[PATCH 00/10] Add and use folio_next_pos()

[PATCH 00/10] Add and use folio_next_pos()

[Matthew Wilcox (Oracle)]

It's relatively common in filesystems to want to know the end of the
current folio we're looking at.  So common in fact that btrfs has its own
helper for that.  Lift that helper to filemap and use it everywhere that
I've noticed it could be used.  This actually fixes a long-standing bug
in ocfs2 on 32-bit systems with files larger than 2GiB.  Presumably this
is not a common configuration, but I've marked it for backport anyway.

The other filesystems are all fine; none of them have a bug, they're
just mildly inefficient.  I think this should all go in via Christian's
tree, ideally with acks from the various fs maintainers (cc'd on their
individual patches).

Matthew Wilcox (Oracle) (10):
  filemap: Add folio_next_pos()
  btrfs: Use folio_next_pos()
  buffer: Use folio_next_pos()
  ext4: Use folio_next_pos()
  f2fs: Use folio_next_pos()
  gfs2: Use folio_next_pos()
  iomap: Use folio_next_pos()
  netfs: Use folio_next_pos()
  xfs: Use folio_next_pos()
  mm: Use folio_next_pos()

 fs/btrfs/compression.h    |  4 ++--
 fs/btrfs/defrag.c         |  7 ++++---
 fs/btrfs/extent_io.c      | 16 ++++++++--------
 fs/btrfs/file.c           |  9 +++++----
 fs/btrfs/inode.c          | 11 ++++++-----
 fs/btrfs/misc.h           |  5 -----
 fs/btrfs/ordered-data.c   |  2 +-
 fs/btrfs/subpage.c        |  5 +++--
 fs/buffer.c               |  2 +-
 fs/ext4/inode.c           | 10 +++++-----
 fs/f2fs/compress.c        |  2 +-
 fs/gfs2/aops.c            |  3 +--
 fs/iomap/buffered-io.c    | 10 ++++------
 fs/netfs/buffered_write.c |  2 +-
 fs/netfs/misc.c           |  2 +-
 fs/ocfs2/alloc.c          |  2 +-
 fs/xfs/scrub/xfarray.c    |  2 +-
 fs/xfs/xfs_aops.c         |  2 +-
 include/linux/pagemap.h   | 11 +++++++++++
 mm/shmem.c                |  2 +-
 mm/truncate.c             |  2 +-
 21 files changed, 59 insertions(+), 52 deletions(-)

-- 
2.47.2

[PATCH 01/10] filemap: Add folio_next_pos()

[Matthew Wilcox (Oracle)]

Replace the open-coded implementation in ocfs2 (which loses the top
32 bits on 32-bit architectures) with a helper in pagemap.h.

Fixes: 35edec1d52c0 (ocfs2: update truncate handling of partial clusters)
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: ocfs2-devel@lists.linux.dev
---
 fs/ocfs2/alloc.c        |  2 +-
 include/linux/pagemap.h | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 162711cc5b20..b267ec580da9 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -6892,7 +6892,7 @@ static void ocfs2_zero_cluster_folios(struct inode *inode, loff_t start,
 		ocfs2_map_and_dirty_folio(inode, handle, from, to, folio, 1,
 				&phys);
 
-		start = folio_next_index(folio) << PAGE_SHIFT;
+		start = folio_next_pos(folio);
 	}
 out:
 	if (folios)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 09b581c1d878..e16576e3763a 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -941,6 +941,17 @@ static inline pgoff_t folio_next_index(const struct folio *folio)
 	return folio->index + folio_nr_pages(folio);
 }
 
+/**
+ * folio_next_pos - Get the file position of the next folio.
+ * @folio: The current folio.
+ *
+ * Return: The position of the folio which follows this folio in the file.
+ */
+static inline loff_t folio_next_pos(const struct folio *folio)
+{
+	return (loff_t)folio_next_index(folio) << PAGE_SHIFT;
+}
+
 /**
  * folio_file_page - The page for a particular index.
  * @folio: The folio which contains this index.
-- 
2.47.2

Re: [PATCH 01/10] filemap: Add folio_next_pos()

[Christoph Hellwig]

On Fri, Oct 24, 2025 at 06:08:09PM +0100, Matthew Wilcox (Oracle) wrote:
> Replace the open-coded implementation in ocfs2 (which loses the top
> 32 bits on 32-bit architectures) with a helper in pagemap.h.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 01/10] filemap: Add folio_next_pos()

[Joseph Qi]

On 2025/10/25 01:08, Matthew Wilcox (Oracle) wrote:
> Replace the open-coded implementation in ocfs2 (which loses the top
> 32 bits on 32-bit architectures) with a helper in pagemap.h.
> 
> Fixes: 35edec1d52c0 (ocfs2: update truncate handling of partial clusters)
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Mark Fasheh <mark@fasheh.com>
> Cc: Joel Becker <jlbec@evilplan.org>
> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
> Cc: ocfs2-devel@lists.linux.dev

