/*
 * zsmalloc memory allocator
 *
 * Copyright (C) 2011  Nitin Gupta
 *
 * This code is released using a dual license strategy: BSD/GPL
 * You can choose the license that better fits your requirements.
 *
 * Released under the terms of 3-clause BSD License
 * Released under the terms of GNU General Public License Version 2.0
 */


/*
 * This allocator is designed for use with zcache and zram. Thus, the
 * allocator is supposed to work well under low memory conditions. In
 * particular, it never attempts higher order page allocation which is
 * very likely to fail under memory pressure. On the other hand, if we
 * just use single (0-order) pages, it would suffer from very high
 * fragmentation -- any object of size PAGE_SIZE/2 or larger would occupy
 * an entire page. This was one of the major issues with its predecessor
 * (xvmalloc).
 *
 * To overcome these issues, zsmalloc allocates a bunch of 0-order pages
 * and links them together using various 'struct page' fields. These linked
 * pages act as a single higher-order page i.e. an object can span 0-order
 * page boundaries. The code refers to these linked pages as a single entity
 * called zspage.
 *
 * Following is how we use various fields and flags of underlying
 * struct page(s) to form a zspage.
 *
 * Usage of struct page fields:
 *	page->first_page: points to the first component (0-order) page
 *	page->index (union with page->freelist): offset of the first object
 *		starting in this page. For the first page, this is
 *		always 0, so we use this field (aka freelist) to point
 *		to the first free object in zspage.
 *	page->lru: links together all component pages (except the first page)
 *		of a zspage
 *
 *	For _first_ page only:
 *
 *	page->private (union with page->first_page): refers to the
 *		component page after the first page
 *	page->freelist: points to the first free object in zspage.
 *		Free objects are linked together using in-place
 *		metadata.
 *	page->objects: maximum number of objects we can store in this
 *		zspage (class->zspage_order * PAGE_SIZE / class->size)
 *	page->lru: links together first pages of various zspages.
 *		Basically forming list of zspages in a fullness group.
 *	page->mapping: class index and fullness group of the zspage
 *
 * Usage of struct page flags:
 *	PG_private: identifies the first component page
 *	PG_private2: identifies the last component page
 *
 */

#ifdef CONFIG_ZSMALLOC_DEBUG
#define DEBUG
#endif

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>
#include <linux/cpumask.h>
#include <linux/cpu.h>
#include <linux/vmalloc.h>

#include "zsmalloc.h"
#include "zsmalloc_int.h"

/*
 * A zspage's class index and fullness group
 * are encoded in its (first)page->mapping
 */
#define CLASS_IDX_BITS	28
#define FULLNESS_BITS	4
#define CLASS_IDX_MASK	((1 << CLASS_IDX_BITS) - 1)
#define FULLNESS_MASK	((1 << FULLNESS_BITS) - 1)

/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
static DEFINE_PER_CPU(struct mapping_area, zs_map_area);

static int is_first_page(struct page *page)
{
	return PagePrivate(page);
}

static int is_last_page(struct page *page)
{
	return PagePrivate2(page);
}

static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
				enum fullness_group *fullness)
{
	unsigned long m;
	BUG_ON(!is_first_page(page));

	m = (unsigned long)page->mapping;
	*fullness = m & FULLNESS_MASK;
	*class_idx = (m >> FULLNESS_BITS) & CLASS_IDX_MASK;
}

static void set_zspage_mapping(struct page *page, unsigned int class_idx,
				enum fullness_group fullness)
{
	unsigned long m;
	BUG_ON(!is_first_page(page));

	m = ((class_idx & CLASS_IDX_MASK) << FULLNESS_BITS) |
			(fullness & FULLNESS_MASK);
	page->mapping = (struct address_space *)m;
}

static int get_size_class_index(int size)
{
	int idx = 0;

	if (likely(size > ZS_MIN_ALLOC_SIZE))
		idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
				ZS_SIZE_CLASS_DELTA);

	return idx;
}

static enum fullness_group get_fullness_group(struct page *page)
{
	int inuse, max_objects;
	enum fullness_group fg;
	BUG_ON(!is_first_page(page));

	inuse = page->inuse;
	max_objects = page->objects;

	if (inuse == 0)
		fg = ZS_EMPTY;
	else if (inuse == max_objects)
		fg = ZS_FULL;
	else if (inuse <= max_objects / fullness_threshold_frac)
		fg = ZS_ALMOST_EMPTY;
	else
		fg = ZS_ALMOST_FULL;

	return fg;
}

static void insert_zspage(struct page *page, struct size_class *class,
				enum fullness_group fullness)
{
	struct page **head;

