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From: Coly Li <colyli@suse.de>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Song Liu <song@kernel.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Richard Weinberger <richard@nod.at>,
	Minchan Kim <minchan@kernel.org>,
	Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
	Justin Sanders <justin@coraid.com>,
	linux-mtd@lists.infradead.org, dm-devel@redhat.com,
	linux-block@vger.kernel.org, linux-bcache@vger.kernel.org,
	linux-kernel@vger.kernel.org, drbd-dev@lists.linbit.com,
	linux-raid@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, cgroups@vger.kernel.org
Subject: Re: [PATCH 03/13] bcache: inherit the optimal I/O size
Date: Mon, 21 Sep 2020 17:54:59 +0800	[thread overview]
Message-ID: <b547a1b6-ab03-0520-012d-86d112c83d92@suse.de> (raw)
In-Reply-To: <20200921080734.452759-4-hch@lst.de>

On 2020/9/21 16:07, Christoph Hellwig wrote:
> Inherit the optimal I/O size setting just like the readahead window,
> as any reason to do larger I/O does not apply to just readahead.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/md/bcache/super.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 1bbdc410ee3c51..48113005ed86ad 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1430,6 +1430,8 @@ static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
>  	dc->disk.disk->queue->backing_dev_info->ra_pages =
>  		max(dc->disk.disk->queue->backing_dev_info->ra_pages,
>  		    q->backing_dev_info->ra_pages);
> +	blk_queue_io_opt(dc->disk.disk->queue,
> +		max(queue_io_opt(dc->disk.disk->queue), queue_io_opt(q)));
>  

Hi Christoph,

I am not sure whether virtual bcache device's optimal request size can
be simply set like this.

Most of time inherit backing device's optimal request size is fine, but
there are two exceptions,
- Read request hits on cache device
- User sets sequential_cuttoff as 0, all writing may go into cache
device firstly.
For the above two conditions, all I/Os goes into cache device, using
optimal request size of backing device might be improper.

Just a guess, is it OK to set the optimal request size of the virtual
bcache device as the least common multiple of cache device's and backing
device's optimal request sizes ?


[snipped]

Thanks.

Coly Li


  reply	other threads:[~2020-09-21  9:55 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21  8:07 bdi cleanups v6 Christoph Hellwig
2020-09-21  8:07 ` [PATCH 01/13] fs: remove the unused SB_I_MULTIROOT flag Christoph Hellwig
2020-09-21  8:07 ` [PATCH 02/13] drbd: remove dead code in device_to_statistics Christoph Hellwig
2020-09-21  8:07 ` [PATCH 03/13] bcache: inherit the optimal I/O size Christoph Hellwig
2020-09-21  9:54   ` Coly Li [this message]
2020-09-21 14:00     ` Christoph Hellwig
2020-09-21 15:09       ` Coly Li
2020-09-21 18:18         ` Christoph Hellwig
2020-09-22  8:44   ` Jan Kara
2020-09-22  9:39   ` Coly Li
2020-09-21  8:07 ` [PATCH 04/13] aoe: set an " Christoph Hellwig
2020-09-22  8:45   ` Jan Kara
2020-09-21  8:07 ` [PATCH 05/13] bdi: initialize ->ra_pages and ->io_pages in bdi_init Christoph Hellwig
2020-09-22  8:49   ` Jan Kara
2020-09-23 15:16     ` Christoph Hellwig
2020-09-21  8:07 ` [PATCH 06/13] md: update the optimal I/O size on reshape Christoph Hellwig
2020-09-21  8:07 ` [PATCH 07/13] block: lift setting the readahead size into the block layer Christoph Hellwig
2020-09-22  9:13   ` Jan Kara
2020-09-22  9:51   ` Coly Li
2020-09-21  8:07 ` [PATCH 08/13] bdi: remove BDI_CAP_CGROUP_WRITEBACK Christoph Hellwig
2020-09-21  8:07 ` [PATCH 09/13] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-09-21  8:07 ` [PATCH 10/13] mm: use SWP_SYNCHRONOUS_IO more intelligently Christoph Hellwig
2020-09-21  8:07 ` [PATCH 11/13] bdi: replace BDI_CAP_STABLE_WRITES with a queue and a sb flag Christoph Hellwig
2020-09-21  8:07 ` [PATCH 12/13] bdi: invert BDI_CAP_NO_ACCT_WB Christoph Hellwig
2020-09-21  8:07 ` [PATCH 13/13] bdi: replace BDI_CAP_NO_{WRITEBACK,ACCT_DIRTY} with a single flag Christoph Hellwig
2020-09-24  6:51 bdi cleanups v7 Christoph Hellwig
2020-09-24  6:51 ` [PATCH 03/13] bcache: inherit the optimal I/O size Christoph Hellwig
2020-09-24 15:49   ` Martin K. Petersen

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