fs/nilfs2/page.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Buffer/page management specific to NILFS
  *
  * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
  *
  * Written by Ryusuke Konishi and Seiji Kihara.
  */

 #include <linux/pagemap.h>
 #include <linux/writeback.h>
 #include <linux/swap.h>
 #include <linux/bitops.h>
 #include <linux/page-flags.h>
 #include <linux/list.h>
 #include <linux/highmem.h>
 #include <linux/pagevec.h>
 #include <linux/gfp.h>
 #include "nilfs.h"
 #include "page.h"
 #include "mdt.h"


 #define NILFS_BUFFER_INHERENT_BITS					\
 	(BIT(BH_Uptodate) | BIT(BH_Mapped) | BIT(BH_NILFS_Node) |	\
 	 BIT(BH_NILFS_Volatile) | BIT(BH_NILFS_Checked))

 static struct buffer_head *__nilfs_get_folio_block(struct folio *folio,
 		unsigned long block, pgoff_t index, int blkbits,
 		unsigned long b_state)

 {
 	unsigned long first_block;
 	struct buffer_head *bh = folio_buffers(folio);

 	if (!bh)
 		bh = create_empty_buffers(folio, 1 << blkbits, b_state);

 	first_block = (unsigned long)index << (PAGE_SHIFT - blkbits);
 	bh = get_nth_bh(bh, block - first_block);

 	touch_buffer(bh);
 	wait_on_buffer(bh);
 	return bh;
 }

 struct buffer_head *nilfs_grab_buffer(struct inode *inode,
 				      struct address_space *mapping,
 				      unsigned long blkoff,
 				      unsigned long b_state)
 {
 	int blkbits = inode->i_blkbits;
 	pgoff_t index = blkoff >> (PAGE_SHIFT - blkbits);
 	struct folio *folio;
 	struct buffer_head *bh;

 	folio = filemap_grab_folio(mapping, index);
 	if (IS_ERR(folio))
 		return NULL;

 	bh = __nilfs_get_folio_block(folio, blkoff, index, blkbits, b_state);
 	if (unlikely(!bh)) {
 		folio_unlock(folio);
 		folio_put(folio);
 		return NULL;
 	}
 	return bh;
 }

 /**
  * nilfs_forget_buffer - discard dirty state
  * @bh: buffer head of the buffer to be discarded
  */
 void nilfs_forget_buffer(struct buffer_head *bh)
 {
 	struct folio *folio = bh->b_folio;
 	const unsigned long clear_bits =
 		(BIT(BH_Uptodate) | BIT(BH_Dirty) | BIT(BH_Mapped) |
 		 BIT(BH_Async_Write) | BIT(BH_NILFS_Volatile) |
 		 BIT(BH_NILFS_Checked) | BIT(BH_NILFS_Redirected) |
 		 BIT(BH_Delay));

 	lock_buffer(bh);
 	set_mask_bits(&bh->b_state, clear_bits, 0);
 	if (nilfs_folio_buffers_clean(folio))
 		__nilfs_clear_folio_dirty(folio);

 	bh->b_blocknr = -1;
 	folio_clear_uptodate(folio);
 	folio_clear_mappedtodisk(folio);
 	unlock_buffer(bh);
 	brelse(bh);
 }

 /**
  * nilfs_copy_buffer -- copy buffer data and flags
  * @dbh: destination buffer
  * @sbh: source buffer
  */
 void nilfs_copy_buffer(struct buffer_head *dbh, struct buffer_head *sbh)
 {
 	void *kaddr0, *kaddr1;
 	unsigned long bits;
 	struct page *spage = sbh->b_page, *dpage = dbh->b_page;
 	struct buffer_head *bh;

 	kaddr0 = kmap_local_page(spage);
 	kaddr1 = kmap_local_page(dpage);
 	memcpy(kaddr1 + bh_offset(dbh), kaddr0 + bh_offset(sbh), sbh->b_size);
 	kunmap_local(kaddr1);
 	kunmap_local(kaddr0);

 	dbh->b_state = sbh->b_state & NILFS_BUFFER_INHERENT_BITS;
 	dbh->b_blocknr = sbh->b_blocknr;
 	dbh->b_bdev = sbh->b_bdev;

 	bh = dbh;
 	bits = sbh->b_state & (BIT(BH_Uptodate) | BIT(BH_Mapped));
 	while ((bh = bh->b_this_page) != dbh) {
 		lock_buffer(bh);
 		bits &= bh->b_state;
 		unlock_buffer(bh);
 	}
 	if (bits & BIT(BH_Uptodate))
 		SetPageUptodate(dpage);
 	else
 		ClearPageUptodate(dpage);
 	if (bits & BIT(BH_Mapped))
 		SetPageMappedToDisk(dpage);
 	else
 		ClearPageMappedToDisk(dpage);
 }

