[PATCH 0/6] mm, swap: clean up swap cache mapping helper

[PATCH 0/6] mm, swap: clean up swap cache mapping helper

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

This series removes usage of folio_index usage in fs/, and remove swap
cache checking in folio_contains.

Currently, the swap cache is already no longer directly exposed to fs,
and swap cache will be more different from page cache. Clean up the
helpers first to simplify the code and eliminate the helpers used for
resolving circular header dependency issue between filemap and swap
headers.

Kairui Song (6):
  fuse: drop usage of folio_index
  btrfs: drop usage of folio_index
  f2fs: drop usage of folio_index
  filemap: do not use folio_contains for swap cache folios
  mm: move folio_index to mm/swap.h and remove no longer needed helper
  mm, swap: remove no longer used swap mapping helper

 fs/btrfs/extent_io.c    |  2 +-
 fs/f2fs/data.c          |  4 ++--
 fs/f2fs/inline.c        |  4 ++--
 fs/f2fs/super.c         |  2 +-
 fs/fuse/file.c          |  4 ++--
 include/linux/pagemap.h | 29 ++++-------------------------
 mm/memfd.c              |  1 +
 mm/migrate.c            |  1 +
 mm/swap.h               | 18 ++++++++++++++++++
 mm/swapfile.c           | 15 ---------------
 10 files changed, 32 insertions(+), 48 deletions(-)

-- 
2.49.0

[PATCH 1/6] fuse: drop usage of folio_index

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

folio_index is only needed for mixed usage of page cache and swap
cache, for pure page cache usage, the caller can just use
folio->index instead.

It can't be a swap cache folio here.  Swap mapping may only call into fs
through `swap_rw` and that is not supported for fuse.  So just drop it
and use folio->index instead.

uigned-off-by: Kairui Song <kasong@tencent.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kairui Song <kasong@tencent.com>
---
 fs/fuse/file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 754378dd9f71..6f19a4daa559 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -487,7 +487,7 @@ static inline bool fuse_folio_is_writeback(struct inode *inode,
 					   struct folio *folio)
 {
 	pgoff_t last = folio_next_index(folio) - 1;
-	return fuse_range_is_writeback(inode, folio_index(folio), last);
+	return fuse_range_is_writeback(inode, folio->index, last);
 }
 
 static void fuse_wait_on_folio_writeback(struct inode *inode,
@@ -2349,7 +2349,7 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio,
 		return true;
 
 	/* Discontinuity */
-	if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio))
+	if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio->index)
 		return true;
 
 	/* Need to grow the pages array?  If so, did the expansion fail? */
-- 
2.49.0

Re: [PATCH 1/6] fuse: drop usage of folio_index

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:03AM +0800, Kairui Song wrote:
> folio_index is only needed for mixed usage of page cache and swap
> cache, for pure page cache usage, the caller can just use
> folio->index instead.
> 
> It can't be a swap cache folio here.  Swap mapping may only call into fs
> through `swap_rw` and that is not supported for fuse.  So just drop it
> and use folio->index instead.
> 
> uigned-off-by: Kairui Song <kasong@tencent.com>
> Cc: Miklos Szeredi <miklos@szeredi.hu>
> Cc: Joanne Koong <joannelkoong@gmail.com>
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: linux-fsdevel@vger.kernel.org
> Signed-off-by: Kairui Song <kasong@tencent.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

> @@ -2349,7 +2349,7 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio,
>  		return true;
>  
>  	/* Discontinuity */
> -	if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio))
> +	if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio->index)
>  		return true;

This looks like a pre-existing bug.

-	if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio))
+	prev_folio = data->orig_folios[ap->num_folios - 1];
+	if (prev_folio->index + folio_nr_pages(prev_folio) != folio->index)
		return true;

Re: [PATCH 1/6] fuse: drop usage of folio_index

[Kairui Song]

On Mon, Apr 28, 2025 at 8:38 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Apr 28, 2025 at 02:59:03AM +0800, Kairui Song wrote:
> > folio_index is only needed for mixed usage of page cache and swap
> > cache, for pure page cache usage, the caller can just use
> > folio->index instead.
> >
> > It can't be a swap cache folio here.  Swap mapping may only call into fs
> > through `swap_rw` and that is not supported for fuse.  So just drop it
> > and use folio->index instead.
> >
> > uigned-off-by: Kairui Song <kasong@tencent.com>
> > Cc: Miklos Szeredi <miklos@szeredi.hu>
> > Cc: Joanne Koong <joannelkoong@gmail.com>
> > Cc: Josef Bacik <josef@toxicpanda.com>
> > Cc: linux-fsdevel@vger.kernel.org
> > Signed-off-by: Kairui Song <kasong@tencent.com>
>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Thanks for the review.

>
> > @@ -2349,7 +2349,7 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio,
> >               return true;
> >
> >       /* Discontinuity */
> > -     if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio))
> > +     if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio->index)
> >               return true;
>
> This looks like a pre-existing bug.
>
> -       if (data->orig_folios[ap->num_folios - 1]->index + 1 != folio_index(folio))
> +       prev_folio = data->orig_folios[ap->num_folios - 1];
> +       if (prev_folio->index + folio_nr_pages(prev_folio) != folio->index)
>                 return true;
>

It seems FUSE does not work with high order folios yet, a lot of
allocation and operation here are assuming folio size == PAGE_SIZE. I
think I'll just leave it here.

[PATCH 2/6] btrfs: drop usage of folio_index

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

folio_index is only needed for mixed usage of page cache and swap
cache, for pure page cache usage, the caller can just use
folio->index instead.