Looks fine.
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>

> ---
>  fs/ocfs2/alloc.c        |  2 +-
>  include/linux/pagemap.h | 11 +++++++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index 162711cc5b20..b267ec580da9 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -6892,7 +6892,7 @@ static void ocfs2_zero_cluster_folios(struct inode *inode, loff_t start,
>  		ocfs2_map_and_dirty_folio(inode, handle, from, to, folio, 1,
>  				&phys);
>  
> -		start = folio_next_index(folio) << PAGE_SHIFT;
> +		start = folio_next_pos(folio);
>  	}
>  out:
>  	if (folios)
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 09b581c1d878..e16576e3763a 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -941,6 +941,17 @@ static inline pgoff_t folio_next_index(const struct folio *folio)
>  	return folio->index + folio_nr_pages(folio);
>  }
>  
> +/**
> + * folio_next_pos - Get the file position of the next folio.
> + * @folio: The current folio.
> + *
> + * Return: The position of the folio which follows this folio in the file.
> + */
> +static inline loff_t folio_next_pos(const struct folio *folio)
> +{
> +	return (loff_t)folio_next_index(folio) << PAGE_SHIFT;
> +}
> +
>  /**
>   * folio_file_page - The page for a particular index.
>   * @folio: The folio which contains this index.

[PATCH 02/10] btrfs: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

btrfs defined its own variant of folio_next_pos() called folio_end().
This is an ambiguous name as 'end' might be exclusive or inclusive.
Switch to the new folio_next_pos().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Chris Mason <clm@fb.com>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
---
 fs/btrfs/compression.h  |  4 ++--
 fs/btrfs/defrag.c       |  7 ++++---
 fs/btrfs/extent_io.c    | 16 ++++++++--------
 fs/btrfs/file.c         |  9 +++++----
 fs/btrfs/inode.c        | 11 ++++++-----
 fs/btrfs/misc.h         |  5 -----
 fs/btrfs/ordered-data.c |  2 +-
 fs/btrfs/subpage.c      |  5 +++--
 8 files changed, 29 insertions(+), 30 deletions(-)

diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index eba188a9e3bb..aee1fd21cdd6 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -85,8 +85,8 @@ static inline u32 btrfs_calc_input_length(struct folio *folio, u64 range_end, u6
 {
 	/* @cur must be inside the folio. */
 	ASSERT(folio_pos(folio) <= cur);
-	ASSERT(cur < folio_end(folio));
-	return min(range_end, folio_end(folio)) - cur;
+	ASSERT(cur < folio_next_pos(folio));
+	return umin(range_end, folio_next_pos(folio)) - cur;
 }
 
 int btrfs_alloc_compress_wsm(struct btrfs_fs_info *fs_info);
diff --git a/fs/btrfs/defrag.c b/fs/btrfs/defrag.c
index 7b277934f66f..8fb353feacc9 100644
--- a/fs/btrfs/defrag.c
+++ b/fs/btrfs/defrag.c
@@ -886,7 +886,7 @@ static struct folio *defrag_prepare_one_folio(struct btrfs_inode *inode, pgoff_t
 	}
 
 	lock_start = folio_pos(folio);
-	lock_end = folio_end(folio) - 1;
+	lock_end = folio_next_pos(folio) - 1;
 	/* Wait for any existing ordered extent in the range */
 	while (1) {
 		struct btrfs_ordered_extent *ordered;
@@ -1178,7 +1178,8 @@ static int defrag_one_locked_target(struct btrfs_inode *inode,
 
 		if (!folio)
 			break;
-		if (start >= folio_end(folio) || start + len <= folio_pos(folio))
+		if (start >= folio_next_pos(folio) ||
+		    start + len <= folio_pos(folio))
 			continue;
 		btrfs_folio_clamp_clear_checked(fs_info, folio, start, len);
 		btrfs_folio_clamp_set_dirty(fs_info, folio, start, len);
@@ -1219,7 +1220,7 @@ static int defrag_one_range(struct btrfs_inode *inode, u64 start, u32 len,
 			folios[i] = NULL;
 			goto free_folios;
 		}
-		cur = folio_end(folios[i]);
+		cur = folio_next_pos(folios[i]);
 	}
 	for (int i = 0; i < nr_pages; i++) {
 		if (!folios[i])
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 755ec6dfd51c..ac1550739eb3 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -333,7 +333,7 @@ static noinline int lock_delalloc_folios(struct inode *inode,
 				goto out;
 			}
 			range_start = max_t(u64, folio_pos(folio), start);
-			range_len = min_t(u64, folio_end(folio), end + 1) - range_start;
+			range_len = min_t(u64, folio_next_pos(folio), end + 1) - range_start;
 			btrfs_folio_set_lock(fs_info, folio, range_start, range_len);
 
 			processed_end = range_start + range_len - 1;
@@ -387,7 +387,7 @@ noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
 	ASSERT(orig_end > orig_start);
 
