Re: [PATCH V11 15/19] block: enable multipage bvecs

Christoph Hellwig
2018-11-21T14:55:15Z

On Wed, Nov 21, 2018 at 11:23:23AM +0800, Ming Lei wrote:
> if (bio->bi_vcnt > 0) {
> - struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
> + struct bio_vec bv;
> + struct bio_vec *seg = &bio->bi_io_vec[bio->bi_vcnt - 1];
>
> - if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
> - bv->bv_len += len;
> + bvec_last_segment(seg, &bv);
> +
> + if (page == bv.bv_page && off == bv.bv_offset + bv.bv_len) {

I think this we can simplify the try to merge into bio case a bit,
and also document it better with something like this:

diff --git a/block/bio.c b/block/bio.c
index 854676edc438..cc913281a723 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -822,54 +822,40 @@ EXPORT_SYMBOL(bio_add_pc_page);
* @page: page to add
* @len: length of the data to add
* @off: offset of the data in @page
+ * @same_page: if %true only merge if the new data is in the same physical
+ * page as the last segment of the bio.
*
- * Try to add the data at @page + @off to the last page of @bio. This is a
+ * Try to add the data at @page + @off to the last bvec of @bio. This is a
* a useful optimisation for file systems with a block size smaller than the
* page size.
*
* Return %true on success or %false on failure.
*/
bool __bio_try_merge_page(struct bio *bio, struct page *page,
- unsigned int len, unsigned int off)
+ unsigned int len, unsigned int off, bool same_page)
{
if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
return false;

if (bio->bi_vcnt > 0) {
- struct bio_vec bv;
- struct bio_vec *seg = &bio->bi_io_vec[bio->bi_vcnt - 1];
-
- bvec_last_segment(seg, &bv);
-
- if (page == bv.bv_page && off == bv.bv_offset + bv.bv_len) {
- seg->bv_len += len;
- bio->bi_iter.bi_size += len;
- return true;
- }
+ struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
+ phys_addr_t vec_addr = page_to_phys(bv->bv_page);
+ phys_addr_t page_addr = page_to_phys(page);
+
+ if (vec_addr + bv->bv_offset + bv->bv_len != page_addr + off)
+ return false;
+ if (same_page &&
+ (vec_addr & PAGE_SIZE) != (page_addr & PAGE_SIZE))
+ return false;
+
+ bv->bv_len += len;
+ bio->bi_iter.bi_size += len;
+ return true;
}
return false;
}
EXPORT_SYMBOL_GPL(__bio_try_merge_page);

-static bool bio_try_merge_segment(struct bio *bio, struct page *page,
- unsigned int len, unsigned int off)
-{
- if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
- return false;
-
- if (bio->bi_vcnt > 0) {
- struct bio_vec *seg = &bio->bi_io_vec[bio->bi_vcnt - 1];
-
- if (page_to_phys(seg->bv_page) + seg->bv_offset + seg->bv_len ==
- page_to_phys(page) + off) {
- seg->bv_len += len;
- bio->bi_iter.bi_size += len;
- return true;
- }
- }
- return false;
-}
-
/**
* __bio_add_page - add page to a bio in a new segment
* @bio: destination bio
@@ -910,7 +896,7 @@ EXPORT_SYMBOL_GPL(__bio_add_page);
int bio_add_page(struct bio *bio, struct page *page,
unsigned int len, unsigned int offset)
{
- if (!bio_try_merge_segment(bio, page, len, offset)) {
+ if (!__bio_try_merge_page(bio, page, len, offset, false)) {
if (bio_full(bio))
return 0;
__bio_add_page(bio, page, len, offset);
diff --git a/fs/iomap.c b/fs/iomap.c
index ccc2ba115f4d..d918acb9bfc9 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -313,7 +313,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
*/
sector = iomap_sector(iomap, pos);
if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
- if (__bio_try_merge_page(ctx->bio, page, plen, poff))
+ if (__bio_try_merge_page(ctx->bio, page, plen, poff, true))
goto done;
is_contig = true;
}
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 5c2190216614..b9fd44168f61 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -616,7 +616,7 @@ xfs_add_to_ioend(
bdev, sector);
}

- if (!__bio_try_merge_page(wpc->ioend->io_bio, page, len, poff)) {
+ if (!__bio_try_merge_page(wpc->ioend->io_bio, page, len, poff, true)) {
if (iop)
atomic_inc(&iop->write_count);
if (bio_full(wpc->ioend->io_bio))
diff --git a/include/linux/bio.h b/include/linux/bio.h
index e5b975fa0558..f08e6940c1ab 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -442,7 +442,7 @@ extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
unsigned int, unsigned int);
bool __bio_try_merge_page(struct bio *bio, struct page *page,
- unsigned int len, unsigned int off);
+ unsigned int len, unsigned int off, bool same_page);
void __bio_add_page(struct bio *bio, struct page *page,
unsigned int len, unsigned int off);
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);