It can't be a swap cache folio here.  Swap mapping may only call into fs
through `swap_rw` and that is not supported for btrfs.  So just drop it
and use folio->index instead.

Signed-off-by: Kairui Song <kasong@tencent.com>
Cc: Chris Mason <clm@fb.com> (maintainer:BTRFS FILE SYSTEM)
Cc: Josef Bacik <josef@toxicpanda.com> (maintainer:BTRFS FILE SYSTEM)
Cc: David Sterba <dsterba@suse.com> (maintainer:BTRFS FILE SYSTEM)
Cc: linux-btrfs@vger.kernel.org (open list:BTRFS FILE SYSTEM)
Signed-off-by: Kairui Song <kasong@tencent.com>
---
 fs/btrfs/extent_io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 197f5e51c474..e08b50504d13 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3509,7 +3509,7 @@ static void btree_clear_folio_dirty_tag(struct folio *folio)
 	xa_lock_irq(&folio->mapping->i_pages);
 	if (!folio_test_dirty(folio))
 		__xa_clear_mark(&folio->mapping->i_pages,
-				folio_index(folio), PAGECACHE_TAG_DIRTY);
+				folio->index, PAGECACHE_TAG_DIRTY);
 	xa_unlock_irq(&folio->mapping->i_pages);
 }
 
-- 
2.49.0

Re: [PATCH 2/6] btrfs: drop usage of folio_index

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:04AM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> folio_index is only needed for mixed usage of page cache and swap
> cache, for pure page cache usage, the caller can just use
> folio->index instead.
> 
> It can't be a swap cache folio here.  Swap mapping may only call into fs
> through `swap_rw` and that is not supported for btrfs.  So just drop it
> and use folio->index instead.
> 
> Signed-off-by: Kairui Song <kasong@tencent.com>
> Cc: Chris Mason <clm@fb.com> (maintainer:BTRFS FILE SYSTEM)
> Cc: Josef Bacik <josef@toxicpanda.com> (maintainer:BTRFS FILE SYSTEM)
> Cc: David Sterba <dsterba@suse.com> (maintainer:BTRFS FILE SYSTEM)
> Cc: linux-btrfs@vger.kernel.org (open list:BTRFS FILE SYSTEM)
> Signed-off-by: Kairui Song <kasong@tencent.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Re: [PATCH 2/6] btrfs: drop usage of folio_index

[Qu Wenruo]

在 2025/4/28 04:29, Kairui Song 写道:
> From: Kairui Song <kasong@tencent.com>
> 
> folio_index is only needed for mixed usage of page cache and swap
> cache, for pure page cache usage, the caller can just use
> folio->index instead.

The patch looks good to me, but I'm afraid the next commit message is 
not accurate.

> 
> It can't be a swap cache folio here.  Swap mapping may only call into fs
> through `swap_rw` and that is not supported for btrfs.  So just drop it
> and use folio->index instead.

Btrfs supports swap file, it's just not through the swap_rw() callback.

In this particular case, the folio belongs to the metadata (btree) 
inode, thus it will never be swap cache folio.

With that changed, it looks good to me.

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu

> 
> Signed-off-by: Kairui Song <kasong@tencent.com>
> Cc: Chris Mason <clm@fb.com> (maintainer:BTRFS FILE SYSTEM)
> Cc: Josef Bacik <josef@toxicpanda.com> (maintainer:BTRFS FILE SYSTEM)
> Cc: David Sterba <dsterba@suse.com> (maintainer:BTRFS FILE SYSTEM)
> Cc: linux-btrfs@vger.kernel.org (open list:BTRFS FILE SYSTEM)
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
>   fs/btrfs/extent_io.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 197f5e51c474..e08b50504d13 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -3509,7 +3509,7 @@ static void btree_clear_folio_dirty_tag(struct folio *folio)
>   	xa_lock_irq(&folio->mapping->i_pages);
>   	if (!folio_test_dirty(folio))
>   		__xa_clear_mark(&folio->mapping->i_pages,
> -				folio_index(folio), PAGECACHE_TAG_DIRTY);
> +				folio->index, PAGECACHE_TAG_DIRTY);
>   	xa_unlock_irq(&folio->mapping->i_pages);
>   }
>   

Re: [PATCH 2/6] btrfs: drop usage of folio_index

[Kairui Song]

On Mon, Apr 28, 2025 at 8:55 AM Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>
>
>
> 在 2025/4/28 04:29, Kairui Song 写道:
> > From: Kairui Song <kasong@tencent.com>
> >
> > folio_index is only needed for mixed usage of page cache and swap
> > cache, for pure page cache usage, the caller can just use
> > folio->index instead.
>
> The patch looks good to me, but I'm afraid the next commit message is
> not accurate.
>
> >
> > It can't be a swap cache folio here.  Swap mapping may only call into fs
> > through `swap_rw` and that is not supported for btrfs.  So just drop it
> > and use folio->index instead.
>

Thanks for the review.

> Btrfs supports swap file, it's just not through the swap_rw() callback.

Right, I just meant btrfs is not using `swap_rw`. Of course it
supports swap files. Let me update the commit message a bit to clarify
that.