 	/* The range should at least cover part of the folio */
-	ASSERT(!(orig_start >= folio_end(locked_folio) ||
+	ASSERT(!(orig_start >= folio_next_pos(locked_folio) ||
 		 orig_end <= folio_pos(locked_folio)));
 again:
 	/* step one, find a bunch of delalloc bytes starting at start */
@@ -493,7 +493,7 @@ static void end_folio_read(struct folio *folio, bool uptodate, u64 start, u32 le
 	struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
 
 	ASSERT(folio_pos(folio) <= start &&
-	       start + len <= folio_end(folio));
+	       start + len <= folio_next_pos(folio));
 
 	if (uptodate && btrfs_verify_folio(folio, start, len))
 		btrfs_folio_set_uptodate(fs_info, folio, start, len);
@@ -1201,7 +1201,7 @@ static bool can_skip_one_ordered_range(struct btrfs_inode *inode,
 	 * finished our folio read and unlocked the folio.
 	 */
 	if (btrfs_folio_test_dirty(fs_info, folio, cur, blocksize)) {
-		u64 range_len = min(folio_end(folio),
+		u64 range_len = umin(folio_next_pos(folio),
 				    ordered->file_offset + ordered->num_bytes) - cur;
 
 		ret = true;
@@ -1223,7 +1223,7 @@ static bool can_skip_one_ordered_range(struct btrfs_inode *inode,
 	 * So we return true and update @next_ret to the OE/folio boundary.
 	 */
 	if (btrfs_folio_test_uptodate(fs_info, folio, cur, blocksize)) {
-		u64 range_len = min(folio_end(folio),
+		u64 range_len = umin(folio_next_pos(folio),
 				    ordered->file_offset + ordered->num_bytes) - cur;
 
 		/*
@@ -2215,7 +2215,7 @@ static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
 	for (int i = 0; i < num_extent_folios(eb); i++) {
 		struct folio *folio = eb->folios[i];
 		u64 range_start = max_t(u64, eb->start, folio_pos(folio));
-		u32 range_len = min_t(u64, folio_end(folio),
+		u32 range_len = min_t(u64, folio_next_pos(folio),
 				      eb->start + eb->len) - range_start;
 
 		folio_lock(folio);
@@ -2619,7 +2619,7 @@ void extent_write_locked_range(struct inode *inode, const struct folio *locked_f
 			continue;
 		}
 
-		cur_end = min_t(u64, folio_end(folio) - 1, end);
+		cur_end = min_t(u64, folio_next_pos(folio) - 1, end);
 		cur_len = cur_end + 1 - cur;
 
 		ASSERT(folio_test_locked(folio));
@@ -3860,7 +3860,7 @@ int read_extent_buffer_pages_nowait(struct extent_buffer *eb, int mirror_num,
 	for (int i = 0; i < num_extent_folios(eb); i++) {
 		struct folio *folio = eb->folios[i];
 		u64 range_start = max_t(u64, eb->start, folio_pos(folio));
-		u32 range_len = min_t(u64, folio_end(folio),
+		u32 range_len = min_t(u64, folio_next_pos(folio),
 				      eb->start + eb->len) - range_start;
 
 		bio_add_folio_nofail(&bbio->bio, folio, range_len,
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 7efd1f8a1912..977931cfa71e 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -89,7 +89,8 @@ int btrfs_dirty_folio(struct btrfs_inode *inode, struct folio *folio, loff_t pos
 	num_bytes = round_up(write_bytes + pos - start_pos,
 			     fs_info->sectorsize);
 	ASSERT(num_bytes <= U32_MAX);
-	ASSERT(folio_pos(folio) <= pos && folio_end(folio) >= pos + write_bytes);
+	ASSERT(folio_pos(folio) <= pos &&
+	       folio_next_pos(folio) >= pos + write_bytes);
 
 	end_of_last_block = start_pos + num_bytes - 1;
 
@@ -799,7 +800,7 @@ static int prepare_uptodate_folio(struct inode *inode, struct folio *folio, u64
 				  u64 len)
 {
 	u64 clamp_start = max_t(u64, pos, folio_pos(folio));
-	u64 clamp_end = min_t(u64, pos + len, folio_end(folio));
+	u64 clamp_end = min_t(u64, pos + len, folio_next_pos(folio));
 	const u32 blocksize = inode_to_fs_info(inode)->sectorsize;
 	int ret = 0;
 
