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block: remove the same_page output argument to bvec_try_merge_page

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bvec_try_merge_page currently returns if the added page fragment is
within the same page as the last page in the last current bio_vec.

This information is used by __bio_iov_iter_get_pages so that we always
have a single folio pin per page even when the page is split over
multiple __bio_iov_iter_get_pages calls.

Threading this through the entire lowlevel add page to bio logic is
annoying and inefficient and leads to less code sharing than otherwise
possible.  Instead add code to __bio_iov_iter_get_pages that checks if
the bio_vecs did not change and thus a merge into the last segment must
have happened, and if there is an offset into the page for the currently
added fragment, because if yes we must have already had a previous
fragment of the same page in the last bio_vec.  While this is still a bit
ugly, it keeps the logic in the one place that needs it and allows for
more code sharing.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250512042354.514329-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig
2025-05-12 06:23:54 +02:00
committed by Jens Axboe
parent d1ba22ab2b
commit 77fd359b6d
3 changed files with 25 additions and 37 deletions
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3
block/blk.h
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@@ -103,8 +103,7 @@ struct bio_vec *bvec_alloc(mempool_t *pool, unsigned short *nr_vecs,
void bvec_free(mempool_t *pool, struct bio_vec *bv, unsigned short nr_vecs);
bool bvec_try_merge_hw_page(struct request_queue *q, struct bio_vec *bv,
struct page *page, unsigned len, unsigned offset,
bool *same_page);
struct page *page, unsigned len, unsigned offset);
static inline bool biovec_phys_mergeable(struct request_queue *q,
struct bio_vec *vec1, struct bio_vec *vec2)