6.16-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo wqu@suse.com
[ Upstream commit 1e17738d6b76cdc76d240d64de87fa66ba2365f7 ]
Unlike the iomap_folio_state structure, the btrfs_subpage structure has a lot of extra sub-bitmaps, namely:
- writeback sub-bitmap - locked sub-bitmap iomap_folio_state uses an atomic for writeback tracking, while it has no per-block locked tracking.
This is because iomap always locks a single folio, and submits dirty blocks with that folio locked.
But btrfs has async delalloc ranges (for compression), which are queued with their range locked, until the compression is done, then marks the involved range writeback and unlocked.
This means a range can be unlocked and marked writeback at seemingly random timing, thus it needs the extra tracking.
This needs a huge rework on the lifespan of async delalloc range before we can remove/simplify these two sub-bitmaps.
- ordered sub-bitmap - checked sub-bitmap These are for COW-fixup, but as I mentioned in the past, the COW-fixup is not really needed anymore and these two flags are already marked deprecated, and will be removed in the near future after comprehensive tests.
Add related comments to indicate we're actively trying to align the sub-bitmaps to the iomap ones.
Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Stable-dep-of: b1511360c8ac ("btrfs: subpage: keep TOWRITE tag until folio is cleaned") Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/subpage.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
--- a/fs/btrfs/subpage.h +++ b/fs/btrfs/subpage.h @@ -33,8 +33,22 @@ enum { btrfs_bitmap_nr_uptodate = 0, btrfs_bitmap_nr_dirty, btrfs_bitmap_nr_writeback, + /* + * The ordered and checked flags are for COW fixup, already marked + * deprecated, and will be removed eventually. + */ btrfs_bitmap_nr_ordered, btrfs_bitmap_nr_checked, + + /* + * The locked bit is for async delalloc range (compression), currently + * async extent is queued with the range locked, until the compression + * is done. + * So an async extent can unlock the range at any random timing. + * + * This will need a rework on the async extent lifespan (mark writeback + * and do compression) before deprecating this flag. + */ btrfs_bitmap_nr_locked, btrfs_bitmap_nr_max };