@@ -1254,8 +1255,8 @@ static int copy_one_range(struct btrfs_inode *inode, struct iov_iter *iter,
 	 * The reserved range goes beyond the current folio, shrink the reserved
 	 * space to the folio boundary.
 	 */
-	if (reserved_start + reserved_len > folio_end(folio)) {
-		const u64 last_block = folio_end(folio);
+	if (reserved_start + reserved_len > folio_next_pos(folio)) {
+		const u64 last_block = folio_next_pos(folio);
 
 		shrink_reserved_space(inode, *data_reserved, reserved_start,
 				      reserved_len, last_block - reserved_start,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3b1b3a0553ee..b7b498fffa4f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -409,7 +409,7 @@ static inline void btrfs_cleanup_ordered_extents(struct btrfs_inode *inode,
 			continue;
 		}
 
-		index = folio_end(folio) >> PAGE_SHIFT;
+		index = folio_next_index(folio);
 		/*
 		 * Here we just clear all Ordered bits for every page in the
 		 * range, then btrfs_mark_ordered_io_finished() will handle
@@ -2336,7 +2336,8 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
 	 * The range must cover part of the @locked_folio, or a return of 1
 	 * can confuse the caller.
 	 */
-	ASSERT(!(end <= folio_pos(locked_folio) || start >= folio_end(locked_folio)));
+	ASSERT(!(end <= folio_pos(locked_folio) ||
+		 start >= folio_next_pos(locked_folio)));
 
 	if (should_nocow(inode, start, end)) {
 		ret = run_delalloc_nocow(inode, locked_folio, start, end);
@@ -2743,7 +2744,7 @@ static void btrfs_writepage_fixup_worker(struct btrfs_work *work)
 	struct btrfs_inode *inode = fixup->inode;
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
 	u64 page_start = folio_pos(folio);
-	u64 page_end = folio_end(folio) - 1;
+	u64 page_end = folio_next_pos(folio) - 1;
 	int ret = 0;
 	bool free_delalloc_space = true;
 
@@ -4855,7 +4856,7 @@ static int truncate_block_zero_beyond_eof(struct btrfs_inode *inode, u64 start)
 	 */
 
 	zero_start = max_t(u64, folio_pos(folio), start);
-	zero_end = folio_end(folio);
+	zero_end = folio_next_pos(folio);
 	folio_zero_range(folio, zero_start - folio_pos(folio),
 			 zero_end - zero_start);
 
@@ -5038,7 +5039,7 @@ int btrfs_truncate_block(struct btrfs_inode *inode, u64 offset, u64 start, u64 e
 		 * not reach disk, it still affects our page caches.
 		 */
 		zero_start = max_t(u64, folio_pos(folio), start);
-		zero_end = min_t(u64, folio_end(folio) - 1, end);
+		zero_end = min_t(u64, folio_next_pos(folio) - 1, end);
 	} else {
 		zero_start = max_t(u64, block_start, start);
 		zero_end = min_t(u64, block_end, end);
diff --git a/fs/btrfs/misc.h b/fs/btrfs/misc.h
index 60f9b000d644..17b71e1285e5 100644
--- a/fs/btrfs/misc.h
+++ b/fs/btrfs/misc.h
@@ -209,9 +209,4 @@ static inline bool bitmap_test_range_all_zero(const unsigned long *addr,
 	return (found_set == start + nbits);
 }
 
-static inline u64 folio_end(struct folio *folio)
-{
-	return folio_pos(folio) + folio_size(folio);
-}
-
 #endif
diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 2829f20d7bb5..7fedebbee558 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -359,7 +359,7 @@ static bool can_finish_ordered_extent(struct btrfs_ordered_extent *ordered,
 	if (folio) {
 		ASSERT(folio->mapping);
 		ASSERT(folio_pos(folio) <= file_offset);
-		ASSERT(file_offset + len <= folio_end(folio));
+		ASSERT(file_offset + len <= folio_next_pos(folio));
 
 		/*
 		 * Ordered flag indicates whether we still have
diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 5ca8d4db6722..a7ba868e9372 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -186,7 +186,8 @@ static void btrfs_subpage_assert(const struct btrfs_fs_info *fs_info,
 	 * unmapped page like dummy extent buffer pages.
 	 */
 	if (folio->mapping)
-		ASSERT(folio_pos(folio) <= start && start + len <= folio_end(folio),
+		ASSERT(folio_pos(folio) <= start &&
+		       start + len <= folio_next_pos(folio),
 		       "start=%llu len=%u folio_pos=%llu folio_size=%zu",
 		       start, len, folio_pos(folio), folio_size(folio));
 }
@@ -217,7 +218,7 @@ static void btrfs_subpage_clamp_range(struct folio *folio, u64 *start, u32 *len)
 	if (folio_pos(folio) >= orig_start + orig_len)
 		*len = 0;
 	else
-		*len = min_t(u64, folio_end(folio), orig_start + orig_len) - *start;
+		*len = min_t(u64, folio_next_pos(folio), orig_start + orig_len) - *start;
 }
 
 static bool btrfs_subpage_end_and_test_lock(const struct btrfs_fs_info *fs_info,
-- 
2.47.2

