[PATCH 1/2] block: ignore underlying non-stack devices io_opt

[colyli@kernel.org]

From: Coly Li <colyli@kernel.org>

This patch adds a new BLK_FLAG_STACK_IO_OPT for stack block device. If a
stack block device like md raid5 declares its io_opt when don't want
blk_stack_limits() to change it with io_opt of underlying non-stack
block devices, BLK_FLAG_STACK_IO_OPT can be set on limits.flags. Then in
blk_stack_limits(), lcm_not_zero(t->io_opt, b->io_opt) will be avoided.

For md raid5, it is necessary to keep a proper io_opt size for better
I/O thoughput.

Signed-off-by: Coly Li <colyli@kernel.org>
---
 block/blk-settings.c   | 6 +++++-
 drivers/md/raid5.c     | 1 +
 include/linux/blkdev.h | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 07874e9b609f..46ee538b2be9 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -782,6 +782,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 		t->features &= ~BLK_FEAT_POLL;
 
 	t->flags |= (b->flags & BLK_FLAG_MISALIGNED);
+	t->flags |= (b->flags & BLK_FLAG_STACK_IO_OPT);
 
 	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
 	t->max_user_sectors = min_not_zero(t->max_user_sectors,
@@ -839,7 +840,10 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 				     b->physical_block_size);
 
 	t->io_min = max(t->io_min, b->io_min);
-	t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
+	if (!t->io_opt || !(t->flags & BLK_FLAG_STACK_IO_OPT) ||
+	    (b->flags & BLK_FLAG_STACK_IO_OPT))
+		t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
+
 	t->dma_alignment = max(t->dma_alignment, b->dma_alignment);
 
 	/* Set non-power-of-2 compatible chunk_sectors boundary */
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 023649fe2476..989acd8abd98 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7730,6 +7730,7 @@ static int raid5_set_limits(struct mddev *mddev)
 	lim.io_min = mddev->chunk_sectors << 9;
 	lim.io_opt = lim.io_min * (conf->raid_disks - conf->max_degraded);
 	lim.features |= BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE;
+	lim.flags |= BLK_FLAG_STACK_IO_OPT;
 	lim.discard_granularity = stripe;
 	lim.max_write_zeroes_sectors = 0;
 	mddev_stack_rdev_limits(mddev, &lim, 0);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 95886b404b16..a22c7cea9836 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -366,6 +366,9 @@ typedef unsigned int __bitwise blk_flags_t;
 /* passthrough command IO accounting */
 #define BLK_FLAG_IOSTATS_PASSTHROUGH	((__force blk_flags_t)(1u << 2))
 
+/* ignore underlying non-stack devices io_opt */
+#define BLK_FLAG_STACK_IO_OPT		((__force blk_flags_t)(1u << 3))
+
 struct queue_limits {
 	blk_features_t		features;
 	blk_flags_t		flags;
-- 
2.47.2