 /**
  * nilfs_folio_buffers_clean - Check if a folio has dirty buffers or not.
  * @folio: Folio to be checked.
  *
  * nilfs_folio_buffers_clean() returns false if the folio has dirty buffers.
  * Otherwise, it returns true.
  */
 bool nilfs_folio_buffers_clean(struct folio *folio)
 {
 	struct buffer_head *bh, *head;

 	bh = head = folio_buffers(folio);
 	do {
 		if (buffer_dirty(bh))
 			return false;
 		bh = bh->b_this_page;
 	} while (bh != head);
 	return true;
 }

 void nilfs_folio_bug(struct folio *folio)
 {
 	struct buffer_head *bh, *head;
 	struct address_space *m;
 	unsigned long ino;

 	if (unlikely(!folio)) {
 		printk(KERN_CRIT "NILFS_FOLIO_BUG(NULL)\n");
 		return;
 	}

 	m = folio->mapping;
 	ino = m ? m->host->i_ino : 0;

 	printk(KERN_CRIT "NILFS_FOLIO_BUG(%p): cnt=%d index#=%llu flags=0x%lx "
 	       "mapping=%p ino=%lu\n",
 	       folio, folio_ref_count(folio),
 	       (unsigned long long)folio->index, folio->flags, m, ino);

 	head = folio_buffers(folio);
 	if (head) {
 		int i = 0;

 		bh = head;
 		do {
 			printk(KERN_CRIT
 			       " BH[%d] %p: cnt=%d block#=%llu state=0x%lx\n",
 			       i++, bh, atomic_read(&bh->b_count),
 			       (unsigned long long)bh->b_blocknr, bh->b_state);
 			bh = bh->b_this_page;
 		} while (bh != head);
 	}
 }

 /**
  * nilfs_copy_folio -- copy the folio with buffers
  * @dst: destination folio
  * @src: source folio
  * @copy_dirty: flag whether to copy dirty states on the folio's buffer heads.
  *
  * This function is for both data folios and btnode folios.  The dirty flag
  * should be treated by caller.  The folio must not be under i/o.
  * Both src and dst folio must be locked
  */
 static void nilfs_copy_folio(struct folio *dst, struct folio *src,
 		bool copy_dirty)
 {
 	struct buffer_head *dbh, *dbufs, *sbh;
 	unsigned long mask = NILFS_BUFFER_INHERENT_BITS;

 	BUG_ON(folio_test_writeback(dst));

 	sbh = folio_buffers(src);
 	dbh = folio_buffers(dst);
 	if (!dbh)
 		dbh = create_empty_buffers(dst, sbh->b_size, 0);

 	if (copy_dirty)
 		mask |= BIT(BH_Dirty);

 	dbufs = dbh;
 	do {
 		lock_buffer(sbh);
 		lock_buffer(dbh);
 		dbh->b_state = sbh->b_state & mask;
 		dbh->b_blocknr = sbh->b_blocknr;
 		dbh->b_bdev = sbh->b_bdev;
 		sbh = sbh->b_this_page;
 		dbh = dbh->b_this_page;
 	} while (dbh != dbufs);

 	folio_copy(dst, src);

 	if (folio_test_uptodate(src) && !folio_test_uptodate(dst))
 		folio_mark_uptodate(dst);
 	else if (!folio_test_uptodate(src) && folio_test_uptodate(dst))
 		folio_clear_uptodate(dst);
 	if (folio_test_mappedtodisk(src) && !folio_test_mappedtodisk(dst))
 		folio_set_mappedtodisk(dst);
 	else if (!folio_test_mappedtodisk(src) && folio_test_mappedtodisk(dst))
 		folio_clear_mappedtodisk(dst);

 	do {
 		unlock_buffer(sbh);
 		unlock_buffer(dbh);
 		sbh = sbh->b_this_page;
 		dbh = dbh->b_this_page;
 	} while (dbh != dbufs);
 }

 int nilfs_copy_dirty_pages(struct address_space *dmap,
 			   struct address_space *smap)
 {
 	struct folio_batch fbatch;
 	unsigned int i;
 	pgoff_t index = 0;
 	int err = 0;