Re: [PATCH 02/10] btrfs: Use folio_next_pos()

[David Sterba]

On Fri, Oct 24, 2025 at 06:08:10PM +0100, Matthew Wilcox (Oracle) wrote:
> btrfs defined its own variant of folio_next_pos() called folio_end().
> This is an ambiguous name as 'end' might be exclusive or inclusive.
> Switch to the new folio_next_pos().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Chris Mason <clm@fb.com>
> Cc: David Sterba <dsterba@suse.com>

Acked-by: David Sterba <dsterba@suse.com>

[PATCH 03/10] buffer: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
---
 fs/buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 6a8752f7bbed..185ceb0d6baa 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2732,7 +2732,7 @@ int block_write_full_folio(struct folio *folio, struct writeback_control *wbc,
 	loff_t i_size = i_size_read(inode);
 
 	/* Is the folio fully inside i_size? */
-	if (folio_pos(folio) + folio_size(folio) <= i_size)
+	if (folio_next_pos(folio) <= i_size)
 		return __block_write_full_folio(inode, folio, get_block, wbc);
 
 	/* Is the folio fully outside i_size? (truncate in progress) */
-- 
2.47.2

Re: [PATCH 03/10] buffer: Use folio_next_pos()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 03/10] buffer: Use folio_next_pos()

[Jan Kara]

On Fri 24-10-25 18:08:11, Matthew Wilcox (Oracle) wrote:
> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Jan Kara <jack@suse.cz>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/buffer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 6a8752f7bbed..185ceb0d6baa 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2732,7 +2732,7 @@ int block_write_full_folio(struct folio *folio, struct writeback_control *wbc,
>  	loff_t i_size = i_size_read(inode);
>  
>  	/* Is the folio fully inside i_size? */
> -	if (folio_pos(folio) + folio_size(folio) <= i_size)
> +	if (folio_next_pos(folio) <= i_size)
>  		return __block_write_full_folio(inode, folio, get_block, wbc);
>  
>  	/* Is the folio fully outside i_size? (truncate in progress) */
> -- 
> 2.47.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

[PATCH 04/10] ext4: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: linux-ext4@vger.kernel.org
---
 fs/ext4/inode.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e99306a8f47c..1b22e9516db4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1319,8 +1319,8 @@ static int ext4_write_begin(const struct kiocb *iocb,
 	if (IS_ERR(folio))
 		return PTR_ERR(folio);
 
-	if (pos + len > folio_pos(folio) + folio_size(folio))
-		len = folio_pos(folio) + folio_size(folio) - pos;
+	if (len > folio_next_pos(folio) - pos)
+		len = folio_next_pos(folio) - pos;
 
 	from = offset_in_folio(folio, pos);
 	to = from + len;
@@ -2704,7 +2704,7 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 
 			if (mpd->map.m_len == 0)
 				mpd->start_pos = folio_pos(folio);
-			mpd->next_pos = folio_pos(folio) + folio_size(folio);
+			mpd->next_pos = folio_next_pos(folio);
 			/*
 			 * Writeout when we cannot modify metadata is simple.
 			 * Just submit the page. For data=journal mode we
@@ -3146,8 +3146,8 @@ static int ext4_da_write_begin(const struct kiocb *iocb,
 	if (IS_ERR(folio))
 		return PTR_ERR(folio);
 
-	if (pos + len > folio_pos(folio) + folio_size(folio))
-		len = folio_pos(folio) + folio_size(folio) - pos;
+	if (len > folio_next_pos(folio) - pos)
+		len = folio_next_pos(folio) - pos;
 
 	ret = ext4_block_write_begin(NULL, folio, pos, len,
 				     ext4_da_get_block_prep);
-- 
2.47.2

Re: [PATCH 04/10] ext4: Use folio_next_pos()

[Zhang Yi]

On 10/25/2025 1:08 AM, Matthew Wilcox (Oracle) wrote:
> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: linux-ext4@vger.kernel.org

A nice cleanup!

Reviewed-by: Zhang Yi <yi.zhang@huawei.com>

> ---
>  fs/ext4/inode.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e99306a8f47c..1b22e9516db4 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1319,8 +1319,8 @@ static int ext4_write_begin(const struct kiocb *iocb,
>  	if (IS_ERR(folio))
>  		return PTR_ERR(folio);
>  
> -	if (pos + len > folio_pos(folio) + folio_size(folio))
> -		len = folio_pos(folio) + folio_size(folio) - pos;
> +	if (len > folio_next_pos(folio) - pos)
> +		len = folio_next_pos(folio) - pos;
>  
>  	from = offset_in_folio(folio, pos);
>  	to = from + len;
> @@ -2704,7 +2704,7 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
>  
>  			if (mpd->map.m_len == 0)
>  				mpd->start_pos = folio_pos(folio);
> -			mpd->next_pos = folio_pos(folio) + folio_size(folio);
> +			mpd->next_pos = folio_next_pos(folio);
>  			/*
>  			 * Writeout when we cannot modify metadata is simple.
>  			 * Just submit the page. For data=journal mode we
> @@ -3146,8 +3146,8 @@ static int ext4_da_write_begin(const struct kiocb *iocb,
>  	if (IS_ERR(folio))
>  		return PTR_ERR(folio);
>  
> -	if (pos + len > folio_pos(folio) + folio_size(folio))
> -		len = folio_pos(folio) + folio_size(folio) - pos;
> +	if (len > folio_next_pos(folio) - pos)
> +		len = folio_next_pos(folio) - pos;
>  
>  	ret = ext4_block_write_begin(NULL, folio, pos, len,
>  				     ext4_da_get_block_prep);

