[PATCH 6/9] iomap: Convert read_count to byte count

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Instead of counting bio segments, count the number of bytes submitted.
This insulates us from the block layer's definition of what a 'same page'
is, which is not necessarily clear once THPs are involved.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/iomap/buffered-io.c | 29 ++++++++++-------------------
 1 file changed, 10 insertions(+), 19 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 844e95cacea8..c9b44f86d166 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -161,13 +161,6 @@ iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
 		SetPageUptodate(page);
 }
 
-static void
-iomap_read_finish(struct iomap_page *iop, struct page *page)
-{
-	if (!iop || atomic_dec_and_test(&iop->read_count))
-		unlock_page(page);
-}
-
 static void
 iomap_read_page_end_io(struct bio_vec *bvec, int error)
 {
@@ -181,7 +174,8 @@ iomap_read_page_end_io(struct bio_vec *bvec, int error)
 		iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
 	}
 
-	iomap_read_finish(iop, page);
+	if (!iop || atomic_sub_and_test(bvec->bv_len, &iop->read_count))
+		unlock_page(page);
 }
 
 static void
@@ -269,20 +263,17 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	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;
-	}
-
 	/*
-	 * If we start a new segment we need to increase the read count, and we
-	 * need to do so before submitting any previous full bio to make sure
-	 * that we don't prematurely unlock the page.
+	 * We need to increase the read count before submitting any
+	 * previous bio to make sure that we don't prematurely unlock
+	 * the page.
 	 */
 	if (iop)
-		atomic_inc(&iop->read_count);
+		atomic_add(plen, &iop->read_count);
+
+	if (is_contig &&
+	    __bio_try_merge_page(ctx->bio, page, plen, poff, &same_page))
+		goto done;
 
 	if (!ctx->bio || !is_contig || bio_full(ctx->bio, plen)) {
 		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
-- 
2.28.0