 	folio_batch_init(&fbatch);
 repeat:
 	if (!filemap_get_folios_tag(smap, &index, (pgoff_t)-1,
 				PAGECACHE_TAG_DIRTY, &fbatch))
 		return 0;

 	for (i = 0; i < folio_batch_count(&fbatch); i++) {
 		struct folio *folio = fbatch.folios[i], *dfolio;

 		folio_lock(folio);
 		if (unlikely(!folio_test_dirty(folio)))
 			NILFS_FOLIO_BUG(folio, "inconsistent dirty state");

 		dfolio = filemap_grab_folio(dmap, folio->index);
 		if (IS_ERR(dfolio)) {
 			/* No empty page is added to the page cache */
 			folio_unlock(folio);
 			err = PTR_ERR(dfolio);
 			break;
 		}
 		if (unlikely(!folio_buffers(folio)))
 			NILFS_FOLIO_BUG(folio,
 				       "found empty page in dat page cache");

 		nilfs_copy_folio(dfolio, folio, true);
 		filemap_dirty_folio(folio_mapping(dfolio), dfolio);

 		folio_unlock(dfolio);
 		folio_put(dfolio);
 		folio_unlock(folio);
 	}
 	folio_batch_release(&fbatch);
 	cond_resched();

 	if (likely(!err))
 		goto repeat;
 	return err;
 }

 /**
  * nilfs_copy_back_pages -- copy back pages to original cache from shadow cache
  * @dmap: destination page cache
  * @smap: source page cache
  *
  * No pages must be added to the cache during this process.
  * This must be ensured by the caller.
  */
 void nilfs_copy_back_pages(struct address_space *dmap,
 			   struct address_space *smap)
 {
 	struct folio_batch fbatch;
 	unsigned int i, n;
 	pgoff_t start = 0;

 	folio_batch_init(&fbatch);
 repeat:
 	n = filemap_get_folios(smap, &start, ~0UL, &fbatch);
 	if (!n)
 		return;

 	for (i = 0; i < folio_batch_count(&fbatch); i++) {
 		struct folio *folio = fbatch.folios[i], *dfolio;
 		pgoff_t index = folio->index;

 		folio_lock(folio);
 		dfolio = filemap_lock_folio(dmap, index);
 		if (!IS_ERR(dfolio)) {
 			/* overwrite existing folio in the destination cache */
 			WARN_ON(folio_test_dirty(dfolio));
 			nilfs_copy_folio(dfolio, folio, false);
 			folio_unlock(dfolio);
 			folio_put(dfolio);
 			/* Do we not need to remove folio from smap here? */
 		} else {
 			struct folio *f;

 			/* move the folio to the destination cache */
 			xa_lock_irq(&smap->i_pages);
 			f = __xa_erase(&smap->i_pages, index);
 			WARN_ON(folio != f);
 			smap->nrpages--;
 			xa_unlock_irq(&smap->i_pages);

 			xa_lock_irq(&dmap->i_pages);
 			f = __xa_store(&dmap->i_pages, index, folio, GFP_NOFS);
 			if (unlikely(f)) {
 				/* Probably -ENOMEM */
 				folio->mapping = NULL;
 				folio_put(folio);
 			} else {
 				folio->mapping = dmap;
 				dmap->nrpages++;
 				if (folio_test_dirty(folio))
 					__xa_set_mark(&dmap->i_pages, index,
 							PAGECACHE_TAG_DIRTY);
 			}
 			xa_unlock_irq(&dmap->i_pages);
 		}
 		folio_unlock(folio);
 	}
 	folio_batch_release(&fbatch);
 	cond_resched();

 	goto repeat;
 }

 /**
  * nilfs_clear_dirty_pages - discard dirty pages in address space
  * @mapping: address space with dirty pages for discarding
  */
 void nilfs_clear_dirty_pages(struct address_space *mapping)
 {
 	struct folio_batch fbatch;
 	unsigned int i;
 	pgoff_t index = 0;

 	folio_batch_init(&fbatch);

 	while (filemap_get_folios_tag(mapping, &index, (pgoff_t)-1,
 				PAGECACHE_TAG_DIRTY, &fbatch)) {
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			struct folio *folio = fbatch.folios[i];

 			folio_lock(folio);

 			/*
 			 * This folio may have been removed from the address
 			 * space by truncation or invalidation when the lock
 			 * was acquired.  Skip processing in that case.
 			 */
 			if (likely(folio->mapping == mapping))
 				nilfs_clear_folio_dirty(folio);

 			folio_unlock(folio);
 		}
 		folio_batch_release(&fbatch);
 		cond_resched();
 	}
 }