Re: [PATCH 04/10] ext4: Use folio_next_pos()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH 05/10] f2fs: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Chao Yu <chao@kernel.org>
Cc: linux-f2fs-devel@lists.sourceforge.net
---
 fs/f2fs/compress.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 6ad8d3bc6df7..be53e06caf3d 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1329,7 +1329,7 @@ static int f2fs_write_compressed_pages(struct compress_ctx *cc,
 	}
 
 	folio = page_folio(cc->rpages[last_index]);
-	psize = folio_pos(folio) + folio_size(folio);
+	psize = folio_next_pos(folio);
 
 	err = f2fs_get_node_info(fio.sbi, dn.nid, &ni, false);
 	if (err)
-- 
2.47.2

Re: [PATCH 05/10] f2fs: Use folio_next_pos()

[Chao Yu]

On 10/25/25 01:08, Matthew Wilcox (Oracle) wrote:
> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Jaegeuk Kim <jaegeuk@kernel.org>
> Cc: Chao Yu <chao@kernel.org>
> Cc: linux-f2fs-devel@lists.sourceforge.net

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

[PATCH 06/10] gfs2: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: gfs2@lists.linux.dev
---
 fs/gfs2/aops.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 47d74afd63ac..d8ba97bad8bb 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -81,8 +81,7 @@ static int gfs2_write_jdata_folio(struct folio *folio,
 	 * the page size, the remaining memory is zeroed when mapped, and
 	 * writes to that region are not written out to the file."
 	 */
-	if (folio_pos(folio) < i_size &&
-	    i_size < folio_pos(folio) + folio_size(folio))
+	if (folio_pos(folio) < i_size && i_size < folio_next_pos(folio))
 		folio_zero_segment(folio, offset_in_folio(folio, i_size),
 				folio_size(folio));
 
-- 
2.47.2

[PATCH 07/10] iomap: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org
---
 fs/iomap/buffered-io.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 8b847a1e27f1..32a27f36372d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -707,7 +707,7 @@ static int __iomap_write_begin(const struct iomap_iter *iter,
 	 * are not changing pagecache contents.
 	 */
 	if (!(iter->flags & IOMAP_UNSHARE) && pos <= folio_pos(folio) &&
-	    pos + len >= folio_pos(folio) + folio_size(folio))
+	    pos + len >= folio_next_pos(folio))
 		return 0;
 
 	ifs = ifs_alloc(iter->inode, folio, iter->flags);
@@ -1097,8 +1097,7 @@ static void iomap_write_delalloc_ifs_punch(struct inode *inode,
 	if (!ifs)
 		return;
 
-	last_byte = min_t(loff_t, end_byte - 1,
-			folio_pos(folio) + folio_size(folio) - 1);
+	last_byte = min_t(loff_t, end_byte - 1, folio_next_pos(folio) - 1);
 	first_blk = offset_in_folio(folio, start_byte) >> blkbits;
 	last_blk = offset_in_folio(folio, last_byte) >> blkbits;
 	for (i = first_blk; i <= last_blk; i++) {
@@ -1129,8 +1128,7 @@ static void iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
 	 * Make sure the next punch start is correctly bound to
 	 * the end of this data range, not the end of the folio.
 	 */
-	*punch_start_byte = min_t(loff_t, end_byte,
-				folio_pos(folio) + folio_size(folio));
+	*punch_start_byte = min_t(loff_t, end_byte, folio_next_pos(folio));
 }
 
 /*
@@ -1170,7 +1168,7 @@ static void iomap_write_delalloc_scan(struct inode *inode,
 				start_byte, end_byte, iomap, punch);
 
 		/* move offset to start of next folio in range */
-		start_byte = folio_pos(folio) + folio_size(folio);
+		start_byte = folio_next_pos(folio);
 		folio_unlock(folio);
 		folio_put(folio);
 	}
-- 
2.47.2

Re: [PATCH 07/10] iomap: Use folio_next_pos()

[Darrick J. Wong]

On Fri, Oct 24, 2025 at 06:08:15PM +0100, Matthew Wilcox (Oracle) wrote:
> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: "Darrick J. Wong" <djwong@kernel.org>
> Cc: linux-xfs@vger.kernel.org

