btrfs: move the delalloc range bitmap search into extent_io.c

Currently for subpage (sector size < page size) cases, we reuse subpage
locked bitmap to find out all delalloc ranges we have locked, and run
all those found ranges.

However such reuse is not perfect, e.g.:

    0       32K      64K      96K       128K
    |       |////////||///////|    |////|
                                   120K

For above range, writepage_delalloc() for page 0 will handle the range
[32K, 96k), note delalloc range can be beyond the page boundary.

But writepage_delalloc() for page 64K will only handle range [120K,
128K), as the previous run on page 0 has already handled range [64K,
96K).
Meanwhile for the writeback we should expect range [64K, 96K) to also be
locked, this leads to the mismatch from locked bitmap and delalloc
range.

This is not causing problems yet, but it's still an inconsistent
behavior.

So instead of relying on the subpage locked bitmap, move the delalloc
range search using local @delalloc_bitmap, so that we can remove the
existing btrfs_folio_find_writer_locked().

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 43 insertions, 1 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index e5075b95cfd9..40297345b89d 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1102,6 +1102,45 @@ int btrfs_read_folio(struct file *file, struct folio *folio)
 	return ret;
 }
 
+static void set_delalloc_bitmap(struct folio *folio, unsigned long *delalloc_bitmap,
+				u64 start, u32 len)
+{
+	struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
+	const u64 folio_start = folio_pos(folio);
+	unsigned int start_bit;
+	unsigned int nbits;
+
+	ASSERT(start >= folio_start && start + len <= folio_start + PAGE_SIZE);
+	start_bit = (start - folio_start) >> fs_info->sectorsize_bits;
+	nbits = len >> fs_info->sectorsize_bits;
+	ASSERT(bitmap_test_range_all_zero(delalloc_bitmap, start_bit, nbits));
+	bitmap_set(delalloc_bitmap, start_bit, nbits);
+}
+
+static bool find_next_delalloc_bitmap(struct folio *folio,
+				      unsigned long *delalloc_bitmap, u64 start,
+				      u64 *found_start, u32 *found_len)
+{
+	struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
+	const u64 folio_start = folio_pos(folio);
+	const unsigned int bitmap_size = fs_info->sectors_per_page;
+	unsigned int start_bit;
+	unsigned int first_zero;
+	unsigned int first_set;
+
+	ASSERT(start >= folio_start && start < folio_start + PAGE_SIZE);
+
+	start_bit = (start - folio_start) >> fs_info->sectorsize_bits;
+	first_set = find_next_bit(delalloc_bitmap, bitmap_size, start_bit);
+	if (first_set >= bitmap_size)
+		return false;
+
+	*found_start = folio_start + (first_set << fs_info->sectorsize_bits);
+	first_zero = find_next_zero_bit(delalloc_bitmap, bitmap_size, first_set);
+	*found_len = (first_zero - first_set) << fs_info->sectorsize_bits;
+	return true;
+}
+
 /*
  * helper for extent_writepage(), doing all of the delayed allocation setup.
  *
@@ -1121,6 +1160,7 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 	const bool is_subpage = btrfs_is_subpage(fs_info, folio->mapping);
 	const u64 page_start = folio_pos(folio);
 	const u64 page_end = page_start + folio_size(folio) - 1;
+	unsigned long delalloc_bitmap = 0;
 	/*
 	 * Save the last found delalloc end. As the delalloc end can go beyond
 	 * page boundary, thus we cannot rely on subpage bitmap to locate the
@@ -1148,6 +1188,8 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 			delalloc_start = delalloc_end + 1;
 			continue;
 		}
+		set_delalloc_bitmap(folio, &delalloc_bitmap, delalloc_start,
+				    min(delalloc_end, page_end) + 1 - delalloc_start);
 		btrfs_folio_set_writer_lock(fs_info, folio, delalloc_start,
 					    min(delalloc_end, page_end) + 1 -
 					    delalloc_start);
@@ -1175,7 +1217,7 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 			found_len = last_delalloc_end + 1 - found_start;
 			found = true;
 		} else {
-			found = btrfs_subpage_find_writer_locked(fs_info, folio,
+			found = find_next_delalloc_bitmap(folio, &delalloc_bitmap,
 					delalloc_start, &found_start, &found_len);
 		}
 		if (!found)