 /**
  * nilfs_clear_folio_dirty - discard dirty folio
  * @folio: dirty folio that will be discarded
  */
 void nilfs_clear_folio_dirty(struct folio *folio)
 {
 	struct buffer_head *bh, *head;

 	BUG_ON(!folio_test_locked(folio));

 	folio_clear_uptodate(folio);
 	folio_clear_mappedtodisk(folio);

 	head = folio_buffers(folio);
 	if (head) {
 		const unsigned long clear_bits =
 			(BIT(BH_Uptodate) | BIT(BH_Dirty) | BIT(BH_Mapped) |
 			 BIT(BH_Async_Write) | BIT(BH_NILFS_Volatile) |
 			 BIT(BH_NILFS_Checked) | BIT(BH_NILFS_Redirected) |
 			 BIT(BH_Delay));

 		bh = head;
 		do {
 			lock_buffer(bh);
 			set_mask_bits(&bh->b_state, clear_bits, 0);
 			unlock_buffer(bh);
 		} while (bh = bh->b_this_page, bh != head);
 	}

 	__nilfs_clear_folio_dirty(folio);
 }

 unsigned int nilfs_page_count_clean_buffers(struct page *page,
 					    unsigned int from, unsigned int to)
 {
 	unsigned int block_start, block_end;
 	struct buffer_head *bh, *head;
 	unsigned int nc = 0;

 	for (bh = head = page_buffers(page), block_start = 0;
 	     bh != head || !block_start;
 	     block_start = block_end, bh = bh->b_this_page) {
 		block_end = block_start + bh->b_size;
 		if (block_end > from && block_start < to && !buffer_dirty(bh))
 			nc++;
 	}
 	return nc;
 }

 /*
  * NILFS2 needs clear_page_dirty() in the following two cases:
  *
  * 1) For B-tree node pages and data pages of DAT file, NILFS2 clears dirty
  *    flag of pages when it copies back pages from shadow cache to the
  *    original cache.
  *
  * 2) Some B-tree operations like insertion or deletion may dispose buffers
  *    in dirty state, and this needs to cancel the dirty state of their pages.
  */
 void __nilfs_clear_folio_dirty(struct folio *folio)
 {
 	struct address_space *mapping = folio->mapping;

 	if (mapping) {
 		xa_lock_irq(&mapping->i_pages);
 		if (folio_test_dirty(folio)) {
 			__xa_clear_mark(&mapping->i_pages, folio->index,
 					     PAGECACHE_TAG_DIRTY);
 			xa_unlock_irq(&mapping->i_pages);
 			folio_clear_dirty_for_io(folio);
 			return;
 		}
 		xa_unlock_irq(&mapping->i_pages);
 		return;
 	}
 	folio_clear_dirty(folio);
 }

 /**
  * nilfs_find_uncommitted_extent - find extent of uncommitted data
  * @inode: inode
  * @start_blk: start block offset (in)
  * @blkoff: start offset of the found extent (out)
  *
  * This function searches an extent of buffers marked "delayed" which
  * starts from a block offset equal to or larger than @start_blk.  If
  * such an extent was found, this will store the start offset in
  * @blkoff and return its length in blocks.  Otherwise, zero is
  * returned.
  */
 unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
 					    sector_t start_blk,
 					    sector_t *blkoff)
 {
 	unsigned int i, nr_folios;
 	pgoff_t index;
 	unsigned long length = 0;
 	struct folio_batch fbatch;
 	struct folio *folio;

 	if (inode->i_mapping->nrpages == 0)
 		return 0;

 	index = start_blk >> (PAGE_SHIFT - inode->i_blkbits);

 	folio_batch_init(&fbatch);

 repeat:
 	nr_folios = filemap_get_folios_contig(inode->i_mapping, &index, ULONG_MAX,
 			&fbatch);
 	if (nr_folios == 0)
 		return length;

 	i = 0;
 	do {
 		folio = fbatch.folios[i];

 		folio_lock(folio);
 		if (folio_buffers(folio)) {
 			struct buffer_head *bh, *head;
 			sector_t b;

 			b = folio->index << (PAGE_SHIFT - inode->i_blkbits);
 			bh = head = folio_buffers(folio);
 			do {
 				if (b < start_blk)
 					continue;
 				if (buffer_delay(bh)) {
 					if (length == 0)
 						*blkoff = b;
 					length++;
 				} else if (length > 0) {
 					goto out_locked;
 				}
 			} while (++b, bh = bh->b_this_page, bh != head);
 		} else {
 			if (length > 0)
 				goto out_locked;
 		}
 		folio_unlock(folio);

