From: Yu Kuai Date: Mon, 23 Feb 2026 03:58:34 +0000 (+0800) Subject: md/raid5: set chunk_sectors to enable full stripe I/O splitting X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d51e1668fad6d7d34feea5735264929aabb95975;p=thirdparty%2Fkernel%2Flinux.git md/raid5: set chunk_sectors to enable full stripe I/O splitting Set chunk_sectors to the full stripe width (io_opt) so that the block layer splits I/O at full stripe boundaries. This ensures that large writes are aligned to full stripes, avoiding the read-modify-write overhead that occurs with partial stripe writes in RAID-5/6. When chunk_sectors is set, the block layer's bio splitting logic in get_max_io_size() uses blk_boundary_sectors_left() to limit I/O size to the boundary. This naturally aligns split bios to full stripe boundaries, enabling more efficient full stripe writes. Test results with 24-disk RAID5 (chunk_size=64k): dd if=/dev/zero of=/dev/md0 bs=10M oflag=direct Before: 461 MB/s After: 520 MB/s (+12.8%) Link: https://lore.kernel.org/linux-raid/20260223035834.3132498-1-yukuai@fnnas.com Suggested-by: Christoph Hellwig Reviewed-by: Paul Menzel Reviewed-by: Christoph Hellwig Signed-off-by: Yu Kuai --- diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index ba9d6d05b089..2ec6dd6ddd93 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -7780,6 +7780,7 @@ static int raid5_set_limits(struct mddev *mddev) lim.logical_block_size = mddev->logical_block_size; lim.io_min = mddev->chunk_sectors << 9; lim.io_opt = lim.io_min * (conf->raid_disks - conf->max_degraded); + lim.chunk_sectors = lim.io_opt >> 9; lim.features |= BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE; lim.discard_granularity = stripe; lim.max_write_zeroes_sectors = 0;