) before
 *   stopping the scan and using the extent.
 *
 *
 * FIXME: real allocation policy is to be designed yet!
 */
static void ext4_mb_measure_extent(struct ext4_allocation_context *ac,
					struct ext4_free_extent *ex,
					struct ext4_buddy *e4b)
{
	struct ext4_free_extent *bex = &ac->ac_b_ex;
	struct ext4_free_extent *gex = &ac->ac_g_ex;

	BUG_ON(ex->fe_len <= 0);
	BUG_ON(ex->fe_len > EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));
	BUG_ON(ex->fe_start >= EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));
	BUG_ON(ac->ac_status != AC_STATUS_CONTINUE);

	ac->ac_found++;
	ac->ac_cX_found[ac->ac_criteria]++;

	/*
	 * The special case - take what you catch first
	 */
	if (unlikely(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
		*bex = *ex;
		ext4_mb_use_best_found(ac, e4b);
		return;
	}

	/*
	 * Let's check whether the chuck is good enough
	 */
	if (ex->fe_len == gex->fe_len) {
		*bex = *ex;
		ext4_mb_use_best_found(ac, e4b);
		return;
	}

	/*
	 * If this is first found extent, just store it in the context
	 */
	if (bex->fe_len == 0) {
		*bex = *ex;
		return;
	}

	/*
	 * If new found extent is better, store it in the context
	 */
	if (bex->fe_len < gex->fe_len) {
		/* if the request isn't satisfied, any found extent
		 * larger than previous best one is better */
		if (ex->fe_len > bex->fe_len)
			*bex = *ex;
	} else if (ex->fe_len > gex->fe_len) {
		/* if the request is satisfied, then we try to find
		 * an extent that still satisfy the request, but is
		 * smaller than previous one */
		if (ex->fe_len < bex->fe_len)
			*bex = *ex;
	}

	ext4_mb_check_limits(ac, e4b, 0);
}

static noinline_for_stack
void ext4_mb_try_best_found(struct ext4_allocation_context *ac,
					struct ext4_buddy *e4b)
{
	struct ext4_free_extent ex = ac->ac_b_ex;
	ext4_group_t group = ex.fe_group;
	int max;
	int err;

	BUG_ON(ex.fe_len <= 0);
	err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
	if (err)
		return;

	ext4_lock_group(ac->ac_sb, group);
	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(e4b->bd_info)))
		goto out;

	max = mb_find_extent(e4b, ex.fe_start, ex.fe_len, &ex);

	if (max > 0) {
		ac->ac_b_ex = ex;
		ext4_mb_use_best_found(ac, e4b);
	}

out:
	ext4_unlock_group(ac->ac_sb, group);
	ext4_mb_unload_buddy(e4b);
}

static noinline_for_stack
int ext4_mb_find_by_goal(struct ext4_allocation_context *ac,
				struct ext4_buddy *e4b)
{
	ext4_group_t group = ac->ac_g_ex.fe_group;
	int max;
	int err;
	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
	struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
	struct ext4_free_extent ex;

	if (!grp)
		return -EFSCORRUPTED;
	if (!(ac->ac_flags & (EXT4_MB_HINT_TRY_GOAL | EXT4_MB_HINT_GOAL_ONLY)))
		return 0;
	if (grp->bb_free == 0)
		return 0;

	err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
	if (err)
		return err;

	ext4_lock_group(ac->ac_sb, group);
	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(e4b->bd_info)))
		goto out;

	max = mb_find_extent(e4b, ac->ac_g_ex.fe_start,
			     ac->ac_g_ex.fe_len, &ex);
	ex.fe_logical = 0xDEADFA11; /* debug value */

	if (max >= ac->ac_g_ex.fe_len &&
	    ac->ac_g_ex.fe_len == EXT4_B2C(sbi, sbi->s_stripe)) {
		ext4_fsblk_t start;