	BUG_ON(!is_first_page(page));

	if (fullness >= _ZS_NR_FULLNESS_GROUPS)
		return;

	head = &class->fullness_list[fullness];
	if (*head)
		list_add_tail(&page->lru, &(*head)->lru);

	*head = page;
}

static void remove_zspage(struct page *page, struct size_class *class,
				enum fullness_group fullness)
{
	struct page **head;

	BUG_ON(!is_first_page(page));

	if (fullness >= _ZS_NR_FULLNESS_GROUPS)
		return;

	head = &class->fullness_list[fullness];
	BUG_ON(!*head);
	if (list_empty(&(*head)->lru))
		*head = NULL;
	else if (*head == page)
		*head = (struct page *)list_entry((*head)->lru.next,
					struct page, lru);

	list_del_init(&page->lru);
}

static enum fullness_group fix_fullness_group(struct zs_pool *pool,
						struct page *page)
{
	int class_idx;
	struct size_class *class;
	enum fullness_group currfg, newfg;

	BUG_ON(!is_first_page(page));

	get_zspage_mapping(page, &class_idx, &currfg);
	newfg = get_fullness_group(page);
	if (newfg == currfg)
		goto out;

	class = &pool->size_class[class_idx];
	remove_zspage(page, class, currfg);
	insert_zspage(page, class, newfg);
	set_zspage_mapping(page, class_idx, newfg);

out:
	return newfg;
}

/*
 * We have to decide on how many pages to link together
 * to form a zspage for each size class. This is important
 * to reduce wastage due to unusable space left at end of
 * each zspage which is given as:
 *	wastage = Zp - Zp % size_class
 * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
 *
 * For example, for size class of 3/8 * PAGE_SIZE, we should
 * link together 3 PAGE_SIZE sized pages to form a zspage
 * since then we can perfectly fit in 8 such objects.
 */
static int get_pages_per_zspage(int class_size)
{
	int i, max_usedpc = 0;
	/* zspage order which gives maximum used size per KB */
	int max_usedpc_order = 1;

	for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
		int zspage_size;
		int waste, usedpc;

		zspage_size = i * PAGE_SIZE;
		waste = zspage_size % class_size;
		usedpc = (zspage_size - waste) * 100 / zspage_size;

		if (usedpc > max_usedpc) {
			max_usedpc = usedpc;
			max_usedpc_order = i;
		}
	}

	return max_usedpc_order;
}

/*
 * A single 'zspage' is composed of many system pages which are
 * linked together using fields in struct page. This function finds
 * the first/head page, given any component page of a zspage.
 */
static struct page *get_first_page(struct page *page)
{
	if (is_first_page(page))
		return page;
	else
		return page->first_page;
}

static struct page *get_next_page(struct page *page)
{
	struct page *next;

	if (is_last_page(page))
		next = NULL;
	else if (is_first_page(page))
		next = (struct page *)page->private;
	else
		next = list_entry(page->lru.next, struct page, lru);

	return next;
}

/* Encode <page, obj_idx> as a single handle value */
static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
{
	unsigned long handle;

	if (!page) {
		BUG_ON(obj_idx);
		return NULL;
	}

	handle = page_to_pfn(page) << OBJ_INDEX_BITS;
	handle |= (obj_idx & OBJ_INDEX_MASK);

	return (void *)handle;
}

/* Decode <page, obj_idx> pair from the given object handle */
static void obj_handle_to_location(unsigned long handle, struct page **page,
				unsigned long *obj_idx)
{
	*page = pfn_to_page(handle >> OBJ_INDEX_BITS);
	*obj_idx = handle & OBJ_INDEX_MASK;
}

static unsigned long obj_idx_to_offset(struct page *page,
				unsigned long obj_idx, int class_size)
{
	unsigned long off = 0;

	if (!is_first_page(page))
		off = page->index;

	return off + obj_idx * class_size;
}

static void reset_page(struct page *page)
{
	clear_bit(PG_private, &page->flags);
	clear_bit(PG_private_2, &page->flags);
	set_page_private(page, 0);
	page->mapping = NULL;
	page->freelist = NULL;
	reset_page_mapcount(page);
}

static void free_zspage(struct page *first_page)
{
	struct page *nextp, *tmp, *head_extra;