 	} while (++i < nr_folios);

 	folio_batch_release(&fbatch);
 	cond_resched();
 	goto repeat;

 out_locked:
 	folio_unlock(folio);
 	folio_batch_release(&fbatch);
 	return length;
 }
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* Buffer/page management specific to NILFS
	*
	* Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
	*
	* Written by Ryusuke Konishi and Seiji Kihara.
	*/

	#include <linux/pagemap.h>
	#include <linux/writeback.h>
	#include <linux/swap.h>
	#include <linux/bitops.h>
	#include <linux/page-flags.h>
	#include <linux/list.h>
	#include <linux/highmem.h>
	#include <linux/pagevec.h>
	#include <linux/gfp.h>
	#include "nilfs.h"
	#include "page.h"
	#include "mdt.h"


	#define NILFS_BUFFER_INHERENT_BITS \
	(BIT(BH_Uptodate) \| BIT(BH_Mapped) \| BIT(BH_NILFS_Node) \| \
	BIT(BH_NILFS_Volatile) \| BIT(BH_NILFS_Checked))

	static struct buffer_head __nilfs_get_folio_block(struct folio folio,
	unsigned long block, pgoff_t index, int blkbits,
	unsigned long b_state)

	{
	unsigned long first_block;
	struct buffer_head *bh = folio_buffers(folio);

	if (!bh)
	bh = create_empty_buffers(folio, 1 << blkbits, b_state);

	first_block = (unsigned long)index << (PAGE_SHIFT - blkbits);
	bh = get_nth_bh(bh, block - first_block);

	touch_buffer(bh);
	wait_on_buffer(bh);
	return bh;
	}

	struct buffer_head nilfs_grab_buffer(struct inode inode,
	struct address_space *mapping,
	unsigned long blkoff,
	unsigned long b_state)
	{
	int blkbits = inode->i_blkbits;
	pgoff_t index = blkoff >> (PAGE_SHIFT - blkbits);
	struct folio *folio;
	struct buffer_head *bh;

	folio = filemap_grab_folio(mapping, index);
	if (IS_ERR(folio))
	return NULL;

	bh = __nilfs_get_folio_block(folio, blkoff, index, blkbits, b_state);
	if (unlikely(!bh)) {
	folio_unlock(folio);
	folio_put(folio);
	return NULL;
	}
	return bh;
	}

	/**
	* nilfs_forget_buffer - discard dirty state
	* @bh: buffer head of the buffer to be discarded
	*/
	void nilfs_forget_buffer(struct buffer_head *bh)
	{
	struct folio *folio = bh->b_folio;
	const unsigned long clear_bits =
	(BIT(BH_Uptodate) \| BIT(BH_Dirty) \| BIT(BH_Mapped) \|
	BIT(BH_Async_Write) \| BIT(BH_NILFS_Volatile) \|
	BIT(BH_NILFS_Checked) \| BIT(BH_NILFS_Redirected) \|
	BIT(BH_Delay));

	lock_buffer(bh);
	set_mask_bits(&bh->b_state, clear_bits, 0);
	if (nilfs_folio_buffers_clean(folio))
	__nilfs_clear_folio_dirty(folio);

	bh->b_blocknr = -1;
	folio_clear_uptodate(folio);
	folio_clear_mappedtodisk(folio);
	unlock_buffer(bh);
	brelse(bh);
	}

	/**
	* nilfs_copy_buffer -- copy buffer data and flags
	* @dbh: destination buffer
	* @sbh: source buffer
	*/
	void nilfs_copy_buffer(struct buffer_head dbh, struct buffer_head sbh)
	{
	void kaddr0, kaddr1;
	unsigned long bits;
	struct page spage = sbh->b_page, dpage = dbh->b_page;
	struct buffer_head *bh;

	kaddr0 = kmap_local_page(spage);
	kaddr1 = kmap_local_page(dpage);
	memcpy(kaddr1 + bh_offset(dbh), kaddr0 + bh_offset(sbh), sbh->b_size);
	kunmap_local(kaddr1);
	kunmap_local(kaddr0);

	dbh->b_state = sbh->b_state & NILFS_BUFFER_INHERENT_BITS;
	dbh->b_blocknr = sbh->b_blocknr;
	dbh->b_bdev = sbh->b_bdev;

	bh = dbh;
	bits = sbh->b_state & (BIT(BH_Uptodate) \| BIT(BH_Mapped));
	while ((bh = bh->b_this_page) != dbh) {
	lock_buffer(bh);
	bits &= bh->b_state;
	unlock_buffer(bh);
	}
	if (bits & BIT(BH_Uptodate))
	SetPageUptodate(dpage);
	else
	ClearPageUptodate(dpage);
	if (bits & BIT(BH_Mapped))
	SetPageMappedToDisk(dpage);
	else
	ClearPageMappedToDisk(dpage);
	}

