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btrfs: subpage: simplify the PAGECACHE_TAG_TOWRITE handling

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In function btrfs_subpage_set_writeback() we need to keep the
PAGECACHE_TAG_TOWRITE tag if the folio is still dirty.

This is a needed quirk for support async extents, as a subpage range can
almost suddenly go writeback, without touching other subpage ranges in
the same folio.

However we can simplify the handling by replace the open-coded tag
clearing by passing the @keep_write flag depending on if the folio is
dirty.

Since we're holding the subpage lock already, no one is able to change
the dirty/writeback flag, thus it's safe to check the folio dirty before
calling __folio_start_writeback().

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2025-10-21 14:21:48 +10:30 committed by David Sterba
parent ca428e9b49
commit 988f693a46
1 changed files with 3 additions and 11 deletions
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14
fs/btrfs/subpage.c
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@ -440,6 +440,7 @@ void btrfs_subpage_set_writeback(const struct btrfs_fs_info *fs_info,
unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
writeback, start, len);
unsigned long flags;
bool keep_write;
spin_lock_irqsave(&bfs->lock, flags);
bitmap_set(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
@ -450,18 +451,9 @@ void btrfs_subpage_set_writeback(const struct btrfs_fs_info *fs_info,
* assume writeback is complete, and exit too early — violating sync
* ordering guarantees.
*/
keep_write = folio_test_dirty(folio);
if (!folio_test_writeback(folio))
__folio_start_writeback(folio, true);
if (!folio_test_dirty(folio)) {
struct address_space *mapping = folio_mapping(folio);
XA_STATE(xas, &mapping->i_pages, folio->index);
unsigned long xa_flags;
xas_lock_irqsave(&xas, xa_flags);
xas_load(&xas);
xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
xas_unlock_irqrestore(&xas, xa_flags);
}
__folio_start_writeback(folio, keep_write);
spin_unlock_irqrestore(&bfs->lock, flags);
}