Revert "block: blk-merge: try to make front segments in full size"

This reverts commit a2d37968d784363842f87820a21e106741d28004.

If max segment size isn't 512-aligned, this patch won't work well.

Also once multipage bvec is enabled, adjacent bvecs won't be physically
contiguous if page is added via bio_add_page(), so we don't need this
kind of complicated logic.

Reported-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 5 insertions, 49 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 446f63e076aa..8452fc7164cc 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -109,7 +109,6 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
         bool do_split = true;
         struct bio *new = NULL;
         const unsigned max_sectors = get_max_io_size(q, bio);
-        unsigned advance = 0;
 
         bio_for_each_segment(bv, bio, iter) {
                 /*
@@ -133,32 +132,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
                 }
 
                 if (bvprvp && blk_queue_cluster(q)) {
+                        if (seg_size + bv.bv_len > queue_max_segment_size(q))
+                                goto new_segment;
                         if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
                                 goto new_segment;
                         if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
                                 goto new_segment;
-                        if (seg_size + bv.bv_len > queue_max_segment_size(q)) {
-                                /*
-                                 * One assumption is that initial value of
-                                 * @seg_size(equals to bv.bv_len) won't be
-                                 * bigger than max segment size, but this
-                                 * becomes false after multipage bvecs.
-                                 */
-                                advance = queue_max_segment_size(q) - seg_size;
-
-                                if (advance > 0) {
-                                        seg_size += advance;
-                                        sectors += advance >> 9;
-                                        bv.bv_len -= advance;
-                                        bv.bv_offset += advance;
-                                }
-
-                                /*
-                                 * Still need to put remainder of current
-                                 * bvec into a new segment.
-                                 */
-                                goto new_segment;
-                        }
 
                         seg_size += bv.bv_len;
                         bvprv = bv;
@@ -180,12 +159,6 @@ new_segment:
                 seg_size = bv.bv_len;
                 sectors += bv.bv_len >> 9;
 
-                /* restore the bvec for iterator */
-                if (advance) {
-                        bv.bv_len += advance;
-                        bv.bv_offset -= advance;
-                        advance = 0;
-                }
         }
 
         do_split = false;
@@ -386,29 +359,16 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 {
 
         int nbytes = bvec->bv_len;
-        unsigned advance = 0;
 
         if (*sg && *cluster) {
+                if ((*sg)->length + nbytes > queue_max_segment_size(q))
+                        goto new_segment;
+
                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
                         goto new_segment;
                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
                         goto new_segment;
 
-                /*
-                 * try best to merge part of the bvec into previous
-                 * segment and follow same policy with
-                 * blk_bio_segment_split()
-                 */
-                if ((*sg)->length + nbytes > queue_max_segment_size(q)) {
-                        advance = queue_max_segment_size(q) - (*sg)->length;
-                        if (advance) {
-                                (*sg)->length += advance;
-                                bvec->bv_offset += advance;
-                                bvec->bv_len -= advance;
-                        }
-                        goto new_segment;
-                }
-
                 (*sg)->length += nbytes;
         } else {
 new_segment:
@@ -431,10 +391,6 @@ new_segment:
 
                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
                 (*nsegs)++;
-
-                /* for making iterator happy */
-                bvec->bv_offset -= advance;
-                bvec->bv_len += advance;
         }
         *bvprv = *bvec;
 }