	/**
	* nilfs_folio_buffers_clean - Check if a folio has dirty buffers or not.
	* @folio: Folio to be checked.
	*
	* nilfs_folio_buffers_clean() returns false if the folio has dirty buffers.
	* Otherwise, it returns true.
	*/
	bool nilfs_folio_buffers_clean(struct folio *folio)
	{
	struct buffer_head bh, head;

	bh = head = folio_buffers(folio);
	do {
	if (buffer_dirty(bh))
	return false;
	bh = bh->b_this_page;
	} while (bh != head);
	return true;
	}

	void nilfs_folio_bug(struct folio *folio)
	{
	struct buffer_head bh, head;
	struct address_space *m;
	unsigned long ino;

	if (unlikely(!folio)) {
	printk(KERN_CRIT "NILFS_FOLIO_BUG(NULL)\n");
	return;
	}

	m = folio->mapping;
	ino = m ? m->host->i_ino : 0;

	printk(KERN_CRIT "NILFS_FOLIO_BUG(%p): cnt=%d index#=%llu flags=0x%lx "
	"mapping=%p ino=%lu\n",
	folio, folio_ref_count(folio),
	(unsigned long long)folio->index, folio->flags, m, ino);

	head = folio_buffers(folio);
	if (head) {
	int i = 0;

	bh = head;
	do {
	printk(KERN_CRIT
	" BH[%d] %p: cnt=%d block#=%llu state=0x%lx\n",
	i++, bh, atomic_read(&bh->b_count),
	(unsigned long long)bh->b_blocknr, bh->b_state);
	bh = bh->b_this_page;
	} while (bh != head);
	}
	}

	/**
	* nilfs_copy_folio -- copy the folio with buffers
	* @dst: destination folio
	* @src: source folio
	* @copy_dirty: flag whether to copy dirty states on the folio's buffer heads.
	*
	* This function is for both data folios and btnode folios. The dirty flag
	* should be treated by caller. The folio must not be under i/o.
	* Both src and dst folio must be locked
	*/
	static void nilfs_copy_folio(struct folio dst, struct folio src,
	bool copy_dirty)
	{
	struct buffer_head dbh, dbufs, *sbh;
	unsigned long mask = NILFS_BUFFER_INHERENT_BITS;

	BUG_ON(folio_test_writeback(dst));

	sbh = folio_buffers(src);
	dbh = folio_buffers(dst);
	if (!dbh)
	dbh = create_empty_buffers(dst, sbh->b_size, 0);

	if (copy_dirty)
	mask \|= BIT(BH_Dirty);

	dbufs = dbh;
	do {
	lock_buffer(sbh);
	lock_buffer(dbh);
	dbh->b_state = sbh->b_state & mask;
	dbh->b_blocknr = sbh->b_blocknr;
	dbh->b_bdev = sbh->b_bdev;
	sbh = sbh->b_this_page;
	dbh = dbh->b_this_page;
	} while (dbh != dbufs);

	folio_copy(dst, src);

	if (folio_test_uptodate(src) && !folio_test_uptodate(dst))
	folio_mark_uptodate(dst);
	else if (!folio_test_uptodate(src) && folio_test_uptodate(dst))
	folio_clear_uptodate(dst);
	if (folio_test_mappedtodisk(src) && !folio_test_mappedtodisk(dst))
	folio_set_mappedtodisk(dst);
	else if (!folio_test_mappedtodisk(src) && folio_test_mappedtodisk(dst))
	folio_clear_mappedtodisk(dst);

	do {
	unlock_buffer(sbh);
	unlock_buffer(dbh);
	sbh = sbh->b_this_page;
	dbh = dbh->b_this_page;
	} while (dbh != dbufs);
	}

	int nilfs_copy_dirty_pages(struct address_space *dmap,
	struct address_space *smap)
	{
	struct folio_batch fbatch;
	unsigned int i;
	pgoff_t index = 0;
	int err = 0;

