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Subject: Re: [RESEND PATCH v5 2/2] bio: add limit_bio_size sysfs
To:     Changheun Lee <nanich.lee@samsung.com>, Johannes.Thumshirn@wdc.com,
        asml.silence@gmail.com, axboe@kernel.dk, damien.lemoal@wdc.com,
        gregkh@linuxfoundation.org, hch@infradead.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        ming.lei@redhat.com, osandov@fb.com, patchwork-bot@kernel.org,
        tj@kernel.org, tom.leiming@gmail.com
Cc:     jisoo2146.oh@samsung.com, junho89.kim@samsung.com,
        mj0123.lee@samsung.com, seunghwan.hyun@samsung.com,
        sookwan7.kim@samsung.com, woosung2.lee@samsung.com,
        yt0928.kim@samsung.com
References: <20210316074401.4594-1-nanich.lee@samsung.com>
 <CGME20210316080106epcas1p3522dda95e9c97fc39b40b008bbf87c04@epcas1p3.samsung.com>
 <20210316074401.4594-2-nanich.lee@samsung.com>
From:   Bart Van Assche <bvanassche@acm.org>
Message-ID: <7c8d9787-f0eb-9ef1-6ebf-f383c27b599a@acm.org>
Date:   Tue, 6 Apr 2021 14:05:27 -0700
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On 3/16/21 12:44 AM, Changheun Lee wrote:
> Add limit_bio_size block sysfs node to limit bio size.
> Queue flag QUEUE_FLAG_LIMIT_BIO_SIZE will be set if limit_bio_size is set.
> And bio max size will be limited by queue max sectors via
> QUEUE_FLAG_LIMIT_BIO_SIZE set.
> 
> Signed-off-by: Changheun Lee <nanich.lee@samsung.com>
> ---
>  Documentation/ABI/testing/sysfs-block | 10 ++++++++++
>  Documentation/block/queue-sysfs.rst   |  7 +++++++
>  block/blk-sysfs.c                     |  3 +++
>  3 files changed, 20 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
> index e34cdeeeb9d4..86a7b15410cf 100644
> --- a/Documentation/ABI/testing/sysfs-block
> +++ b/Documentation/ABI/testing/sysfs-block
> @@ -316,3 +316,13 @@ Description:
>  		does not complete in this time then the block driver timeout
>  		handler is invoked. That timeout handler can decide to retry
>  		the request, to fail it or to start a device recovery strategy.
> +
> +What:		/sys/block/<disk>/queue/limit_bio_size
> +Date:		Feb, 2021
> +Contact:	Changheun Lee <nanich.lee@samsung.com>
> +Description:
> +		(RW) Toggle for set/clear QUEUE_FLAG_LIMIT_BIO_SIZE queue flag.
> +		Queue flag QUEUE_FLAG_LIMIT_BIO_SIZE will be set if limit_bio_size
> +		is set. And bio max size will be limited by queue max sectors.
> +		QUEUE_FLAG_LIMIT_BIO_SIZE will be cleared if limit_bio_size is
> +		cleard. And limit of bio max size will be cleard.
> diff --git a/Documentation/block/queue-sysfs.rst b/Documentation/block/queue-sysfs.rst
> index 2638d3446b79..cd371a821855 100644
> --- a/Documentation/block/queue-sysfs.rst
> +++ b/Documentation/block/queue-sysfs.rst
> @@ -273,4 +273,11 @@ devices are described in the ZBC (Zoned Block Commands) and ZAC
>  do not support zone commands, they will be treated as regular block devices
>  and zoned will report "none".
>  
> +limit_bio_size (RW)
> +-------------------
> +This indicates QUEUE_FLAG_LIMIT_BIO_SIZE queue flag value. And
> +QUEUE_FLAG_LIMIT_BIO_SIZE can be changed via set(1)/clear(0) this node.
> +bio max size will be limited by queue max sectors via set this node. And
> +limit of bio max size will be cleard via clear this node.
> +
>  Jens Axboe <jens.axboe@oracle.com>, February 2009
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index b513f1683af0..840d97f427e6 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -288,6 +288,7 @@ QUEUE_SYSFS_BIT_FNS(nonrot, NONROT, 1);
>  QUEUE_SYSFS_BIT_FNS(random, ADD_RANDOM, 0);
>  QUEUE_SYSFS_BIT_FNS(iostats, IO_STAT, 0);
>  QUEUE_SYSFS_BIT_FNS(stable_writes, STABLE_WRITES, 0);
> +QUEUE_SYSFS_BIT_FNS(limit_bio_size, LIMIT_BIO_SIZE, 0);
>  #undef QUEUE_SYSFS_BIT_FNS
>  
>  static ssize_t queue_zoned_show(struct request_queue *q, char *page)
> @@ -615,6 +616,7 @@ QUEUE_RW_ENTRY(queue_nonrot, "rotational");
>  QUEUE_RW_ENTRY(queue_iostats, "iostats");
>  QUEUE_RW_ENTRY(queue_random, "add_random");
>  QUEUE_RW_ENTRY(queue_stable_writes, "stable_writes");
> +QUEUE_RW_ENTRY(queue_limit_bio_size, "limit_bio_size");
>  
>  static struct attribute *queue_attrs[] = {
>  	&queue_requests_entry.attr,
> @@ -648,6 +650,7 @@ static struct attribute *queue_attrs[] = {
>  	&queue_rq_affinity_entry.attr,
>  	&queue_iostats_entry.attr,
>  	&queue_stable_writes_entry.attr,
> +	&queue_limit_bio_size_entry.attr,
>  	&queue_random_entry.attr,
>  	&queue_poll_entry.attr,
>  	&queue_wc_entry.attr,

Has it been considered to introduce a function to set the BIO size limit
instead of introducing a new sysfs attribute? See also
blk_queue_max_hw_sectors().

Thanks,

Bart.