>
> In this particular case, the folio belongs to the metadata (btree)
> inode, thus it will never be swap cache folio.
>
> With that changed, it looks good to me.
>
> Reviewed-by: Qu Wenruo <wqu@suse.com>
>
> Thanks,
> Qu
>
> >
> > Signed-off-by: Kairui Song <kasong@tencent.com>
> > Cc: Chris Mason <clm@fb.com> (maintainer:BTRFS FILE SYSTEM)
> > Cc: Josef Bacik <josef@toxicpanda.com> (maintainer:BTRFS FILE SYSTEM)
> > Cc: David Sterba <dsterba@suse.com> (maintainer:BTRFS FILE SYSTEM)
> > Cc: linux-btrfs@vger.kernel.org (open list:BTRFS FILE SYSTEM)
> > Signed-off-by: Kairui Song <kasong@tencent.com>
> > ---
> >   fs/btrfs/extent_io.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> > index 197f5e51c474..e08b50504d13 100644
> > --- a/fs/btrfs/extent_io.c
> > +++ b/fs/btrfs/extent_io.c
> > @@ -3509,7 +3509,7 @@ static void btree_clear_folio_dirty_tag(struct folio *folio)
> >       xa_lock_irq(&folio->mapping->i_pages);
> >       if (!folio_test_dirty(folio))
> >               __xa_clear_mark(&folio->mapping->i_pages,
> > -                             folio_index(folio), PAGECACHE_TAG_DIRTY);
> > +                             folio->index, PAGECACHE_TAG_DIRTY);
> >       xa_unlock_irq(&folio->mapping->i_pages);
> >   }
> >
>
>

[PATCH 3/6] f2fs: drop usage of folio_index

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

folio_index is only needed for mixed usage of page cache and swap
cache, for pure page cache usage, the caller can just use
folio->index instead.

It can't be a swap cache folio here.  Swap mapping may only call into fs
through `swap_rw` and that is not supported for f2fs.  So just drop it
and use folio->index instead.

Signed-off-by: Kairui Song <kasong@tencent.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org> (maintainer:F2FS FILE SYSTEM)
Cc: Chao Yu <chao@kernel.org> (maintainer:F2FS FILE SYSTEM)
Cc: linux-f2fs-devel@lists.sourceforge.net (open list:F2FS FILE SYSTEM)
Signed-off-by: Kairui Song <kasong@tencent.com>
---
 fs/f2fs/data.c   | 4 ++--
 fs/f2fs/inline.c | 4 ++--
 fs/f2fs/super.c  | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 54f89f0ee69b..5745b97ca1f0 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2077,7 +2077,7 @@ static int f2fs_read_single_page(struct inode *inode, struct folio *folio,
 	sector_t last_block;
 	sector_t last_block_in_file;
 	sector_t block_nr;
-	pgoff_t index = folio_index(folio);
+	pgoff_t index = folio->index;
 	int ret = 0;
 
 	block_in_file = (sector_t)index;
@@ -2392,7 +2392,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
 		}
 
 #ifdef CONFIG_F2FS_FS_COMPRESSION
-		index = folio_index(folio);
+		index = folio->index;
 
 		if (!f2fs_compressed_file(inode))
 			goto read_single_page;
diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
index ad92e9008781..aaaec3206538 100644
--- a/fs/f2fs/inline.c
+++ b/fs/f2fs/inline.c
@@ -86,7 +86,7 @@ void f2fs_do_read_inline_data(struct folio *folio, struct page *ipage)
 	if (folio_test_uptodate(folio))
 		return;
 
-	f2fs_bug_on(F2FS_I_SB(inode), folio_index(folio));
+	f2fs_bug_on(F2FS_I_SB(inode), folio->index);
 
 	folio_zero_segment(folio, MAX_INLINE_DATA(inode), folio_size(folio));
 
@@ -130,7 +130,7 @@ int f2fs_read_inline_data(struct inode *inode, struct folio *folio)
 		return -EAGAIN;
 	}
 
-	if (folio_index(folio))
+	if (folio->index)
 		folio_zero_segment(folio, 0, folio_size(folio));
 	else
 		f2fs_do_read_inline_data(folio, ipage);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index f087b2b71c89..eac1dcb44637 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -3432,7 +3432,7 @@ static int __f2fs_commit_super(struct f2fs_sb_info *sbi, struct folio *folio,
 	bio = bio_alloc(sbi->sb->s_bdev, 1, opf, GFP_NOFS);
 
 	/* it doesn't need to set crypto context for superblock update */
-	bio->bi_iter.bi_sector = SECTOR_FROM_BLOCK(folio_index(folio));
+	bio->bi_iter.bi_sector = SECTOR_FROM_BLOCK(folio->index);
 
 	if (!bio_add_folio(bio, folio, folio_size(folio), 0))
 		f2fs_bug_on(sbi, 1);
-- 
2.49.0

Re: [PATCH 3/6] f2fs: drop usage of folio_index

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:05AM +0800, Kairui Song wrote:
> folio_index is only needed for mixed usage of page cache and swap
> cache, for pure page cache usage, the caller can just use
> folio->index instead.
> 
> It can't be a swap cache folio here.  Swap mapping may only call into fs
> through `swap_rw` and that is not supported for f2fs.  So just drop it
> and use folio->index instead.
> 
> Signed-off-by: Kairui Song <kasong@tencent.com>
> Cc: Jaegeuk Kim <jaegeuk@kernel.org> (maintainer:F2FS FILE SYSTEM)
> Cc: Chao Yu <chao@kernel.org> (maintainer:F2FS FILE SYSTEM)
> Cc: linux-f2fs-devel@lists.sourceforge.net (open list:F2FS FILE SYSTEM)
> Signed-off-by: Kairui Song <kasong@tencent.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

> @@ -130,7 +130,7 @@ int f2fs_read_inline_data(struct inode *inode, struct folio *folio)
>  		return -EAGAIN;
>  	}
>  
> -	if (folio_index(folio))
> +	if (folio->index)
>  		folio_zero_segment(folio, 0, folio_size(folio));
>  	else
>  		f2fs_do_read_inline_data(folio, ipage);

This hunk is going to conflict with a pair of patches I sent to f2fs-devel
a few weeks ago.  I don't think there's any escaping it, just a heads-up.

