block: fix bio_will_gap() for first bvec with offset

[mirror_ubuntu-zesty-kernel.git] / include / linux / blkdev.h

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ca8e8fd10789d0fff1aa0b21ede64b72075e094..758ff0e75cce9db129655dad92333794b7da1278 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1620,16 +1620,60 @@ static inline bool bvec_gap_to_prev(struct request_queue *q,
        return __bvec_gap_to_prev(q, bprv, offset);
 }
 
-static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
-                        struct bio *next)
+/*
+ * Check if the two bvecs from two bios can be merged to one segment.
+ * If yes, no need to check gap between the two bios since the 1st bio
+ * and the 1st bvec in the 2nd bio can be handled in one segment.
+ */
+static inline bool bios_segs_mergeable(struct request_queue *q,
+               struct bio *prev, struct bio_vec *prev_last_bv,
+               struct bio_vec *next_first_bv)
+{
+       if (!BIOVEC_PHYS_MERGEABLE(prev_last_bv, next_first_bv))
+               return false;
+       if (!BIOVEC_SEG_BOUNDARY(q, prev_last_bv, next_first_bv))
+               return false;
+       if (prev->bi_seg_back_size + next_first_bv->bv_len >
+                       queue_max_segment_size(q))
+               return false;
+       return true;
+}
+
+static inline bool bio_will_gap(struct request_queue *q,
+                               struct request *prev_rq,
+                               struct bio *prev,
+                               struct bio *next)
 {
        if (bio_has_data(prev) && queue_virt_boundary(q)) {
                struct bio_vec pb, nb;
 
+               /*
+                * don't merge if the 1st bio starts with non-zero
+                * offset, otherwise it is quite difficult to respect
+                * sg gap limit. We work hard to merge a huge number of small
+                * single bios in case of mkfs.
+                */
+               if (prev_rq)
+                       bio_get_first_bvec(prev_rq->bio, &pb);
+               else
+                       bio_get_first_bvec(prev, &pb);
+               if (pb.bv_offset)
+                       return true;
+
+               /*
+                * We don't need to worry about the situation that the
+                * merged segment ends in unaligned virt boundary:
+                *
+                * - if 'pb' ends aligned, the merged segment ends aligned
+                * - if 'pb' ends unaligned, the next bio must include
+                *   one single bvec of 'nb', otherwise the 'nb' can't
+                *   merge with 'pb'
+                */
                bio_get_last_bvec(prev, &pb);
                bio_get_first_bvec(next, &nb);
 
-               return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
+               if (!bios_segs_mergeable(q, prev, &pb, &nb))
+                       return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
        }
 
        return false;
@@ -1637,12 +1681,12 @@ static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
 
 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
 {
-       return bio_will_gap(req->q, req->biotail, bio);
+       return bio_will_gap(req->q, req, req->biotail, bio);
 }
 
 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
 {
-       return bio_will_gap(req->q, bio, req->bio);
+       return bio_will_gap(req->q, NULL, bio, req->bio);
 }
 
 int kblockd_schedule_work(struct work_struct *work);