Looks like a nice win, even if a small one
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/iomap/buffered-io.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 8b847a1e27f1..32a27f36372d 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -707,7 +707,7 @@ static int __iomap_write_begin(const struct iomap_iter *iter,
>  	 * are not changing pagecache contents.
>  	 */
>  	if (!(iter->flags & IOMAP_UNSHARE) && pos <= folio_pos(folio) &&
> -	    pos + len >= folio_pos(folio) + folio_size(folio))
> +	    pos + len >= folio_next_pos(folio))
>  		return 0;
>  
>  	ifs = ifs_alloc(iter->inode, folio, iter->flags);
> @@ -1097,8 +1097,7 @@ static void iomap_write_delalloc_ifs_punch(struct inode *inode,
>  	if (!ifs)
>  		return;
>  
> -	last_byte = min_t(loff_t, end_byte - 1,
> -			folio_pos(folio) + folio_size(folio) - 1);
> +	last_byte = min_t(loff_t, end_byte - 1, folio_next_pos(folio) - 1);
>  	first_blk = offset_in_folio(folio, start_byte) >> blkbits;
>  	last_blk = offset_in_folio(folio, last_byte) >> blkbits;
>  	for (i = first_blk; i <= last_blk; i++) {
> @@ -1129,8 +1128,7 @@ static void iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
>  	 * Make sure the next punch start is correctly bound to
>  	 * the end of this data range, not the end of the folio.
>  	 */
> -	*punch_start_byte = min_t(loff_t, end_byte,
> -				folio_pos(folio) + folio_size(folio));
> +	*punch_start_byte = min_t(loff_t, end_byte, folio_next_pos(folio));
>  }
>  
>  /*
> @@ -1170,7 +1168,7 @@ static void iomap_write_delalloc_scan(struct inode *inode,
>  				start_byte, end_byte, iomap, punch);
>  
>  		/* move offset to start of next folio in range */
> -		start_byte = folio_pos(folio) + folio_size(folio);
> +		start_byte = folio_next_pos(folio);
>  		folio_unlock(folio);
>  		folio_put(folio);
>  	}
> -- 
> 2.47.2
> 

Re: [PATCH 07/10] iomap: Use folio_next_pos()

[Christoph Hellwig]

On Fri, Oct 24, 2025 at 06:08:15PM +0100, Matthew Wilcox (Oracle) wrote:
> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH 08/10] netfs: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Paulo Alcantara <pc@manguebit.org>
Cc: netfs@lists.linux.dev
---
 fs/netfs/buffered_write.c | 2 +-
 fs/netfs/misc.c           | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 09394ac2c180..f9d62abef2ac 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -535,7 +535,7 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
 		folio_unlock(folio);
 		err = filemap_fdatawrite_range(mapping,
 					       folio_pos(folio),
-					       folio_pos(folio) + folio_size(folio));
+					       folio_next_pos(folio));
 		switch (err) {
 		case 0:
 			ret = VM_FAULT_RETRY;
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index 486166460e17..82342c6d22cb 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -298,7 +298,7 @@ bool netfs_release_folio(struct folio *folio, gfp_t gfp)
 	if (folio_test_dirty(folio))
 		return false;
 
-	end = umin(folio_pos(folio) + folio_size(folio), i_size_read(&ctx->inode));
+	end = umin(folio_next_pos(folio), i_size_read(&ctx->inode));
 	if (end > ctx->zero_point)
 		ctx->zero_point = end;
 
-- 
2.47.2

Re: [PATCH 08/10] netfs: Use folio_next_pos()

[Paulo Alcantara]

"Matthew Wilcox (Oracle)" <willy@infradead.org> writes:

> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Paulo Alcantara <pc@manguebit.org>
> Cc: netfs@lists.linux.dev

Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>

[PATCH 09/10] xfs: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Carlos Maiolino <cem@kernel.org>
Cc: linux-xfs@vger.kernel.org
---
 fs/xfs/scrub/xfarray.c | 2 +-
 fs/xfs/xfs_aops.c      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/scrub/xfarray.c b/fs/xfs/scrub/xfarray.c
index cdd13ed9c569..ed2e8c64b1a8 100644
--- a/fs/xfs/scrub/xfarray.c
+++ b/fs/xfs/scrub/xfarray.c
@@ -834,7 +834,7 @@ xfarray_sort_scan(
 		si->first_folio_idx = xfarray_idx(si->array,
 				folio_pos(si->folio) + si->array->obj_size - 1);
 