Re: [PATCH 3/6] f2fs: drop usage of folio_index

[Kairui Song]

On Mon, Apr 28, 2025 at 8:41 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Apr 28, 2025 at 02:59:05AM +0800, Kairui Song wrote:
> > folio_index is only needed for mixed usage of page cache and swap
> > cache, for pure page cache usage, the caller can just use
> > folio->index instead.
> >
> > It can't be a swap cache folio here.  Swap mapping may only call into fs
> > through `swap_rw` and that is not supported for f2fs.  So just drop it
> > and use folio->index instead.
> >
> > Signed-off-by: Kairui Song <kasong@tencent.com>
> > Cc: Jaegeuk Kim <jaegeuk@kernel.org> (maintainer:F2FS FILE SYSTEM)
> > Cc: Chao Yu <chao@kernel.org> (maintainer:F2FS FILE SYSTEM)
> > Cc: linux-f2fs-devel@lists.sourceforge.net (open list:F2FS FILE SYSTEM)
> > Signed-off-by: Kairui Song <kasong@tencent.com>
>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>
> > @@ -130,7 +130,7 @@ int f2fs_read_inline_data(struct inode *inode, struct folio *folio)
> >               return -EAGAIN;
> >       }
> >
> > -     if (folio_index(folio))
> > +     if (folio->index)
> >               folio_zero_segment(folio, 0, folio_size(folio));
> >       else
> >               f2fs_do_read_inline_data(folio, ipage);
>
> This hunk is going to conflict with a pair of patches I sent to f2fs-devel
> a few weeks ago.  I don't think there's any escaping it, just a heads-up.
>

Thanks for the info, this patch is just converting folio_index to
folio->index so conflict should be easy to resolve I think? I can do a
rebase later if that series is merged first.

Re: [f2fs-dev] [PATCH 3/6] f2fs: drop usage of folio_index

[patchwork-bot+f2fs]

Hello:

This patch was applied to jaegeuk/f2fs.git (dev)
by Andrew Morton <akpm@linux-foundation.org>:

On Mon, 28 Apr 2025 02:59:05 +0800 you wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> folio_index is only needed for mixed usage of page cache and swap
> cache, for pure page cache usage, the caller can just use
> folio->index instead.
> 
> It can't be a swap cache folio here.  Swap mapping may only call into fs
> through `swap_rw` and that is not supported for f2fs.  So just drop it
> and use folio->index instead.
> 
> [...]

Here is the summary with links:
  - [f2fs-dev,3/6] f2fs: drop usage of folio_index
    https://git.kernel.org/jaegeuk/f2fs/c/fe15ec046431

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

[PATCH 4/6] filemap: do not use folio_contains for swap cache folios

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

Currently, none of the folio_contains callers will encounter swap
cache folios.

For fs/ callers, swap cache folios are never part of their workflow.

For filemap and truncate, folio_contains is only used for sanity checks
to verify the folio index matches the expected lookup/invalidation target.
The swap cache does not utilize filemap or truncate helpers in ways that
would trigger these checks, as it mostly implements its own cache management.

Shmem won't interact with these sanity checks either unless thing went
wrong, it would directly trigger a BUG, because swap cache index are
unrelated to shmem index, and would almost certainly mismatch (unless
on collide).

While some filemap helpers works for swap cache space, the swap cache
is different from the page cache in many ways. So this helper will
unlikely to work in a helpful way for swap cache folios.

So make it explicit here that folio_contains should not be used for
swap cache folios. This helps to avoid misuse and remove the folio_index
usage here.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 include/linux/pagemap.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index af25fb640463..a0bed4568c66 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -935,14 +935,14 @@ static inline struct page *folio_file_page(struct folio *folio, pgoff_t index)
  * @folio: The folio.
  * @index: The page index within the file.
  *
- * Context: The caller should have the page locked in order to prevent
- * (eg) shmem from moving the page between the page cache and swap cache
- * and changing its index in the middle of the operation.
+ * Context: The caller should ensure folio->index is stable and it's
+ * not added to the swap cache.
  * Return: true or false.
  */
 static inline bool folio_contains(struct folio *folio, pgoff_t index)
 {
-	return index - folio_index(folio) < folio_nr_pages(folio);
+	VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
+	return index - folio->index < folio_nr_pages(folio);
 }
 
 unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
-- 
2.49.0

Re: [PATCH 4/6] filemap: do not use folio_contains for swap cache folios

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:06AM +0800, Kairui Song wrote:
> For filemap and truncate, folio_contains is only used for sanity checks
> to verify the folio index matches the expected lookup/invalidation target.
> The swap cache does not utilize filemap or truncate helpers in ways that
> would trigger these checks, as it mostly implements its own cache management.
> 
> Shmem won't interact with these sanity checks either unless thing went
> wrong, it would directly trigger a BUG, because swap cache index are
> unrelated to shmem index, and would almost certainly mismatch (unless
> on collide).

It does happen though.  If shmem is writing the folio to swap at the
same time that the file containing the folio is being truncated, we
can hit this.

> - * Context: The caller should have the page locked in order to prevent
> - * (eg) shmem from moving the page between the page cache and swap cache
> - * and changing its index in the middle of the operation.
> + * Context: The caller should ensure folio->index is stable and it's
> + * not added to the swap cache.

