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authorIlya Dryomov <idryomov@gmail.com>2015-06-12 19:19:02 +0300
committerIlya Dryomov <idryomov@gmail.com>2015-06-25 18:30:49 +0300
commitd3834fefcfe5610702379d78596337875df2db5b (patch)
treea2bd9206d624107073692213dfd5cd82a6a213d2
parentfdd4e15838e59c394a1ec4963b57c22c12608685 (diff)
downloadlinux-d3834fefcfe5610702379d78596337875df2db5b.tar.xz
rbd: bump queue_max_segments
The default queue_limits::max_segments value (BLK_MAX_SEGMENTS = 128) unnecessarily limits bio sizes to 512k (assuming 4k pages). rbd, being a virtual block device, doesn't have any restrictions on the number of physical segments, so bump max_segments to max_hw_sectors, in theory allowing a sector per segment (although the only case this matters that I can think of is some readv/writev style thing). In practice this is going to give us 1M bios - the number of segments in a bio is limited in bio_get_nr_vecs() by BIO_MAX_PAGES = 256. Note that this doesn't result in any improvement on a typical direct sequential test. This is because on a box with a not too badly fragmented memory the default BLK_MAX_SEGMENTS is enough to see nice rbd object size sized requests. The only difference is the size of bios being merged - 512k vs 1M for something like $ dd if=/dev/zero of=/dev/rbd0 oflag=direct bs=$RBD_OBJ_SIZE $ dd if=/dev/rbd0 iflag=direct of=/dev/null bs=$RBD_OBJ_SIZE Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Alex Elder <elder@linaro.org>
-rw-r--r--drivers/block/rbd.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 89fe8a4bc02e..bc88fbcb9715 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3791,6 +3791,7 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
/* set io sizes to object size */
segment_size = rbd_obj_bytes(&rbd_dev->header);
blk_queue_max_hw_sectors(q, segment_size / SECTOR_SIZE);
+ blk_queue_max_segments(q, segment_size / SECTOR_SIZE);
blk_queue_max_segment_size(q, segment_size);
blk_queue_io_min(q, segment_size);
blk_queue_io_opt(q, segment_size);