-		next_pos = folio_pos(si->folio) + folio_size(si->folio);
+		next_pos = folio_next_pos(si->folio);
 		si->last_folio_idx = xfarray_idx(si->array, next_pos - 1);
 		if (xfarray_pos(si->array, si->last_folio_idx + 1) > next_pos)
 			si->last_folio_idx--;
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index a26f79815533..ad76d5d01dd1 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -271,7 +271,7 @@ xfs_discard_folio(
 	 * folio itself and not the start offset that is passed in.
 	 */
 	xfs_bmap_punch_delalloc_range(ip, XFS_DATA_FORK, pos,
-				folio_pos(folio) + folio_size(folio), NULL);
+				folio_next_pos(folio), NULL);
 }
 
 /*
-- 
2.47.2

Re: [PATCH 09/10] xfs: Use folio_next_pos()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH 10/10] mm: Use folio_next_pos()

[Matthew Wilcox (Oracle)]

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
---
 mm/shmem.c    | 2 +-
 mm/truncate.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b9081b817d28..c819cecf1ed9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1133,7 +1133,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
 	folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT);
 	if (folio) {
-		same_folio = lend < folio_pos(folio) + folio_size(folio);
+		same_folio = lend < folio_next_pos(folio);
 		folio_mark_dirty(folio);
 		if (!truncate_inode_partial_folio(folio, lstart, lend)) {
 			start = folio_next_index(folio);
diff --git a/mm/truncate.c b/mm/truncate.c
index 91eb92a5ce4f..a3d673533e32 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -387,7 +387,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
 	folio = __filemap_get_folio(mapping, lstart >> PAGE_SHIFT, FGP_LOCK, 0);
 	if (!IS_ERR(folio)) {
-		same_folio = lend < folio_pos(folio) + folio_size(folio);
+		same_folio = lend < folio_next_pos(folio);
 		if (!truncate_inode_partial_folio(folio, lstart, lend)) {
 			start = folio_next_index(folio);
 			if (same_folio)
-- 
2.47.2

Re: [PATCH 10/10] mm: Use folio_next_pos()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 10/10] mm: Use folio_next_pos()

[David Hildenbrand]

On 24.10.25 19:08, Matthew Wilcox (Oracle) wrote:
> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> ---

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb

Re: [PATCH 08/10] netfs: Use folio_next_pos()

[David Howells]

Matthew Wilcox (Oracle) <willy@infradead.org> wrote:

> This is one instruction more efficient than open-coding folio_pos() +
> folio_size().  It's the equivalent of (x + y) << z rather than
> x << z + y << z.

Should that be noted to the gcc bugzilla as a missed optimisation?

> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Paulo Alcantara <pc@manguebit.org>
> Cc: netfs@lists.linux.dev

Acked-by: David Howells <dhowells@redhat.com>

Re: [PATCH 08/10] netfs: Use folio_next_pos()

[Matthew Wilcox]

On Mon, Oct 27, 2025 at 02:16:45PM +0000, David Howells wrote:
> Matthew Wilcox (Oracle) <willy@infradead.org> wrote:
> 
> > This is one instruction more efficient than open-coding folio_pos() +
> > folio_size().  It's the equivalent of (x + y) << z rather than
> > x << z + y << z.
> 
> Should that be noted to the gcc bugzilla as a missed optimisation?

I don't know?  Maybe there's a Law Of C Arithmetic that prevents it
from doing this optimisation that we can ignore because we know that
the calculation will never overflow.

I tried with both gcc and LLVM and both produce better code for g()
than for f():
https://godbolt.org/z/YTc883f6G

Interestingly, LLVM does better for f() than gcc does, but they produce
identical code for g() (minor difference like using sal instead of shl
but that feels unimportant).

If you want to file optimisation bug(s) against gcc, feel free to use
this example code.

Re: [PATCH 00/10] Add and use folio_next_pos()

[Christian Brauner]

On Fri, 24 Oct 2025 18:08:08 +0100, Matthew Wilcox (Oracle) wrote:
> It's relatively common in filesystems to want to know the end of the
> current folio we're looking at.  So common in fact that btrfs has its own
> helper for that.  Lift that helper to filemap and use it everywhere that
> I've noticed it could be used.  This actually fixes a long-standing bug
> in ocfs2 on 32-bit systems with files larger than 2GiB.  Presumably this
> is not a common configuration, but I've marked it for backport anyway.
> 
> [...]

I'm moving this into a separate topic branch for now in case any
filesystems would like to base off of this.

---

Applied to the vfs-6.19.folio branch of the vfs/vfs.git tree.
Patches in the vfs-6.19.folio branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.19.folio

[01/10] filemap: Add folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/4511fd86db6f
[02/10] btrfs: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/48f3784b17d9
[03/10] buffer: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/6870892b6437
[04/10] ext4: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/4db47b252190
[05/10] f2fs: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/4fcafa30b70a
[06/10] gfs2: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/5f0fc785322d
[07/10] iomap: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/ac9752080475
[08/10] netfs: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/2408900d408a
[09/10] xfs: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/ac0a11113de3
[10/10] mm: Use folio_next_pos()
        https://git.kernel.org/vfs/vfs/c/60a70e61430b