block/merge: count bytes instead of sectors

Individual bv_len's may not be a sector size.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20220610195830.3574005-7-kbusch@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 7771dac..db2e03c 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -201,11 +201,11 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
  * @nsegs:    [in,out] Number of segments in the bio being built. Incremented
  *            by the number of segments from @bv that may be appended to that
  *            bio without exceeding @max_segs
- * @sectors:  [in,out] Number of sectors in the bio being built. Incremented
- *            by the number of sectors from @bv that may be appended to that
- *            bio without exceeding @max_sectors
+ * @bytes:    [in,out] Number of bytes in the bio being built. Incremented
+ *            by the number of bytes from @bv that may be appended to that
+ *            bio without exceeding @max_bytes
  * @max_segs: [in] upper bound for *@nsegs
- * @max_sectors: [in] upper bound for *@sectors
+ * @max_bytes: [in] upper bound for *@bytes
  *
  * When splitting a bio, it can happen that a bvec is encountered that is too
  * big to fit in a single segment and hence that it has to be split in the
@@ -216,10 +216,10 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
  */
 static bool bvec_split_segs(const struct request_queue *q,
                            const struct bio_vec *bv, unsigned *nsegs,
-                           unsigned *sectors, unsigned max_segs,
-                           unsigned max_sectors)
+                           unsigned *bytes, unsigned max_segs,
+                           unsigned max_bytes)
 {
-       unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
+       unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
        unsigned len = min(bv->bv_len, max_len);
        unsigned total_len = 0;
        unsigned seg_size = 0;
@@ -237,7 +237,7 @@ static bool bvec_split_segs(const struct request_queue *q,
                        break;
        }
 
-       *sectors += total_len >> 9;
+       *bytes += total_len;
 
        /* tell the caller to split the bvec if it is too big to fit */
        return len > 0 || bv->bv_len > max_len;
@@ -269,8 +269,8 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 {
        struct bio_vec bv, bvprv, *bvprvp = NULL;
        struct bvec_iter iter;
-       unsigned nsegs = 0, sectors = 0;
-       const unsigned max_sectors = get_max_io_size(q, bio);
+       unsigned nsegs = 0, bytes = 0;
+       const unsigned max_bytes = get_max_io_size(q, bio) << 9;
        const unsigned max_segs = queue_max_segments(q);
 
        bio_for_each_bvec(bv, bio, iter) {
@@ -282,12 +282,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
                        goto split;
 
                if (nsegs < max_segs &&
-                   sectors + (bv.bv_len >> 9) <= max_sectors &&
+                   bytes + bv.bv_len <= max_bytes &&
                    bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
                        nsegs++;
-                       sectors += bv.bv_len >> 9;
-               } else if (bvec_split_segs(q, &bv, &nsegs, &sectors, max_segs,
-                                        max_sectors)) {
+                       bytes += bv.bv_len;
+               } else if (bvec_split_segs(q, &bv, &nsegs, &bytes, max_segs,
+                                          max_bytes)) {
                        goto split;
                }
 
@@ -301,12 +301,19 @@ split:
        *segs = nsegs;
 
        /*
+        * Individual bvecs might not be logical block aligned. Round down the
+        * split size so that each bio is properly block size aligned, even if
+        * we do not use the full hardware limits.
+        */
+       bytes = ALIGN_DOWN(bytes, queue_logical_block_size(q));
+
+       /*
         * Bio splitting may cause subtle trouble such as hang when doing sync
         * iopoll in direct IO routine. Given performance gain of iopoll for
         * big IO can be trival, disable iopoll when split needed.
         */
        bio_clear_polled(bio);
-       return bio_split(bio, sectors, GFP_NOIO, bs);
+       return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
 }
 
 /**
@@ -375,7 +382,7 @@ EXPORT_SYMBOL(blk_queue_split);
 unsigned int blk_recalc_rq_segments(struct request *rq)
 {
        unsigned int nr_phys_segs = 0;
-       unsigned int nr_sectors = 0;
+       unsigned int bytes = 0;
        struct req_iterator iter;
        struct bio_vec bv;
 
@@ -398,7 +405,7 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
        }
 
        rq_for_each_bvec(bv, rq, iter)
-               bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
+               bvec_split_segs(rq->q, &bv, &nr_phys_segs, &bytes,
                                UINT_MAX, UINT_MAX);
        return nr_phys_segs;
 }