	BUG_ON(!is_first_page(first_page));
	BUG_ON(first_page->inuse);

	head_extra = (struct page *)page_private(first_page);

	reset_page(first_page);
	__free_page(first_page);

	/* zspage with only 1 system page */
	if (!head_extra)
		return;

	list_for_each_entry_safe(nextp, tmp, &head_extra->lru, lru) {
		list_del(&nextp->lru);
		reset_page(nextp);
		__free_page(nextp);
	}
	reset_page(head_extra);
	__free_page(head_extra);
}

/* Initialize a newly allocated zspage */
static void init_zspage(struct page *first_page, struct size_class *class)
{
	unsigned long off = 0;
	struct page *page = first_page;

	BUG_ON(!is_first_page(first_page));
	while (page) {
		struct page *next_page;
		struct link_free *link;
		unsigned int i, objs_on_page;

		/*
		 * page->index stores offset of first object starting
		 * in the page. For the first page, this is always 0,
		 * so we use first_page->index (aka ->freelist) to store
		 * head of corresponding zspage's freelist.
		 */
		if (page != first_page)
			page->index = off;

		link = (struct link_free *)kmap_atomic(page) +
						off / sizeof(*link);
		objs_on_page = (PAGE_SIZE - off) / class->size;

		for (i = 1; i <= objs_on_page; i++) {
			off += class->size;
			if (off < PAGE_SIZE) {
				link->next = obj_location_to_handle(page, i);
				link += class->size / sizeof(*link);
			}
		}

		/*
		 * We now come to the last (full or partial) object on this
		 * page, which must point to the first object on the next
		 * page (if present)
		 */
		next_page = get_next_page(page);
		link->next = obj_location_to_handle(next_page, 0);
		kunmap_atomic(link);
		page = next_page;
		off = (off + class->size) % PAGE_SIZE;
	}
}

/*
 * Allocate a zspage for the given size class
 */
static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
{
	int i, error;
	struct page *first_page = NULL, *uninitialized_var(prev_page);

	/*
	 * Allocate individual pages and link them together as:
	 * 1. first page->private = first sub-page
	 * 2. all sub-pages are linked together using page->lru
	 * 3. each sub-page is linked to the first page using page->first_page
	 *
	 * For each size class, First/Head pages are linked together using
	 * page->lru. Also, we set PG_private to identify the first page
	 * (i.e. no other sub-page has this flag set) and PG_private_2 to
	 * identify the last page.
	 */
	error = -ENOMEM;
	for (i = 0; i < class->pages_per_zspage; i++) {
		struct page *page;

		page = alloc_page(flags);
		if (!page)
			goto cleanup;

		INIT_LIST_HEAD(&page->lru);
		if (i == 0) {	/* first page */
			SetPagePrivate(page);
			set_page_private(page, 0);
			first_page = page;
			first_page->inuse = 0;
		}
		if (i == 1)
			first_page->private = (unsigned long)page;
		if (i >= 1)
			page->first_page = first_page;
		if (i >= 2)
			list_add(&page->lru, &prev_page->lru);
		if (i == class->pages_per_zspage - 1)	/* last page */
			SetPagePrivate2(page);
		prev_page = page;
	}

	init_zspage(first_page, class);

	first_page->freelist = obj_location_to_handle(first_page, 0);
	/* Maximum number of objects we can store in this zspage */
	first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;

	error = 0; /* Success */

cleanup:
	if (unlikely(error) && first_page) {
		free_zspage(first_page);
		first_page = NULL;
	}

	return first_page;
}

static struct page *find_get_zspage(struct size_class *class)
{
	int i;
	struct page *page;

	for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
		page = class->fullness_list[i];
		if (page)
			break;
	}

	return page;
}

static void zs_copy_map_object(char *buf, struct page *firstpage,
				int off, int size)
{
	struct page *pages[2];
	int sizes[2];
	void *addr;

	pages[0] = firstpage;
	pages[1] = get_next_page(firstpage);
	BUG_ON(!pages[1]);

	sizes[0] = PAGE_SIZE - off;
	sizes[1] = size - sizes[0];

	/* copy object to per-cpu buffer */
	addr = kmap_atomic(pages[0]);
	memcpy(buf, addr + off, sizes[0]);
	kunmap_atomic(addr);
	addr = kmap_atomic(pages[1]);
	memcpy(buf + sizes[0], addr, sizes[1]);
	kunmap_atomic(addr);
}

static void zs_copy_unmap_object(char *buf, struct page *firstpage,
				int off, int size)
{
	struct page *pages[2];
	int sizes[2];
	void *addr;

	pages[0] = firstpage;
	pages[1] = get_next_page(firstpage);
	BUG_ON(!pages[1]);

	sizes[0] = PAGE_SIZE - off;
	sizes[1] = size - sizes[0];

