2 files changed, 25 insertions, 2 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 908d3e11ac52..8681cd6f9911 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -77,12 +77,20 @@ void blk_recalc_rq_segments(struct request *rq)
                         continue;
                 }
 new_segment:
+                if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
+                        rq->bio->bi_seg_front_size = seg_size;
+
                 nr_phys_segs++;
                 bvprv = bv;
                 seg_size = bv->bv_len;
                 highprv = high;
         }
 
+        if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
+                rq->bio->bi_seg_front_size = seg_size;
+        if (seg_size > rq->biotail->bi_seg_back_size)
+                rq->biotail->bi_seg_back_size = seg_size;
+
         rq->nr_phys_segments = nr_phys_segs;
 }
 
@@ -106,7 +114,8 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
         if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
                 return 0;
 
-        if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+        if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
+            q->max_segment_size)
                 return 0;
 
         if (!bio_has_data(bio))
@@ -309,6 +318,8 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
                                 struct request *next)
 {
         int total_phys_segments;
+        unsigned int seg_size =
+                req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 
         /*
          * First check if the either of the requests are re-queued
@@ -324,8 +335,13 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
                 return 0;
 
         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
-        if (blk_phys_contig_segment(q, req->biotail, next->bio))
+        if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
+                if (req->nr_phys_segments == 1)
+                        req->bio->bi_seg_front_size = seg_size;
+                if (next->nr_phys_segments == 1)
+                        next->biotail->bi_seg_back_size = seg_size;
                 total_phys_segments--;
+        }
 
         if (total_phys_segments > q->max_phys_segments)
                 return 0;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index ff5b4cf9e2da..dc3cec386a99 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -79,6 +79,13 @@ struct bio {
 
         unsigned int            bi_size;        /* residual I/O count */
 
+        /*
+         * To keep track of the max segment size, we account for the
+         * sizes of the first and last mergeable segments in this bio.
+         */
+        unsigned int            bi_seg_front_size;
+        unsigned int            bi_seg_back_size;
+
         unsigned int            bi_max_vecs;    /* max bvl_vecs we can hold */
 
         unsigned int            bi_comp_cpu;    /* completion CPU */