I do think we need to keep the part about the folio being locked.

Re: [PATCH 4/6] filemap: do not use folio_contains for swap cache folios

[Kairui Song]

On Mon, Apr 28, 2025 at 8:44 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Apr 28, 2025 at 02:59:06AM +0800, Kairui Song wrote:
> > For filemap and truncate, folio_contains is only used for sanity checks
> > to verify the folio index matches the expected lookup/invalidation target.
> > The swap cache does not utilize filemap or truncate helpers in ways that
> > would trigger these checks, as it mostly implements its own cache management.
> >
> > Shmem won't interact with these sanity checks either unless thing went
> > wrong, it would directly trigger a BUG, because swap cache index are
> > unrelated to shmem index, and would almost certainly mismatch (unless
> > on collide).
>
> It does happen though.  If shmem is writing the folio to swap at the
> same time that the file containing the folio is being truncated, we
> can hit this.

Thanks for the info! I didn't check it in detail because that would
likley trigger a BUG_ON but so far I didn't see any BUG_ON commit from
there.

Just checked there are two users in truncate:

One will lock the folio and check if `folio->mapping != mapping`
first, on swapout shmem removes the folio from shmem mapping so this
check will skip the folio_contains check.

Another seems might hit the check, the time window is extremely tiny
though, only if the truncate's `xa_is_value(folio)` check passed while
another CPU is running between `folio_alloc_swap` and
`shmem_delete_from_page_cache` in shmem_writepage, then the next
VM_BUG_ON_FOLIO(!folio_contains) will fail as folio is now  a
swap cache, not shmem folio anymore. Let me double check if this needs
another fix.

Re: [PATCH 4/6] filemap: do not use folio_contains for swap cache folios

[Kairui Song]

On Mon, Apr 28, 2025 at 10:58 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> On Mon, Apr 28, 2025 at 8:44 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Mon, Apr 28, 2025 at 02:59:06AM +0800, Kairui Song wrote:
> > > For filemap and truncate, folio_contains is only used for sanity checks
> > > to verify the folio index matches the expected lookup/invalidation target.
> > > The swap cache does not utilize filemap or truncate helpers in ways that
> > > would trigger these checks, as it mostly implements its own cache management.
> > >
> > > Shmem won't interact with these sanity checks either unless thing went
> > > wrong, it would directly trigger a BUG, because swap cache index are
> > > unrelated to shmem index, and would almost certainly mismatch (unless
> > > on collide).
> >
> > It does happen though.  If shmem is writing the folio to swap at the
> > same time that the file containing the folio is being truncated, we
> > can hit this.
>
> Thanks for the info! I didn't check it in detail because that would
> likley trigger a BUG_ON but so far I didn't see any BUG_ON commit from
> there.
>
> Just checked there are two users in truncate:
>
> One will lock the folio and check if `folio->mapping != mapping`
> first, on swapout shmem removes the folio from shmem mapping so this
> check will skip the folio_contains check.
>
> Another seems might hit the check, the time window is extremely tiny
> though, only if the truncate's `xa_is_value(folio)` check passed while
> another CPU is running between `folio_alloc_swap` and
> `shmem_delete_from_page_cache` in shmem_writepage, then the next
> VM_BUG_ON_FOLIO(!folio_contains) will fail as folio is now  a
> swap cache, not shmem folio anymore. Let me double check if this needs
> another fix.

Checking all the code path, shmem managed to avoid all possible ways
to call into truncate_inode_pages_range, this is the only function
that seemed may call folio_contains with a swap cache folio.
(except tiny-shmem, it uses this function directly for truncate,
we can ignore that as it's basically just ramfs).

For truncate, shmem need to either zap a whole (large) swap/folio entry,
or zero part of folio, or swapin a large folio so that part of it can be zero'ed
(using shmem_get_partial_folio), the swapin part is a bit special so
calling generic truncate helpers might cause unexpected behaviour.

Similar story for filemap lookup.

So shmem won't call into the truncate helper here that may risk
calling folio_contains with swap cache.
Even if somehow it does, this commit won't change the BUG_ON
behaviour, except now it tells the user the folio shouldn't be a swap cache
at all, instead of reporting a buggy index. So I think this commit should
be good to have to make the swap cache less exposed.

---
List of potential call chains that may call into the truncate helper
here, and not initialized from other FS / block, none will be used by
shmem.

do_dentry_open
  /* filemap_nr_thps always 0 for shmem */
  truncate_inode_pages
    truncate_inode_pages_range

dquot_disable /* No quota file for shmem */
  truncate_inode_pages
    truncate_inode_pages_range

dquot_quota_sync /* No quota file for shmem */
  truncate_inode_pages
    truncate_inode_pages_range

truncate_inode_pages_final /* Override by shmem_evict_inode */
  truncate_inode_pages
    truncate_inode_pages_range

simple_setattr /* Override by shmem_setattr */
  truncate_setsize
    truncate_pagecache
      truncate_inode_pages
        truncate_inode_pages_range

put_aio_ring_file /* AIO calls it for private file */
  truncate_setsize
    truncate_pagecache
      truncate_inode_pages
        truncate_inode_pages_range

truncate_pagecache /* No user except other fs */
  truncate_inode_pages
    truncate_inode_pages_range

truncate_pagecache_range /* No user except other fs  */
  truncate_inode_pages_range

---

invalidate_inode_pages2 /* No user except other fs */
  invalidate_inode_pages2_range

filemap_invalidate_pages /* only used by block / direct io */
  invalidate_inode_pages2_range

filemap_invalidate_inode /* No user except other fs */
  invalidate_inode_pages2_range

kiocb_invalidate_post_direct_write /* only used by block / direct io */
  invalidate_inode_pages2_range

[PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

There are no remaining users of folio_index() outside the mm subsystem.
Move it to mm/swap.h to co-locate it with swap_cache_index(), eliminating
a forward declaration, and a function call overhead.