	/* copy per-cpu buffer to object */
	addr = kmap_atomic(pages[0]);
	memcpy(addr + off, buf, sizes[0]);
	kunmap_atomic(addr);
	addr = kmap_atomic(pages[1]);
	memcpy(addr, buf + sizes[0], sizes[1]);
	kunmap_atomic(addr);
}

static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
				void *pcpu)
{
	int cpu = (long)pcpu;
	struct mapping_area *area;

	switch (action) {
	case CPU_UP_PREPARE:
		area = &per_cpu(zs_map_area, cpu);
		/*
		 * Make sure we don't leak memory if a cpu UP notification
		 * and zs_init() race and both call zs_cpu_up() on the same cpu
		 */
		if (area->vm_buf)
			return 0;
		area->vm_buf = (char *)__get_free_page(GFP_KERNEL);
		if (!area->vm_buf)
			return -ENOMEM;
		return 0;
		break;
	case CPU_DEAD:
	case CPU_UP_CANCELED:
		area = &per_cpu(zs_map_area, cpu);
		if (area->vm_buf)
			free_page((unsigned long)area->vm_buf);
		area->vm_buf = NULL;
		break;
	}

	return NOTIFY_OK;
}

static struct notifier_block zs_cpu_nb = {
	.notifier_call = zs_cpu_notifier
};

static void zs_exit(void)
{
	int cpu;

	for_each_online_cpu(cpu)
		zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
	unregister_cpu_notifier(&zs_cpu_nb);
}

static int zs_init(void)
{
	int cpu, ret;

	register_cpu_notifier(&zs_cpu_nb);
	for_each_online_cpu(cpu) {
		ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
		if (notifier_to_errno(ret))
			goto fail;
	}
	return 0;
fail:
	zs_exit();
	return notifier_to_errno(ret);
}

struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
{
	int i, ovhd_size;
	struct zs_pool *pool;

	if (!name)
		return NULL;

	ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
	pool = kzalloc(ovhd_size, GFP_KERNEL);
	if (!pool)
		return NULL;

	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
		int size;
		struct size_class *class;

		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
		if (size > ZS_MAX_ALLOC_SIZE)
			size = ZS_MAX_ALLOC_SIZE;

		class = &pool->size_class[i];
		class->size = size;
		class->index = i;
		spin_lock_init(&class->lock);
		class->pages_per_zspage = get_pages_per_zspage(size);

	}

	pool->flags = flags;
	pool->name = name;

	return pool;
}
EXPORT_SYMBOL_GPL(zs_create_pool);

void zs_destroy_pool(struct zs_pool *pool)
{
	int i;

	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
		int fg;
		struct size_class *class = &pool->size_class[i];

		for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
			if (class->fullness_list[fg]) {
				pr_info("Freeing non-empty class with size "
					"%db, fullness group %d\n",
					class->size, fg);
			}
		}
	}
	kfree(pool);
}
EXPORT_SYMBOL_GPL(zs_destroy_pool);

/**
 * zs_malloc - Allocate block of given size from pool.
 * @pool: pool to allocate from
 * @size: size of block to allocate
 *
 * On success, handle to the allocated object is returned,
 * otherwise 0.
 * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
 */
unsigned long zs_malloc(struct zs_pool *pool, size_t size)
{
	unsigned long obj;
	struct link_free *link;
	int class_idx;
	struct size_class *class;

	struct page *first_page, *m_page;
	unsigned long m_objidx, m_offset;

	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
		return 0;

	class_idx = get_size_class_index(size);
	class = &pool->size_class[class_idx];
	BUG_ON(class_idx != class->index);

	spin_lock(&class->lock);
	first_page = find_get_zspage(class);

	if (!first_page) {
		spin_unlock(&class->lock);
		first_page = alloc_zspage(class, pool->flags);
		if (unlikely(!first_page))
			return 0;

		set_zspage_mapping(first_page, class->index, ZS_EMPTY);
		spin_lock(&class->lock);
		class->pages_allocated += class->pages_per_zspage;
	}

	obj = (unsigned long)first_page->freelist;
	obj_handle_to_location(obj, &m_page, &m_objidx);
	m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);

	link = (struct link_free *)kmap_atomic(m_page) +
					m_offset / sizeof(*link);
	first_page->freelist = link->next;
	memset(link, POISON_INUSE, sizeof(*link));
	kunmap_atomic(link);