		start = ext4_grp_offs_to_block(ac->ac_sb, &ex);
		/* use do_div to get remainder (would be 64-bit modulo) */
		if (do_div(start, sbi->s_stripe) == 0) {
			ac->ac_found++;
			ac->ac_b_ex = ex;
			ext4_mb_use_best_found(ac, e4b);
		}
	} else if (max >= ac->ac_g_ex.fe_len) {
		BUG_ON(ex.fe_len <= 0);
		BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
		BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
		ac->ac_found++;
		ac->ac_b_ex = ex;
		ext4_mb_use_best_found(ac, e4b);
	} else if (max > 0 && (ac->ac_flags & EXT4_MB_HINT_MERGE)) {
		/* Sometimes, caller may want to merge even small
		 * number of blocks to an existing extent */
		BUG_ON(ex.fe_len <= 0);
		BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
		BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
		ac->ac_found++;
		ac->ac_b_ex = ex;
		ext4_mb_use_best_found(ac, e4b);
	}
out:
	ext4_unlock_group(ac->ac_sb, group);
	ext4_mb_unload_buddy(e4b);

	return 0;
}

/*
 * The routine scans buddy structures (not bitmap!) from given order
 * to max order and tries to find big enough chunk to satisfy the req
 */
static noinline_for_stack
void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
					struct ext4_buddy *e4b)
{
	struct super_block *sb = ac->ac_sb;
	struct ext4_group_info *grp = e4b->bd_info;
	void *buddy;
	int i;
	int k;
	int max;

	BUG_ON(ac->ac_2order <= 0);
	for (i = ac->ac_2order; i < MB_NUM_ORDERS(sb); i++) {
		if (grp->bb_counters[i] == 0)
			continue;

		buddy = mb_find_buddy(e4b, i, &max);
		if (WARN_RATELIMIT(buddy == NULL,
			 "ext4: mb_simple_scan_group: mb_find_buddy failed, (%d)\n", i))
			continue;

		k = mb_find_next_zero_bit(buddy, max, 0);
		if (k >= max) {
			ext4_mark_group_bitmap_corrupted(ac->ac_sb,
					e4b->bd_group,
					EXT4_GROUP_INFO_BBITMAP_CORRUPT);
			ext4_grp_locked_error(ac->ac_sb, e4b->bd_group, 0, 0,
				"%d free clusters of order %d. But found 0",
				grp->bb_counters[i], i);
			break;
		}
		ac->ac_found++;
		ac->ac_cX_found[ac->ac_criteria]++;

		ac->ac_b_ex.fe_len = 1 << i;
		ac->ac_b_ex.fe_start = k << i;
		ac->ac_b_ex.fe_group = e4b->bd_group;

		ext4_mb_use_best_found(ac, e4b);

		BUG_ON(ac->ac_f_ex.fe_len != ac->ac_g_ex.fe_len);

		if (EXT4_SB(sb)->s_mb_stats)
			atomic_inc(&EXT4_SB(sb)->s_bal_2orders);

		break;
	}
}

/*
 * The routine scans the group and measures all found extents.
 * In order to optimize scanning, caller must pass number of
 * free blocks in the group, so the routine can know upper limit.
 */
static noinline_for_stack
void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
					struct ext4_buddy *e4b)
{
	struct super_block *sb = ac->ac_sb;
	void *bitmap = e4b->bd_bitmap;
	struct ext4_free_extent ex;
	int i, j, freelen;
	int free;

	free = e4b->bd_info->bb_free;
	if (WARN_ON(free <= 0))
		return;

	i = e4b->bd_info->bb_first_free;

	while (free && ac->ac_status == AC_STATUS_CONTINUE) {
		i = mb_find_next_zero_bit(bitmap,
						EXT4_CLUSTERS_PER_GROUP(sb), i);
		if (i >= EXT4_CLUSTERS_PER_GROUP(sb)) {
			/*
			 * IF we have corrupt bitmap, we won't find any
			 * free blocks even though group info says we
			 * have free blocks
			 */
			ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
					EXT4_GROUP_INFO_BBITMAP_CORRUPT);
			ext4_grp_locked_error(sb, e4b->bd_group, 0, 0,
					"%d free clusters as per "
					"group info. But bitmap says 0",
					free);
			break;
		}