Also remove the helper that was used to fix circular header dependency
issue.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 include/linux/pagemap.h | 20 --------------------
 mm/memfd.c              |  1 +
 mm/migrate.c            |  1 +
 mm/swap.h               | 18 ++++++++++++++++++
 mm/swapfile.c           |  6 ------
 5 files changed, 20 insertions(+), 26 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a0bed4568c66..f61fdb8e165d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -884,26 +884,6 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 			mapping_gfp_mask(mapping));
 }
 
-extern pgoff_t __folio_swap_cache_index(struct folio *folio);
-
-/**
- * folio_index - File index of a folio.
- * @folio: The folio.
- *
- * For a folio which is either in the page cache or the swap cache,
- * return its index within the address_space it belongs to.  If you know
- * the page is definitely in the page cache, you can look at the folio's
- * index directly.
- *
- * Return: The index (offset in units of pages) of a folio in its file.
- */
-static inline pgoff_t folio_index(struct folio *folio)
-{
-	if (unlikely(folio_test_swapcache(folio)))
-		return __folio_swap_cache_index(folio);
-	return folio->index;
-}
-
 /**
  * folio_next_index - Get the index of the next folio.
  * @folio: The current folio.
diff --git a/mm/memfd.c b/mm/memfd.c
index c64df1343059..ab367e61553d 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -20,6 +20,7 @@
 #include <linux/memfd.h>
 #include <linux/pid_namespace.h>
 #include <uapi/linux/memfd.h>
+#include "swap.h"
 
 /*
  * We need a tag: a new tag would expand every xa_node by 8 bytes,
diff --git a/mm/migrate.c b/mm/migrate.c
index f3ee6d8d5e2e..662e5dc44b33 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -50,6 +50,7 @@
 #include <trace/events/migrate.h>
 
 #include "internal.h"
+#include "swap.h"
 
 bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 {
diff --git a/mm/swap.h b/mm/swap.h
index 6f4a3f927edb..2f18d21c17fb 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -50,6 +50,24 @@ static inline pgoff_t swap_cache_index(swp_entry_t entry)
 	return swp_offset(entry) & SWAP_ADDRESS_SPACE_MASK;
 }
 
+/**
+ * folio_index - File index of a folio.
+ * @folio: The folio.
+ *
+ * For a folio which is either in the page cache or the swap cache,
+ * return its index within the address_space it belongs to.  If you know
+ * the page is definitely in the page cache, you can look at the folio's
+ * index directly.
+ *
+ * Return: The index (offset in units of pages) of a folio in its file.
+ */
+static inline pgoff_t folio_index(struct folio *folio)
+{
+	if (unlikely(folio_test_swapcache(folio)))
+		return swap_cache_index(folio->swap);
+	return folio->index;
+}
+
 void show_swap_cache_info(void);
 void *get_shadow_from_swap_cache(swp_entry_t entry);
 int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
diff --git a/mm/swapfile.c b/mm/swapfile.c
index e727021b8e2c..bf6c98009909 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3662,12 +3662,6 @@ struct address_space *swapcache_mapping(struct folio *folio)
 }
 EXPORT_SYMBOL_GPL(swapcache_mapping);
 
-pgoff_t __folio_swap_cache_index(struct folio *folio)
-{
-	return swap_cache_index(folio->swap);
-}
-EXPORT_SYMBOL_GPL(__folio_swap_cache_index);
-
 /*
  * add_swap_count_continuation - called when a swap count is duplicated
  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
-- 
2.49.0

Re: [PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper

[kernel test robot]

Hi Kairui,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Kairui-Song/fuse-drop-usage-of-folio_index/20250428-030234
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250427185908.90450-6-ryncsn%40gmail.com
patch subject: [PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper
config: m68k-allnoconfig (https://download.01.org/0day-ci/archive/20250428/202504280515.4WwtyfOc-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250428/202504280515.4WwtyfOc-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202504280515.4WwtyfOc-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/page-writeback.c: In function '__folio_mark_dirty':
>> mm/page-writeback.c:2767:50: error: implicit declaration of function 'folio_index'; did you mean 'folio_inode'? [-Wimplicit-function-declaration]
    2767 |                 __xa_set_mark(&mapping->i_pages, folio_index(folio),
         |                                                  ^~~~~~~~~~~
         |                                                  folio_inode
--
   mm/gup.c: In function 'memfd_pin_folios':
>> mm/gup.c:3652:49: error: implicit declaration of function 'folio_index'; did you mean 'folio_inode'? [-Wimplicit-function-declaration]
    3652 |                                     next_idx != folio_index(fbatch.folios[i]))
         |                                                 ^~~~~~~~~~~
         |                                                 folio_inode


