On Mon, Aug 17, 2020 at 08:52:06PM +0100, Matthew Wilcox (Oracle) wrote:
> If we pass in an offset which is larger than PAGE_SIZE, then
> page_is_mergeable() thinks it's not mergeable with the previous bio_vec,
> leading to a large number of bio_vecs being used. Use a slightly more
> obvious test that the two pages are compatible with each other.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Fixes: 52d52d1c98a9 ("block: only allow contiguous page structs in a bio_vec")
>
> ---
> block/bio.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index c63ba04bd629..a9931f23d933 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -740,8 +740,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
> struct page *page, unsigned int len, unsigned int off,
> bool *same_page)
> {
> - phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
> - bv->bv_offset + bv->bv_len - 1;
> + size_t bv_end = bv->bv_offset + bv->bv_len;
> + phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) + bv_end - 1;
> phys_addr_t page_addr = page_to_phys(page);
>
> if (vec_end_addr + 1 != page_addr + off)
> @@ -750,9 +750,9 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
> return false;
>
> *same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
> - if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
> - return false;
> - return true;
> + if (*same_page)
> + return true;
> + return (bv->bv_page + bv_end / PAGE_SIZE) == (page + off / PAGE_SIZE);
Looks this way is more straightforward, meantime can cover compound
pages:
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
