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[BLOCK] bio: check for same page merge possibilities in __bio_add_page() 

For filesystems with a blocksize < page size, we can merge same page
calls into the bio_vec at the end of the bio. This saves segments
on systems with a page size > the "normal" 4kb fs block size.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@suse.de>
This commit is contained in:
Jens Axboe 2006-01-06 09:43:28 +01:00
parent 88ee5ef157
commit 80cfd548ee
1 changed files with 24 additions and 2 deletions
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26
fs/bio.c
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@ -325,10 +325,31 @@ static int __bio_add_page(request_queue_t *q, struct bio *bio, struct page
if (unlikely(bio_flagged(bio, BIO_CLONED)))
return 0;
if (bio->bi_vcnt >= bio->bi_max_vecs)
if (((bio->bi_size + len) >> 9) > max_sectors)
return 0;
if (((bio->bi_size + len) >> 9) > max_sectors)
/*
* For filesystems with a blocksize smaller than the pagesize
* we will often be called with the same page as last time and
* a consecutive offset. Optimize this special case.
*/
if (bio->bi_vcnt > 0) {
struct bio_vec *prev = &bio->bi_io_vec[bio->bi_vcnt - 1];
if (page == prev->bv_page &&
offset == prev->bv_offset + prev->bv_len) {
prev->bv_len += len;
if (q->merge_bvec_fn &&
q->merge_bvec_fn(q, bio, prev) < len) {
prev->bv_len -= len;
return 0;
}
goto done;
}
}
if (bio->bi_vcnt >= bio->bi_max_vecs)
return 0;
/*
@ -382,6 +403,7 @@ static int __bio_add_page(request_queue_t *q, struct bio *bio, struct page
bio->bi_vcnt++;
bio->bi_phys_segments++;
bio->bi_hw_segments++;
done:
bio->bi_size += len;
return len;
}