[PATCH 08/15] iomap: refactor iomap_bio_read_folio_range

[Christoph Hellwig <hch@lst.de>]

Split out the logic to allocate a new bio and only keep the fast path
that adds more data to an existing bio in iomap_bio_read_folio_range.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Tested-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/iomap/bio.c | 69 +++++++++++++++++++++++++++-----------------------
 1 file changed, 37 insertions(+), 32 deletions(-)

diff --git a/fs/iomap/bio.c b/fs/iomap/bio.c
index fc045f2e4c45..578b1202e037 100644
--- a/fs/iomap/bio.c
+++ b/fs/iomap/bio.c
@@ -26,45 +26,50 @@ static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
 		submit_bio(bio);
 }
 
-static int iomap_bio_read_folio_range(const struct iomap_iter *iter,
+static void iomap_read_alloc_bio(const struct iomap_iter *iter,
 		struct iomap_read_folio_ctx *ctx, size_t plen)
 {
-	struct folio *folio = ctx->cur_folio;
 	const struct iomap *iomap = &iter->iomap;
-	loff_t pos = iter->pos;
-	size_t poff = offset_in_folio(folio, pos);
-	loff_t length = iomap_length(iter);
-	sector_t sector;
+	unsigned int nr_vecs = DIV_ROUND_UP(iomap_length(iter), PAGE_SIZE);
+	struct folio *folio = ctx->cur_folio;
+	gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
+	gfp_t orig_gfp = gfp;
 	struct bio *bio = ctx->read_ctx;
 
-	sector = iomap_sector(iomap, pos);
-	if (!bio || bio_end_sector(bio) != sector ||
-	    !bio_add_folio(bio, folio, plen, poff)) {
-		gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
-		gfp_t orig_gfp = gfp;
-		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
+	if (bio)
+		submit_bio(bio);
+
+	/* Same as readahead_gfp_mask: */
+	if (ctx->rac)
+		gfp |= __GFP_NORETRY | __GFP_NOWARN;
 
-		if (bio)
-			submit_bio(bio);
+	/*
+	 * If the bio_alloc fails, try it again for a single page to avoid
+	 * having to deal with partial page reads.  This emulates what
+	 * do_mpage_read_folio does.
+	 */
+	bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ, gfp);
+	if (!bio)
+		bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ, orig_gfp);
+	if (ctx->rac)
+		bio->bi_opf |= REQ_RAHEAD;
+	bio->bi_iter.bi_sector = iomap_sector(iomap, iter->pos);
+	bio->bi_end_io = iomap_read_end_io;
+	bio_add_folio_nofail(bio, folio, plen,
+			offset_in_folio(folio, iter->pos));
+	ctx->read_ctx = bio;
+}
+
+static int iomap_bio_read_folio_range(const struct iomap_iter *iter,
+		struct iomap_read_folio_ctx *ctx, size_t plen)
+{
+	struct folio *folio = ctx->cur_folio;
+	struct bio *bio = ctx->read_ctx;
 
-		if (ctx->rac) /* same as readahead_gfp_mask */
-			gfp |= __GFP_NORETRY | __GFP_NOWARN;
-		bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ,
-				     gfp);
-		/*
-		 * If the bio_alloc fails, try it again for a single page to
-		 * avoid having to deal with partial page reads.  This emulates
-		 * what do_mpage_read_folio does.
-		 */
-		if (!bio)
-			bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ, orig_gfp);
-		if (ctx->rac)
-			bio->bi_opf |= REQ_RAHEAD;
-		bio->bi_iter.bi_sector = sector;
-		bio->bi_end_io = iomap_read_end_io;
-		bio_add_folio_nofail(bio, folio, plen, poff);
-		ctx->read_ctx = bio;
-	}
+	if (!bio ||
+	    bio_end_sector(bio) != iomap_sector(&iter->iomap, iter->pos) ||
+	    !bio_add_folio(bio, folio, plen, offset_in_folio(folio, iter->pos)))
+		iomap_read_alloc_bio(iter, ctx, plen);
 	return 0;
 }
 
-- 
2.47.3