		if (!ext4_mb_cr_expensive(ac->ac_criteria)) {
			/*
			 * In CR_GOAL_LEN_FAST and CR_BEST_AVAIL_LEN, we are
			 * sure that this group will have a large enough
			 * continuous free extent, so skip over the smaller free
			 * extents
			 */
			j = mb_find_next_bit(bitmap,
						EXT4_CLUSTERS_PER_GROUP(sb), i);
			freelen = j - i;

			if (freelen < ac->ac_g_ex.fe_len) {
				i = j;
				free -= freelen;
				continue;
			}
		}

		mb_find_extent(e4b, i, ac->ac_g_ex.fe_len, &ex);
		if (WARN_ON(ex.fe_len <= 0))
			break;
		if (free < ex.fe_len) {
			ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
					EXT4_GROUP_INFO_BBITMAP_CORRUPT);
			ext4_grp_locked_error(sb, e4b->bd_group, 0, 0,
					"%d free clusters as per "
					"group info. But got %d blocks",
					free, ex.fe_len);
			/*
			 * The number of free blocks differs. This mostly
			 * indicate that the bitmap is corrupt. So exit
			 * without claiming the space.
			 */
			break;
		}
		ex.fe_logical = 0xDEADC0DE; /* debug value */
		ext4_mb_measure_extent(ac, &ex, e4b);

		i += ex.fe_len;
		free -= ex.fe_len;
	}

	ext4_mb_check_limits(ac, e4b, 1);
}

/*
 * This is a special case for storages like raid5
 * we try to find stripe-aligned chunks for stripe-size-multiple requests
 */
static noinline_for_stack
void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
				 struct ext4_buddy *e4b)
{
	struct super_block *sb = ac->ac_sb;
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	void *bitmap = e4b->bd_bitmap;
	struct ext4_free_extent ex;
	ext4_fsblk_t first_group_block;
	ext4_fsblk_t a;
	ext4_grpblk_t i, stripe;
	int max;

	BUG_ON(sbi->s_stripe == 0);

	/* find first stripe-aligned block in group */
	first_group_block = ext4_group_first_block_no(sb, e4b->bd_group);

	a = first_group_block + sbi->s_stripe - 1;
	do_div(a, sbi->s_stripe);
	i = (a * sbi->s_stripe) - first_group_block;

	stripe = EXT4_B2C(sbi, sbi->s_stripe);
	i = EXT4_B2C(sbi, i);
	while (i < EXT4_CLUSTERS_PER_GROUP(sb)) {
		if (!mb_test_bit(i, bitmap)) {
			max = mb_find_extent(e4b, i, stripe, &ex);
			if (max >= stripe) {
				ac->ac_found++;
				ac->ac_cX_found[ac->ac_criteria]++;
				ex.fe_logical = 0xDEADF00D; /* debug value */
				ac->ac_b_ex = ex;
				ext4_mb_use_best_found(ac, e4b);
				break;
			}
		}
		i += stripe;
	}
}

/*
 * This is also called BEFORE we load the buddy bitmap.
 * Returns either 1 or 0 indicating that the group is either suitable
 * for the allocation or not.
 */
static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
				ext4_group_t group, enum criteria cr)
{
	ext4_grpblk_t free, fragments;
	int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
	struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);

	BUG_ON(cr < CR_POWER2_ALIGNED || cr >= EXT4_MB_NUM_CRS);

	if (unlikely(!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
		return false;

	free = grp->bb_free;
	if (free == 0)
		return false;

	fragments = grp->bb_fragments;
	if (fragments == 0)
		return false;

	switch (cr) {
	case CR_POWER2_ALIGNED:
		BUG_ON(ac->ac_2order == 0);

		/* Avoid using the first bg of a flexgroup for data files */
		if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
		    (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&
		    ((group % flex_size) == 0))
			return false;

		if (free < ac->ac_g_ex.fe_len)
			return false;

		if (ac->ac_2order >= MB_NUM_ORDERS(ac->ac_sb))
			return true;

		if (grp->bb_largest_free_order < ac->ac_2order)
			return false;

		return true;
	case CR_GOAL_LEN_FAST:
	case CR_BEST_AVAIL_LEN:
		if ((free / fragments) >= ac->ac_g_ex.fe_len)
			return true;
		break;
	case CR_GOAL_LEN_SLOW:
		if (free >= ac->ac_g_ex.fe_len)
			return true;
		break;
	case CR_ANY_FREE:
		return true;
	default:
		BUG();
	}