	folio_batch_init(&fbatch);
	repeat:
	if (!filemap_get_folios_tag(smap, &index, (pgoff_t)-1,
	PAGECACHE_TAG_DIRTY, &fbatch))
	return 0;

	for (i = 0; i < folio_batch_count(&fbatch); i++) {
	struct folio folio = fbatch.folios[i], dfolio;

	folio_lock(folio);
	if (unlikely(!folio_test_dirty(folio)))
	NILFS_FOLIO_BUG(folio, "inconsistent dirty state");

	dfolio = filemap_grab_folio(dmap, folio->index);
	if (IS_ERR(dfolio)) {
	/* No empty page is added to the page cache */
	folio_unlock(folio);
	err = PTR_ERR(dfolio);
	break;
	}
	if (unlikely(!folio_buffers(folio)))
	NILFS_FOLIO_BUG(folio,
	"found empty page in dat page cache");

	nilfs_copy_folio(dfolio, folio, true);
	filemap_dirty_folio(folio_mapping(dfolio), dfolio);

	folio_unlock(dfolio);
	folio_put(dfolio);
	folio_unlock(folio);
	}
	folio_batch_release(&fbatch);
	cond_resched();

	if (likely(!err))
	goto repeat;
	return err;
	}

	/**
	* nilfs_copy_back_pages -- copy back pages to original cache from shadow cache
	* @dmap: destination page cache
	* @smap: source page cache
	*
	* No pages must be added to the cache during this process.
	* This must be ensured by the caller.
	*/
	void nilfs_copy_back_pages(struct address_space *dmap,
	struct address_space *smap)
	{
	struct folio_batch fbatch;
	unsigned int i, n;
	pgoff_t start = 0;

	folio_batch_init(&fbatch);
	repeat:
	n = filemap_get_folios(smap, &start, ~0UL, &fbatch);
	if (!n)
	return;

	for (i = 0; i < folio_batch_count(&fbatch); i++) {
	struct folio folio = fbatch.folios[i], dfolio;
	pgoff_t index = folio->index;

	folio_lock(folio);
	dfolio = filemap_lock_folio(dmap, index);
	if (!IS_ERR(dfolio)) {
	/* overwrite existing folio in the destination cache */
	WARN_ON(folio_test_dirty(dfolio));
	nilfs_copy_folio(dfolio, folio, false);
	folio_unlock(dfolio);
	folio_put(dfolio);
	/* Do we not need to remove folio from smap here? */
	} else {
	struct folio *f;

	/* move the folio to the destination cache */
	xa_lock_irq(&smap->i_pages);
	f = __xa_erase(&smap->i_pages, index);
	WARN_ON(folio != f);
	smap->nrpages--;
	xa_unlock_irq(&smap->i_pages);

	xa_lock_irq(&dmap->i_pages);
	f = __xa_store(&dmap->i_pages, index, folio, GFP_NOFS);
	if (unlikely(f)) {
	/* Probably -ENOMEM */
	folio->mapping = NULL;
	folio_put(folio);
	} else {
	folio->mapping = dmap;
	dmap->nrpages++;
	if (folio_test_dirty(folio))
	__xa_set_mark(&dmap->i_pages, index,
	PAGECACHE_TAG_DIRTY);
	}
	xa_unlock_irq(&dmap->i_pages);
	}
	folio_unlock(folio);
	}
	folio_batch_release(&fbatch);
	cond_resched();

	goto repeat;
	}

	/**
	* nilfs_clear_dirty_pages - discard dirty pages in address space
	* @mapping: address space with dirty pages for discarding
	*/
	void nilfs_clear_dirty_pages(struct address_space *mapping)
	{
	struct folio_batch fbatch;
	unsigned int i;
	pgoff_t index = 0;

	folio_batch_init(&fbatch);

	while (filemap_get_folios_tag(mapping, &index, (pgoff_t)-1,
	PAGECACHE_TAG_DIRTY, &fbatch)) {
	for (i = 0; i < folio_batch_count(&fbatch); i++) {
	struct folio *folio = fbatch.folios[i];

	folio_lock(folio);

	/*
	* This folio may have been removed from the address
	* space by truncation or invalidation when the lock
	* was acquired. Skip processing in that case.
	*/
	if (likely(folio->mapping == mapping))
	nilfs_clear_folio_dirty(folio);

	folio_unlock(folio);
	}
	folio_batch_release(&fbatch);
	cond_resched();
	}
	}

	/**
	* nilfs_clear_folio_dirty - discard dirty folio
	* @folio: dirty folio that will be discarded
	*/
	void nilfs_clear_folio_dirty(struct folio *folio)
	{
	struct buffer_head bh, head;

