block: return from __bio_try_merge_page if merging occured in the same page

We currently have an input same_page parameter to __bio_try_merge_page
to prohibit merging in the same page.  The rationale for that is that
some callers need to account for every page added to a bio.  Instead of
letting these callers call twice into the merge code to account for the
new vs existing page cases, just turn the paramter into an output one that
returns if a merge in the same page occured and let them act accordingly.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -636,7 +636,7 @@ EXPORT_SYMBOL(bio_clone_fast);
 
 static inline bool page_is_mergeable(const struct bio_vec *bv,
 		struct page *page, unsigned int len, unsigned int off,
-		bool same_page)
+		bool *same_page)
 {
 	phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
 		bv->bv_offset + bv->bv_len - 1;
@@ -647,15 +647,9 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
 	if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
 		return false;
 
-	if ((vec_end_addr & PAGE_MASK) != page_addr) {
-		if (same_page)
+	*same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
+	if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
 		return false;
-		if (pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
-			return false;
-	}
-
-	WARN_ON_ONCE(same_page && (len + off) > PAGE_SIZE);
-
 	return true;
 }
 
@@ -701,6 +695,7 @@ static int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
 		bool put_same_page)
 {
 	struct bio_vec *bvec;
+	bool same_page = false;
 
 	/*
 	 * cloned bio must not modify vec list
@@ -729,7 +724,7 @@ static int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
 		if (bvec_gap_to_prev(q, bvec, offset))
 			return 0;
 
-		if (page_is_mergeable(bvec, page, len, offset, false) &&
+		if (page_is_mergeable(bvec, page, len, offset, &same_page) &&
 		    can_add_page_to_seg(q, bvec, page, len, offset)) {
 			bvec->bv_len += len;
 			goto done;
@@ -767,8 +762,7 @@ EXPORT_SYMBOL(bio_add_pc_page);
  * @page: start page to add
  * @len: length of the data to add
  * @off: offset of the data relative to @page
- * @same_page: if %true only merge if the new data is in the same physical
- *		page as the last segment of the bio.
+ * @same_page: return if the segment has been merged inside the same page
  *
  * 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
@@ -779,7 +773,7 @@ EXPORT_SYMBOL(bio_add_pc_page);
  * 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, bool same_page)
+		unsigned int len, unsigned int off, bool *same_page)
 {
 	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
 		return false;
@@ -837,7 +831,9 @@ 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_page(bio, page, len, offset, false)) {
+	bool same_page = false;
+
+	if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
 		if (bio_full(bio))
 			return 0;
 		__bio_add_page(bio, page, len, offset);

fs/iomap.c

@@ -287,7 +287,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	struct iomap_readpage_ctx *ctx = data;
 	struct page *page = ctx->cur_page;
 	struct iomap_page *iop = iomap_page_create(inode, page);
-	bool is_contig = false;
+	bool same_page = false, is_contig = false;
 	loff_t orig_pos = pos;
 	unsigned poff, plen;
 	sector_t sector;
@@ -315,10 +315,14 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	 * Try to merge into a previous segment if we can.
 	 */
 	sector = iomap_sector(iomap, pos);
-	if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
-		if (__bio_try_merge_page(ctx->bio, page, plen, poff, true))
-			goto done;
+	if (ctx->bio && bio_end_sector(ctx->bio) == sector)
 		is_contig = true;
+
+	if (is_contig &&
+	    __bio_try_merge_page(ctx->bio, page, plen, poff, &same_page)) {
+		if (!same_page && iop)
+			atomic_inc(&iop->read_count);
+		goto done;
 	}
 
 	/*

fs/xfs/xfs_aops.c

@@ -758,6 +758,7 @@ xfs_add_to_ioend(
 	struct block_device	*bdev = xfs_find_bdev_for_inode(inode);
 	unsigned		len = i_blocksize(inode);
 	unsigned		poff = offset & (PAGE_SIZE - 1);
+	bool			merged, same_page = false;
 	sector_t		sector;
 
 	sector = xfs_fsb_to_db(ip, wpc->imap.br_startblock) +
@@ -774,9 +775,13 @@ xfs_add_to_ioend(
 				wpc->imap.br_state, offset, bdev, sector);
 	}
 
-	if (!__bio_try_merge_page(wpc->ioend->io_bio, page, len, poff, true)) {
-		if (iop)
+	merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
+			&same_page);
+
+	if (iop && !same_page)
 		atomic_inc(&iop->write_count);
+
+	if (!merged) {
 		if (bio_full(wpc->ioend->io_bio))
 			xfs_chain_bio(wpc->ioend, wbc, bdev, sector);
 		bio_add_page(wpc->ioend->io_bio, page, len, poff);

include/linux/bio.h

@@ -423,7 +423,7 @@ 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, bool same_page);
+		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);