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

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

Hi,

在 2025/08/17 23:26, colyli@xxxxxxxxxx 写道:
> From: Coly Li <colyli@xxxxxxxxxx>
>
> 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.
It's better refering to the thread:

https://lore.kernel.org/all/ywsfp3lqnijgig6yrlv2ztxram6ohf5z4yfeebswjkvp2dzisd@f5ikoyo3sfq5/

That scsi and mdraid have different definition of io_opt.

> For md raid5, it is necessary to keep a proper io_opt size for better
> I/O thoughput.
>
> Signed-off-by: Coly Li <colyli@xxxxxxxxxx>
> ---
>   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);

And I think raid0/raid1/raid10 should all set this flag as well.

Thanks,
Kuai

> 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;