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iomap: add comments for ifs_clear/set_range_dirty()

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The range alignment strategy differs between ifs_clear_range_dirty() and
ifs_set_range_dirty(). The former rounds inwards to clear only
fully-covered blocks, while the latter rounds outwards to mark any
partially-touched block as dirty. Add comments to document this
asymmetry in block range calculation.

Suggested-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20260714082325.325163-6-yi.zhang@huaweicloud.com
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Zhang Yi 2026-07-14 16:23:25 +08:00 committed by Christian Brauner
parent 9c7d8f7c89
commit 09b53b0787
1 changed files with 14 additions and 0 deletions
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14
fs/iomap/buffered-io.c
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@ -174,6 +174,13 @@ static unsigned iomap_find_dirty_range(struct folio *folio, u64 *range_start,
return range_end - *range_start;
}
/*
* Clear the per-block dirty bits for the range [@off, @off + @len) within a
* folio. The range is rounded inwards so that only blocks fully covered by
* the range are cleared. This is required for operations like folio
* invalidation, where we must ensure a block is fully clean before discarding
* it.
*/
static void ifs_clear_range_dirty(struct folio *folio,
struct iomap_folio_state *ifs, size_t off, size_t len)
{
@ -201,6 +208,13 @@ static void iomap_clear_range_dirty(struct folio *folio, size_t off, size_t len)
ifs_clear_range_dirty(folio, ifs, off, len);
}
/*
* Set the per-block dirty bits for the range [@off, @off + @len) within a
* folio. The range is rounded outwards so that any block partially touched
* by the range is marked dirty. This ensures blocks containing even a
* single dirty byte will be included in subsequent writeback, preventing
* data loss when partial blocks are written.
*/
static void ifs_set_range_dirty(struct folio *folio,
struct iomap_folio_state *ifs, size_t off, size_t len)
{