	BUG_ON(!folio_test_locked(folio));

	folio_clear_uptodate(folio);
	folio_clear_mappedtodisk(folio);

	head = folio_buffers(folio);
	if (head) {
	const unsigned long clear_bits =
	(BIT(BH_Uptodate) \| BIT(BH_Dirty) \| BIT(BH_Mapped) \|
	BIT(BH_Async_Write) \| BIT(BH_NILFS_Volatile) \|
	BIT(BH_NILFS_Checked) \| BIT(BH_NILFS_Redirected) \|
	BIT(BH_Delay));

	bh = head;
	do {
	lock_buffer(bh);
	set_mask_bits(&bh->b_state, clear_bits, 0);
	unlock_buffer(bh);
	} while (bh = bh->b_this_page, bh != head);
	}

	__nilfs_clear_folio_dirty(folio);
	}

	unsigned int nilfs_page_count_clean_buffers(struct page *page,
	unsigned int from, unsigned int to)
	{
	unsigned int block_start, block_end;
	struct buffer_head bh, head;
	unsigned int nc = 0;

	for (bh = head = page_buffers(page), block_start = 0;
	bh != head \|\| !block_start;
	block_start = block_end, bh = bh->b_this_page) {
	block_end = block_start + bh->b_size;
	if (block_end > from && block_start < to && !buffer_dirty(bh))
	nc++;
	}
	return nc;
	}

	/*
	* NILFS2 needs clear_page_dirty() in the following two cases:
	*
	* 1) For B-tree node pages and data pages of DAT file, NILFS2 clears dirty
	* flag of pages when it copies back pages from shadow cache to the
	* original cache.
	*
	* 2) Some B-tree operations like insertion or deletion may dispose buffers
	* in dirty state, and this needs to cancel the dirty state of their pages.
	*/
	void __nilfs_clear_folio_dirty(struct folio *folio)
	{
	struct address_space *mapping = folio->mapping;

	if (mapping) {
	xa_lock_irq(&mapping->i_pages);
	if (folio_test_dirty(folio)) {
	__xa_clear_mark(&mapping->i_pages, folio->index,
	PAGECACHE_TAG_DIRTY);
	xa_unlock_irq(&mapping->i_pages);
	folio_clear_dirty_for_io(folio);
	return;
	}
	xa_unlock_irq(&mapping->i_pages);
	return;
	}
	folio_clear_dirty(folio);
	}

	/**
	* nilfs_find_uncommitted_extent - find extent of uncommitted data
	* @inode: inode
	* @start_blk: start block offset (in)
	* @blkoff: start offset of the found extent (out)
	*
	* This function searches an extent of buffers marked "delayed" which
	* starts from a block offset equal to or larger than @start_blk. If
	* such an extent was found, this will store the start offset in
	* @blkoff and return its length in blocks. Otherwise, zero is
	* returned.
	*/
	unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
	sector_t start_blk,
	sector_t *blkoff)
	{
	unsigned int i, nr_folios;
	pgoff_t index;
	unsigned long length = 0;
	struct folio_batch fbatch;
	struct folio *folio;

	if (inode->i_mapping->nrpages == 0)
	return 0;

	index = start_blk >> (PAGE_SHIFT - inode->i_blkbits);

	folio_batch_init(&fbatch);

	repeat:
	nr_folios = filemap_get_folios_contig(inode->i_mapping, &index, ULONG_MAX,
	&fbatch);
	if (nr_folios == 0)
	return length;

	i = 0;
	do {
	folio = fbatch.folios[i];

	folio_lock(folio);
	if (folio_buffers(folio)) {
	struct buffer_head bh, head;
	sector_t b;

	b = folio->index << (PAGE_SHIFT - inode->i_blkbits);
	bh = head = folio_buffers(folio);
	do {
	if (b < start_blk)
	continue;
	if (buffer_delay(bh)) {
	if (length == 0)
	*blkoff = b;
	length++;
	} else if (length > 0) {
	goto out_locked;
	}
	} while (++b, bh = bh->b_this_page, bh != head);
	} else {
	if (length > 0)
	goto out_locked;
	}
	folio_unlock(folio);

	} while (++i < nr_folios);

	folio_batch_release(&fbatch);
	cond_resched();
	goto repeat;

	out_locked:
	folio_unlock(folio);
	folio_batch_release(&fbatch);
	return length;
	}