	return false;
}

/*
 * This could return negative error code if something goes wrong
 * during ext4_mb_init_group(). This should not be called with
 * ext4_lock_group() held.
 *
 * Note: because we are conditionally operating with the group lock in
 * the EXT4_MB_STRICT_CHECK case, we need to fake out sparse in this
 * function using __acquire and __release.  This means we need to be
 * super careful before messing with the error path handling via "goto
 * out"!
 */
static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
				     ext4_group_t group, enum criteria cr)
{
	struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
	struct super_block *sb = ac->ac_sb;
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	bool should_lock = ac->ac_flags & EXT4_MB_STRICT_CHECK;
	ext4_grpblk_t free;
	int ret = 0;

	if (!grp)
		return -EFSCORRUPTED;
	if (sbi->s_mb_stats)
		atomic64_inc(&sbi->s_bal_cX_groups_considered[ac->ac_criteria]);
	if (should_lock) {
		ext4_lock_group(sb, group);
		__release(ext4_group_lock_ptr(sb, group));
	}
	free = grp->bb_free;
	if (free == 0)
		goto out;
	/*
	 * In all criterias except CR_ANY_FREE we try to avoid groups that
	 * can't possibly satisfy the full goal request due to insufficient
	 * free blocks.
	 */
	if (cr < CR_ANY_FREE && free < ac->ac_g_ex.fe_len)
		goto out;
	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
		goto out;
	if (should_lock) {
		__acquire(ext4_group_lock_ptr(sb, group));
		ext4_unlock_group(sb, group);
	}

	/* We only do this if the grp has never been initialized */
	if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
		struct ext4_group_desc *gdp =
			ext4_get_group_desc(sb, group, NULL);
		int ret;

		/*
		 * CR_POWER2_ALIGNED/CR_GOAL_LEN_FAST is a very optimistic
		 * search to find large good chunks almost for free. If buddy
		 * data is not ready, then this optimization makes no sense. But
		 * we never skip the first block group in a flex_bg, since this
		 * gets used for metadata block allocation, and we want to make
		 * sure we locate metadata blocks in the first block group in
		 * the flex_bg if possible.
		 */
		if (!ext4_mb_cr_expensive(cr) &&
		    (!sbi->s_log_groups_per_flex ||
		     ((group & ((1 << sbi->s_log_groups_per_flex) - 1)) != 0)) &&
		    !(ext4_has_group_desc_csum(sb) &&
		      (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))))
			return 0;
		ret = ext4_mb_init_group(sb, group, GFP_NOFS);
		if (ret)
			return ret;
	}

	if (should_lock) {
		ext4_lock_group(sb, group);
		__release(ext4_group_lock_ptr(sb, group));
	}
	ret = ext4_mb_good_group(ac, group, cr);
out:
	if (should_lock) {
		__acquire(ext4_group_lock_ptr(sb, group));
		ext4_unlock_group(sb, group);
	}
	return ret;
}

/*
 * Start prefetching @nr block bitmaps starting at @group.
 * Return the next group which needs to be prefetched.
 */
ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
			      unsigned int nr, int *cnt)
{
	ext4_group_t ngroups = ext4_get_groups_count(sb);
	struct buffer_head *bh;
	struct blk_plug plug;

	blk_start_plug(&plug);
	while (nr-- > 0) {
		struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group,
								  NULL);
		struct ext4_group_info *grp = ext4_get_group_info(sb, group);

		/*
		 * Prefetch block groups with free blocks; but don't
		 * bother if it is marked uninitialized on disk, since
		 * it won't require I/O to read.  Also only try to
		 * prefetch once, so we avoid getblk() call, which can
		 * be expensive.
		 */
		if (gdp && grp && !EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
		    EXT4_MB_GRP_NEED_INIT(grp) &&
		    ext4_free_group_clusters(sb, gdp) > 0 ) {
			bh = ext4_read_block_bitmap_nowait(sb, group, true);
			if (bh && !IS_ERR(bh)) {
				if (!buffer_uptodate(bh) && cnt)
					(*cnt)++;
				brelse(bh);
			}
		}
		if (++group >= ngroups)
			group = 0;
	}
	blk_finish_plug(&plug);
	return group;
}