	first_page->inuse++;
	/* Now move the zspage to another fullness group, if required */
	fix_fullness_group(pool, first_page);
	spin_unlock(&class->lock);

	return obj;
}
EXPORT_SYMBOL_GPL(zs_malloc);

void zs_free(struct zs_pool *pool, unsigned long obj)
{
	struct link_free *link;
	struct page *first_page, *f_page;
	unsigned long f_objidx, f_offset;

	int class_idx;
	struct size_class *class;
	enum fullness_group fullness;

	if (unlikely(!obj))
		return;

	obj_handle_to_location(obj, &f_page, &f_objidx);
	first_page = get_first_page(f_page);

	get_zspage_mapping(first_page, &class_idx, &fullness);
	class = &pool->size_class[class_idx];
	f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);

	spin_lock(&class->lock);

	/* Insert this object in containing zspage's freelist */
	link = (struct link_free *)((unsigned char *)kmap_atomic(f_page)
							+ f_offset);
	link->next = first_page->freelist;
	kunmap_atomic(link);
	first_page->freelist = (void *)obj;

	first_page->inuse--;
	fullness = fix_fullness_group(pool, first_page);

	if (fullness == ZS_EMPTY)
		class->pages_allocated -= class->pages_per_zspage;

	spin_unlock(&class->lock);

	if (fullness == ZS_EMPTY)
		free_zspage(first_page);
}
EXPORT_SYMBOL_GPL(zs_free);

/**
 * zs_map_object - get address of allocated object from handle.
 * @pool: pool from which the object was allocated
 * @handle: handle returned from zs_malloc
 *
 * Before using an object allocated from zs_malloc, it must be mapped using
 * this function. When done with the object, it must be unmapped using
 * zs_unmap_object.
 *
 * Only one object can be mapped per cpu at a time. There is no protection
 * against nested mappings.
 *
 * This function returns with preemption and page faults disabled.
*/
void *zs_map_object(struct zs_pool *pool, unsigned long handle,
			enum zs_mapmode mm)
{
	struct page *page;
	unsigned long obj_idx, off;

	unsigned int class_idx;
	enum fullness_group fg;
	struct size_class *class;
	struct mapping_area *area;

	BUG_ON(!handle);

	obj_handle_to_location(handle, &page, &obj_idx);
	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
	class = &pool->size_class[class_idx];
	off = obj_idx_to_offset(page, obj_idx, class->size);

	area = &get_cpu_var(zs_map_area);
	if (off + class->size <= PAGE_SIZE) {
		/* this object is contained entirely within a page */
		area->vm_addr = kmap_atomic(page);
		return area->vm_addr + off;
	}

	/* disable page faults to match kmap_atomic() return conditions */
	pagefault_disable();

	if (mm != ZS_MM_WO)
		zs_copy_map_object(area->vm_buf, page, off, class->size);
	area->vm_addr = NULL;
	return area->vm_buf;
}
EXPORT_SYMBOL_GPL(zs_map_object);

void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
{
	struct page *page;
	unsigned long obj_idx, off;

	unsigned int class_idx;
	enum fullness_group fg;
	struct size_class *class;
	struct mapping_area *area;

	area = &__get_cpu_var(zs_map_area);
	/* single-page object fastpath */
	if (area->vm_addr) {
		kunmap_atomic(area->vm_addr);
		goto out;
	}

	/* no write fastpath */
	if (area->vm_mm == ZS_MM_RO)
		goto pfenable;

	BUG_ON(!handle);

	obj_handle_to_location(handle, &page, &obj_idx);
	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
	class = &pool->size_class[class_idx];
	off = obj_idx_to_offset(page, obj_idx, class->size);

	zs_copy_unmap_object(area->vm_buf, page, off, class->size);

pfenable:
	/* enable page faults to match kunmap_atomic() return conditions */
	pagefault_enable();
out:
	put_cpu_var(zs_map_area);
}
EXPORT_SYMBOL_GPL(zs_unmap_object);

u64 zs_get_total_size_bytes(struct zs_pool *pool)
{
	int i;
	u64 npages = 0;

	for (i = 0; i < ZS_SIZE_CLASSES; i++)
		npages += pool->size_class[i].pages_allocated;

	return npages << PAGE_SHIFT;
}
EXPORT_SYMBOL_GPL(zs_get_total_size_bytes);

module_init(zs_init);
module_exit(zs_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");