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>

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 446f63e..8452fc7 100644 (file)
--- 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;
 }