/*
 * Prefetching reads the block bitmap into the buffer cache; but we
 * need to make sure that the buddy bitmap in the page cache has been
 * initialized.  Note that ext4_mb_init_group() will block if the I/O
 * is not yet completed, or indeed if it was not initiated by
 * ext4_mb_prefetch did not start the I/O.
 *
 * TODO: We should actually kick off the buddy bitmap setup in a work
 * queue when the buffer I/O is completed, so that we don't block
 * waiting for the block allocation bitmap read to finish when
 * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator().
 */
void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
			   unsigned int nr)
{
	struct ext4_group_desc *gdp;
	struct ext4_group_info *grp;

	while (nr-- > 0) {
		if (!group)
			group = ext4_get_groups_count(sb);
		group--;
		gdp = ext4_get_group_desc(sb, group, NULL);
		grp = ext4_get_group_info(sb, group);

		if (grp && gdp && EXT4_MB_GRP_NEED_INIT(grp) &&
		    ext4_free_group_clusters(sb, gdp) > 0) {
			if (ext4_mb_init_group(sb, group, GFP_NOFS))
				break;
		}
	}
}

static noinline_for_stack int
ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
{
	ext4_group_t prefetch_grp = 0, ngroups, group, i;
	enum criteria new_cr, cr = CR_GOAL_LEN_FAST;
	int err = 0, first_err = 0;
	unsigned int nr = 0, prefetch_ios = 0;
	struct ext4_sb_info *sbi;
	struct super_block *sb;
	struct ext4_buddy e4b;
	int lost;

	sb = ac->ac_sb;
	sbi = EXT4_SB(sb);
	ngroups = ext4_get_groups_count(sb);
	/* non-extent files are limited to low blocks/groups */
	if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)))
		ngroups = sbi->s_blockfile_groups;

	BUG_ON(ac->ac_status == AC_STATUS_FOUND);

	/* first, try the goal */
	err = ext4_mb_find_by_goal(ac, &e4b);
	if (err || ac->ac_status == AC_STATUS_FOUND)
		goto out;

	if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
		goto out;

	/*
	 * ac->ac_2order is set only if the fe_len is a power of 2
	 * if ac->ac_2order is set we also set criteria to CR_POWER2_ALIGNED
	 * so that we try exact allocation using buddy.
	 */
	i = fls(ac->ac_g_ex.fe_len);
	ac->ac_2order = 0;
	/*
	 * We search using buddy data only if the order of the request
	 * is greater than equal to the sbi_s_mb_order2_reqs
	 * You can tune it via /sys/fs/ext4/<partition>/mb_order2_req
	 * We also support searching for power-of-two requests only for
	 * requests upto maximum buddy size we have constructed.
	 */
	if (i >= sbi->s_mb_order2_reqs && i <= MB_NUM_ORDERS(sb)) {
		if (is_power_of_2(ac->ac_g_ex.fe_len))
			ac->ac_2order = array_index_nospec(i - 1,
							   MB_NUM_ORDERS(sb));
	}

	/* if stream allocation is enabled, use global goal */
	if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
		/* TBD: may be hot point */
		spin_lock(&sbi->s_md_lock);
		ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
		ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
		spin_unlock(&sbi->s_md_lock);
	}

	/*
	 * Let's just scan groups to find more-less suitable blocks We
	 * start with CR_GOAL_LEN_FAST, unless it is power of 2
	 * aligned, in which case let's do that faster approach first.
	 */
	if (ac->ac_2order)
		cr = CR_POWER2_ALIGNED;
repeat:
	for (; cr < EXT4_MB_NUM_CRS && ac->ac_status == AC_STATUS_CONTINUE; cr++) {
		ac->ac_criteria = cr;
		/*
		 * searching for the right group start
		 * from the goal value specified
		 */
		group = ac->ac_g_ex.fe_group;
		ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;
		prefetch_grp = group;
		nr = 0;

		for (i = 0, new_cr = cr; i < ngroups; i++,
		     ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
			int ret = 0;