vim +2767 mm/page-writeback.c

b9ea25152e5636 Konstantin Khlebnikov   2015-04-14  2742  
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2743) /*
dc6e0ae5b1700c Kemeng Shi              2024-04-25  2744   * Mark the folio dirty, and set it dirty in the page cache.
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2745)  *
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2746)  * If warn is true, then emit a warning if the folio is not uptodate and has
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2747)  * not been truncated.
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2748)  *
a8cd9d4ce35eae Shakeel Butt            2024-10-24  2749   * It is the caller's responsibility to prevent the folio from being truncated
a8cd9d4ce35eae Shakeel Butt            2024-10-24  2750   * while this function is in progress, although it may have been truncated
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2751)  * before this function is called.  Most callers have the folio locked.
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2752)  * A few have the folio blocked from truncation through other means (e.g.
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2753)  * zap_vma_pages() has it mapped and is holding the page table lock).
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2754)  * When called from mark_buffer_dirty(), the filesystem should hold a
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2755)  * reference to the buffer_head that is being marked dirty, which causes
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2756)  * try_to_free_buffers() to fail.
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2757)  */
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2758) void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2759) 			     int warn)
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2760) {
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2761) 	unsigned long flags;
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2762) 
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2763) 	xa_lock_irqsave(&mapping->i_pages, flags);
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2764) 	if (folio->mapping) {	/* Race with truncate? */
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2765) 		WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2766) 		folio_account_dirtied(folio, mapping);
203a3151661611 Matthew Wilcox (Oracle  2021-05-04 @2767) 		__xa_set_mark(&mapping->i_pages, folio_index(folio),
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2768) 				PAGECACHE_TAG_DIRTY);
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2769) 	}
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2770) 	xa_unlock_irqrestore(&mapping->i_pages, flags);
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2771) }
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2772) 

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper

[kernel test robot]

Hi Kairui,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Kairui-Song/fuse-drop-usage-of-folio_index/20250428-030234
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250427185908.90450-6-ryncsn%40gmail.com
patch subject: [PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper
config: arm-allnoconfig (https://download.01.org/0day-ci/archive/20250428/202504280527.sowjkuQU-lkp@intel.com/config)
compiler: clang version 21.0.0git (https://github.com/llvm/llvm-project f819f46284f2a79790038e1f6649172789734ae8)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250428/202504280527.sowjkuQU-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202504280527.sowjkuQU-lkp@intel.com/

All errors (new ones prefixed by >>):

>> mm/page-writeback.c:2767:36: error: call to undeclared function 'folio_index'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    2767 |                 __xa_set_mark(&mapping->i_pages, folio_index(folio),
         |                                                  ^
   mm/page-writeback.c:2767:36: note: did you mean 'folio_inode'?
   include/linux/pagemap.h:567:29: note: 'folio_inode' declared here
     567 | static inline struct inode *folio_inode(struct folio *folio)
         |                             ^
   mm/page-writeback.c:3047:38: error: call to undeclared function 'folio_index'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    3047 |                 __xa_clear_mark(&mapping->i_pages, folio_index(folio),
         |                                                    ^
   mm/page-writeback.c:3084:36: error: call to undeclared function 'folio_index'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    3084 |                 XA_STATE(xas, &mapping->i_pages, folio_index(folio));
         |                                                  ^
   3 errors generated.
--
>> mm/gup.c:3652:21: error: call to undeclared function 'folio_index'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    3652 |                                     next_idx != folio_index(fbatch.folios[i]))
         |                                                 ^
   mm/gup.c:3652:21: note: did you mean 'folio_inode'?
   include/linux/pagemap.h:567:29: note: 'folio_inode' declared here
     567 | static inline struct inode *folio_inode(struct folio *folio)
         |                             ^
   1 error generated.


vim +/folio_index +2767 mm/page-writeback.c

b9ea25152e5636 Konstantin Khlebnikov   2015-04-14  2742  
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2743) /*
dc6e0ae5b1700c Kemeng Shi              2024-04-25  2744   * Mark the folio dirty, and set it dirty in the page cache.
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2745)  *
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2746)  * If warn is true, then emit a warning if the folio is not uptodate and has
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2747)  * not been truncated.
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2748)  *
a8cd9d4ce35eae Shakeel Butt            2024-10-24  2749   * It is the caller's responsibility to prevent the folio from being truncated
a8cd9d4ce35eae Shakeel Butt            2024-10-24  2750   * while this function is in progress, although it may have been truncated
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2751)  * before this function is called.  Most callers have the folio locked.
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2752)  * A few have the folio blocked from truncation through other means (e.g.
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2753)  * zap_vma_pages() has it mapped and is holding the page table lock).
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2754)  * When called from mark_buffer_dirty(), the filesystem should hold a
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2755)  * reference to the buffer_head that is being marked dirty, which causes
3d84d897920c75 Matthew Wilcox (Oracle  2024-04-16  2756)  * try_to_free_buffers() to fail.
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2757)  */
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2758) void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2759) 			     int warn)
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2760) {
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2761) 	unsigned long flags;
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2762) 
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2763) 	xa_lock_irqsave(&mapping->i_pages, flags);
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2764) 	if (folio->mapping) {	/* Race with truncate? */
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2765) 		WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
203a3151661611 Matthew Wilcox (Oracle  2021-05-04  2766) 		folio_account_dirtied(folio, mapping);
203a3151661611 Matthew Wilcox (Oracle  2021-05-04 @2767) 		__xa_set_mark(&mapping->i_pages, folio_index(folio),
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2768) 				PAGECACHE_TAG_DIRTY);
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2769) 	}
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2770) 	xa_unlock_irqrestore(&mapping->i_pages, flags);
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2771) }
6e1cae881a0646 Matthew Wilcox (Oracle  2021-06-28  2772) 

