block: only allow contiguous page structs in a bio_vec
We currently have to call nth_page when iterating over pages inside a
bio_vec. Jens complained a while ago that this is fairly expensive.
To mitigate this we can check that that the actual page structures
are contiguous when adding them to the bio, and just do check pointer
arithmetics later on.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/bio.c b/block/bio.c
index d3490aeb..8adc2a2 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -659,8 +659,13 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
return false;
if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
return false;
- if (same_page && (vec_end_addr & PAGE_MASK) != page_addr)
- return false;
+
+ if ((vec_end_addr & PAGE_MASK) != page_addr) {
+ if (same_page)
+ return false;
+ if (pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
+ return false;
+ }
return true;
}