			cond_resched();
			if (new_cr != cr) {
				cr = new_cr;
				goto repeat;
			}

			/*
			 * Batch reads of the block allocation bitmaps
			 * to get multiple READs in flight; limit
			 * prefetching at inexpensive CR, otherwise mballoc
			 * can spend a lot of time loading imperfect groups
			 */
			if ((prefetch_grp == group) &&
			    (ext4_mb_cr_expensive(cr) ||
			     prefetch_ios < sbi->s_mb_prefetch_limit)) {
				nr = sbi->s_mb_prefetch;
				if (ext4_has_feature_flex_bg(sb)) {
					nr = 1 << sbi->s_log_groups_per_flex;
					nr -= group & (nr - 1);
					nr = min(nr, sbi->s_mb_prefetch);
				}
				prefetch_grp = ext4_mb_prefetch(sb, group,
							nr, &prefetch_ios);
			}

			/* This now checks without needing the buddy page */
			ret = ext4_mb_good_group_nolock(ac, group, cr);
			if (ret <= 0) {
				if (!first_err)
					first_err = ret;
				continue;
			}

			err = ext4_mb_load_buddy(sb, group, &e4b);
			if (err)
				goto out;

			ext4_lock_group(sb, group);

			/*
			 * We need to check again after locking the
			 * block group
			 */
			ret = ext4_mb_good_group(ac, group, cr);
			if (ret == 0) {
				ext4_unlock_group(sb, group);
				ext4_mb_unload_buddy(&e4b);
				continue;
			}

			ac->ac_groups_scanned++;
			if (cr == CR_POWER2_ALIGNED)
				ext4_mb_simple_scan_group(ac, &e4b);
			else {
				bool is_stripe_aligned = sbi->s_stripe &&
					!(ac->ac_g_ex.fe_len %
					  EXT4_B2C(sbi, sbi->s_stripe));

				if ((cr == CR_GOAL_LEN_FAST ||
				     cr == CR_BEST_AVAIL_LEN) &&
				    is_stripe_aligned)
					ext4_mb_scan_aligned(ac, &e4b);

				if (ac->ac_status == AC_STATUS_CONTINUE)
					ext4_mb_complex_scan_group(ac, &e4b);
			}

			ext4_unlock_group(sb, group);
			ext4_mb_unload_buddy(&e4b);

			if (ac->ac_status != AC_STATUS_CONTINUE)
				break;
		}
		/* Processed all groups and haven't found blocks */
		if (sbi->s_mb_stats && i == ngroups)
			atomic64_inc(&sbi->s_bal_cX_failed[cr]);

		if (i == ngroups && ac->ac_criteria == CR_BEST_AVAIL_LEN)
			/* Reset goal length to original goal length before
			 * falling into CR_GOAL_LEN_SLOW */
			ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
	}

	if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
	    !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
		/*
		 * We've been searching too long. Let's try to allocate
		 * the best chunk we've found so far
		 */
		ext4_mb_try_best_found(ac, &e4b);
		if (ac->ac_status != AC_STATUS_FOUND) {
			/*
			 * Someone more lucky has already allocated it.
			 * The only thing we can do is just take first
			 * found block(s)
			 */
			lost = atomic_inc_return(&sbi->s_mb_lost_chunks);
			mb_debug(sb, "lost chunk, group: %u, start: %d, len: %d, lost: %d\n",
				 ac->ac_b_ex.fe_group, ac->ac_b_ex.fe_start,
				 ac->ac_b_ex.fe_len, lost);

			ac->ac_b_ex.fe_group = 0;
			ac->ac_b_ex.fe_start = 0;
			ac->ac_b_ex.fe_len = 0;
			ac->ac_status = AC_STATUS_CONTINUE;
			ac->ac_flags |= EXT4_MB_HINT_FIRST;
			cr = CR_ANY_FREE;
			goto repeat;
		}
	}

	if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND)
		atomic64_inc(&sbi->s_bal_cX_hits[ac->ac_criteria]);
out:
	if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
		err = first_err;

	mb_debug(sb, "Best len %d, origin len %d, ac_status %u, ac_flags 0x%x, cr %d ret %d\n",
		 ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status,
		 ac->ac_flags, cr, err);