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:07AM +0800, Kairui Song wrote:
> +++ b/mm/swap.h
> @@ -50,6 +50,24 @@ static inline pgoff_t swap_cache_index(swp_entry_t entry)
>  	return swp_offset(entry) & SWAP_ADDRESS_SPACE_MASK;
>  }
>  
> +/**
> + * folio_index - File index of a folio.
> + * @folio: The folio.
> + *
> + * For a folio which is either in the page cache or the swap cache,
> + * return its index within the address_space it belongs to.  If you know
> + * the page is definitely in the page cache, you can look at the folio's
> + * index directly.
> + *
> + * Return: The index (offset in units of pages) of a folio in its file.
> + */
> +static inline pgoff_t folio_index(struct folio *folio)
> +{
> +	if (unlikely(folio_test_swapcache(folio)))
> +		return swap_cache_index(folio->swap);
> +	return folio->index;
> +}

I think the build warning can be cured by moving this outside
CONFIG_SWAP

Re: [PATCH 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper

[Kairui Song]

On Mon, Apr 28, 2025 at 7:58 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Apr 28, 2025 at 02:59:07AM +0800, Kairui Song wrote:
> > +++ b/mm/swap.h
> > @@ -50,6 +50,24 @@ static inline pgoff_t swap_cache_index(swp_entry_t entry)
> >       return swp_offset(entry) & SWAP_ADDRESS_SPACE_MASK;
> >  }
> >
> > +/**
> > + * folio_index - File index of a folio.
> > + * @folio: The folio.
> > + *
> > + * For a folio which is either in the page cache or the swap cache,
> > + * return its index within the address_space it belongs to.  If you know
> > + * the page is definitely in the page cache, you can look at the folio's
> > + * index directly.
> > + *
> > + * Return: The index (offset in units of pages) of a folio in its file.
> > + */
> > +static inline pgoff_t folio_index(struct folio *folio)
> > +{
> > +     if (unlikely(folio_test_swapcache(folio)))
> > +             return swap_cache_index(folio->swap);
> > +     return folio->index;
> > +}
>
> I think the build warning can be cured by moving this outside
> CONFIG_SWAP
>

Thanks, I will fix it in V2.

[PATCH 6/6] mm, swap: remove no longer used swap mapping helper

[Kairui Song]

From: Kairui Song <kasong@tencent.com>

This helper existed to fix the circular header dependency issue
but it is no longer used, so remove it.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 include/linux/pagemap.h | 1 -
 mm/swapfile.c           | 9 ---------
 2 files changed, 10 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f61fdb8e165d..b27e369d8bd7 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -533,7 +533,6 @@ static inline void filemap_nr_thps_dec(struct address_space *mapping)
 }
 
 struct address_space *folio_mapping(struct folio *);
-struct address_space *swapcache_mapping(struct folio *);
 
 /**
  * folio_flush_mapping - Find the file mapping this folio belongs to.
diff --git a/mm/swapfile.c b/mm/swapfile.c
index bf6c98009909..1a36e1f4f198 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3653,15 +3653,6 @@ struct swap_info_struct *swp_swap_info(swp_entry_t entry)
 	return swap_type_to_swap_info(swp_type(entry));
 }
 
-/*
- * out-of-line methods to avoid include hell.
- */
-struct address_space *swapcache_mapping(struct folio *folio)
-{
-	return swp_swap_info(folio->swap)->swap_file->f_mapping;
-}
-EXPORT_SYMBOL_GPL(swapcache_mapping);
-
 /*
  * add_swap_count_continuation - called when a swap count is duplicated
  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
-- 
2.49.0

Re: [PATCH 6/6] mm, swap: remove no longer used swap mapping helper

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:08AM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> This helper existed to fix the circular header dependency issue
> but it is no longer used, so remove it.

Oh, good catch,  It became unused with my commit 0d40cfe63a2f and
I didn't notice.

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Re: [PATCH 0/6] mm, swap: clean up swap cache mapping helper

[Kairui Song]

On Mon, Apr 28, 2025 at 3:00 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> From: Kairui Song <kasong@tencent.com>
>
> This series removes usage of folio_index usage in fs/, and remove swap
> cache checking in folio_contains.
>
> Currently, the swap cache is already no longer directly exposed to fs,
> and swap cache will be more different from page cache. Clean up the
> helpers first to simplify the code and eliminate the helpers used for
> resolving circular header dependency issue between filemap and swap
> headers.
>
> Kairui Song (6):
>   fuse: drop usage of folio_index
>   btrfs: drop usage of folio_index
>   f2fs: drop usage of folio_index
>   filemap: do not use folio_contains for swap cache folios
>   mm: move folio_index to mm/swap.h and remove no longer needed helper
>   mm, swap: remove no longer used swap mapping helper
>
>  fs/btrfs/extent_io.c    |  2 +-
>  fs/f2fs/data.c          |  4 ++--
>  fs/f2fs/inline.c        |  4 ++--
>  fs/f2fs/super.c         |  2 +-
>  fs/fuse/file.c          |  4 ++--
>  include/linux/pagemap.h | 29 ++++-------------------------
>  mm/memfd.c              |  1 +
>  mm/migrate.c            |  1 +
>  mm/swap.h               | 18 ++++++++++++++++++
>  mm/swapfile.c           | 15 ---------------
>  10 files changed, 32 insertions(+), 48 deletions(-)
>
> --
> 2.49.0
>

I just realized I added duplicated Sign-off-by in a few commits, sorry about it.

Re: [PATCH 0/6] mm, swap: clean up swap cache mapping helper

[Matthew Wilcox]

On Mon, Apr 28, 2025 at 02:59:02AM +0800, Kairui Song wrote:
> This series removes usage of folio_index usage in fs/, and remove swap
> cache checking in folio_contains.

Thanks.  I've been removing them as I've come across them (eg
fcd4904e2f69), but I haven't gone all out to try to remove it
from all filesystems.