	if (nr)
		ext4_mb_prefetch_fini(sb, prefetch_grp, nr);

	return err;
}

static void *ext4_mb_seq_groups_start(struct seq_file *seq, loff_t *pos)
{
	struct super_block *sb = pde_data(file_inode(seq->file));
	ext4_group_t group;

	if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
		return NULL;
	group = *pos + 1;
	return (void *) ((unsigned long) group);
}

static void *ext4_mb_seq_groups_next(struct seq_file *seq, void *v, loff_t *pos)
{
	struct super_block *sb = pde_data(file_inode(seq->file));
	ext4_group_t group;

	++*pos;
	if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
		return NULL;
	group = *pos + 1;
	return (void *) ((unsigned long) group);
}

static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
{
	struct super_block *sb = pde_data(file_inode(seq->file));
	ext4_group_t group = (ext4_group_t) ((unsigned long) v);
	int i, err;
	char nbuf[16];
	struct ext4_buddy e4b;
	struct ext4_group_info *grinfo;
	unsigned char blocksize_bits = min_t(unsigned char,
					     sb->s_blocksize_bits,
					     EXT4_MAX_BLOCK_LOG_SIZE);
	struct sg {
		struct ext4_group_info info;
		ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
	} sg;

	group--;
	if (group == 0)
		seq_puts(seq, "#group: free  frags first ["
			      " 2^0   2^1   2^2   2^3   2^4   2^5   2^6  "
			      " 2^7   2^8   2^9   2^10  2^11  2^12  2^13  ]\n");

	i = (blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
		sizeof(struct ext4_group_info);

	grinfo = ext4_get_group_info(sb, group);
	if (!grinfo)
		return 0;
	/* Load the group info in memory only if not already loaded. */
	if (unlikely(EXT4_MB_GRP_NEED_INIT(grinfo))) {
		err = ext4_mb_load_buddy(sb, group, &e4b);
		if (err) {
			seq_printf(seq, "#%-5u: %s\n", group, ext4_decode_error(NULL, err, nbuf));
			return 0;
		}
		ext4_mb_unload_buddy(&e4b);
	}

	/*
	 * We care only about free space counters in the group info and
	 * these are safe to access even after the buddy has been unloaded
	 */
	memcpy(&sg, grinfo, i);
	seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
			sg.info.bb_fragments, sg.info.bb_first_free);
	for (i = 0; i <= 13; i++)
		seq_printf(seq, " %-5u", i <= blocksize_bits + 1 ?
				sg.info.bb_counters[i] : 0);
	seq_puts(seq, " ]");
	if (EXT4_MB_GRP_BBITMAP_CORRUPT(&sg.info))
		seq_puts(seq, " Block bitmap corrupted!");
	seq_puts(seq, "\n");

	return 0;
}

static void ext4_mb_seq_groups_stop(struct seq_file *seq, void *v)
{
}

const struct seq_operations ext4_mb_seq_groups_ops = {
	.start  = ext4_mb_seq_groups_start,
	.next   = ext4_mb_seq_groups_next,
	.stop   = ext4_mb_seq_groups_stop,
	.show   = ext4_mb_seq_groups_show,
};

int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
{
	struct super_block *sb = seq->private;
	struct ext4_sb_info *sbi = EXT4_SB(sb);

	seq_puts(seq, "mballoc:\n");
	if (!sbi->s_mb_stats) {
		seq_puts(seq, "\tmb stats collection turned off.\n");
		seq_puts(
			seq,
			"\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
		return 0;
	}
	seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
	seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));

	seq_printf(seq, "\tgroups_scanned: %u\n",
		   atomic_read(&sbi->s_bal_groups_scanned));

	/* CR_POWER2_ALIGNED stats */
	seq_puts(seq, "\tcr_p2_aligned_stats:\n");
	seq_printf(seq, "\t\thits: %llu\n",
		   atomic64_read(&sbi->s_bal_cX_hits[CR_POWER2_ALIGNED]));
	seq_printf(
		seq, "\t\tgroups_considered: %llu\n",
		atomic64_read(
			&sbi->s_bal_cX_groups_considered