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 23:09:48 +0800 [thread overview]
Message-ID: <5bcc52dc-ca8f-bbdd-69ef-4b6312e7994a@suse.de> (raw)
In-Reply-To: <20200921140010.GA14672@lst.de>
On 2020/9/21 22:00, Christoph Hellwig wrote:
> On Mon, Sep 21, 2020 at 05:54:59PM +0800, Coly Li wrote:
>> 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 ?
>
> Well, if the optimal I/O size is wrong, the read ahead size also is
> wrong. Can we just drop the setting?
>
I feel this is something should be fixed. Indeed I overlooked it until
you point out the issue now.
The optimal request size and read ahead pages hint are necessary, but
current initialization is simple. A better way might be dynamically
setting them depends on the cache mode and some special configuration.
By your inspiration, I want to ACK your original patch although it
doesn't work fine for all condition. Then we may know these two settings
(ra_pages and queue_io_opt) should be improved for more situations. At
lease for most part of the situations they provide proper hints.
How do you think of the above idea ?
Coly Li
WARNING: multiple messages have this Message-ID (diff)
From: Coly Li <colyli@suse.de>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-raid@vger.kernel.org, Hans de Goede <hdegoede@redhat.com>,
Justin Sanders <justin@coraid.com>,
Minchan Kim <minchan@kernel.org>,
Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-block@vger.kernel.org, Song Liu <song@kernel.org>,
dm-devel@redhat.com, linux-mtd@lists.infradead.org,
Richard Weinberger <richard@nod.at>,
linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, drbd-dev@lists.linbit.com
Subject: Re: [PATCH 03/13] bcache: inherit the optimal I/O size
Date: Mon, 21 Sep 2020 23:09:48 +0800 [thread overview]
Message-ID: <5bcc52dc-ca8f-bbdd-69ef-4b6312e7994a@suse.de> (raw)
In-Reply-To: <20200921140010.GA14672@lst.de>
On 2020/9/21 22:00, Christoph Hellwig wrote:
> On Mon, Sep 21, 2020 at 05:54:59PM +0800, Coly Li wrote:
>> 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 ?
>
> Well, if the optimal I/O size is wrong, the read ahead size also is
> wrong. Can we just drop the setting?
>
I feel this is something should be fixed. Indeed I overlooked it until
you point out the issue now.
The optimal request size and read ahead pages hint are necessary, but
current initialization is simple. A better way might be dynamically
setting them depends on the cache mode and some special configuration.
By your inspiration, I want to ACK your original patch although it
doesn't work fine for all condition. Then we may know these two settings
(ra_pages and queue_io_opt) should be improved for more situations. At
lease for most part of the situations they provide proper hints.
How do you think of the above idea ?
Coly Li
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Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2020-09-21 15:10 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 8:07 bdi cleanups v6 Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-21 8:07 ` 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 ` 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 ` Christoph Hellwig
2020-09-21 8:07 ` [PATCH 03/13] bcache: inherit the optimal I/O size Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-21 9:54 ` Coly Li
2020-09-21 9:54 ` Coly Li
2020-09-21 14:00 ` Christoph Hellwig
2020-09-21 14:00 ` Christoph Hellwig
2020-09-21 14:00 ` Christoph Hellwig
2020-09-21 15:09 ` Coly Li [this message]
2020-09-21 15:09 ` Coly Li
2020-09-21 18:18 ` Christoph Hellwig
2020-09-21 18:18 ` Christoph Hellwig
2020-09-22 8:44 ` Jan Kara
2020-09-22 8:44 ` Jan Kara
2020-09-22 8:44 ` Jan Kara
2020-09-22 9:39 ` Coly Li
2020-09-22 9:39 ` Coly Li
2020-09-21 8:07 ` [PATCH 04/13] aoe: set an " Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-22 8:45 ` Jan Kara
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
2020-09-21 8:07 ` Christoph Hellwig
2020-09-22 8:49 ` Jan Kara
2020-09-22 8:49 ` Jan Kara
2020-09-22 8:49 ` Jan Kara
2020-09-23 15:16 ` Christoph Hellwig
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 ` Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-21 8:07 ` [PATCH 07/13] block: lift setting the readahead size into the block layer Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-22 9:13 ` Jan Kara
2020-09-22 9:13 ` Jan Kara
2020-09-22 9:51 ` Coly Li
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 ` Christoph Hellwig
2020-09-21 8:07 ` [PATCH 09/13] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-21 8:07 ` [PATCH 10/13] mm: use SWP_SYNCHRONOUS_IO more intelligently Christoph Hellwig
2020-09-21 8:07 ` 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 ` Christoph Hellwig
2020-09-21 8:07 ` [PATCH 12/13] bdi: invert BDI_CAP_NO_ACCT_WB Christoph Hellwig
2020-09-21 8:07 ` Christoph Hellwig
2020-09-21 8:07 ` [PATCH 13/13] bdi: replace BDI_CAP_NO_{WRITEBACK,ACCT_DIRTY} with a single flag Christoph Hellwig
2020-09-21 8:07 ` [PATCH 13/13] bdi: replace BDI_CAP_NO_{WRITEBACK, ACCT_DIRTY} " 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 6:51 ` Christoph Hellwig
2020-09-24 15:49 ` Martin K. Petersen
2020-09-24 15:49 ` Martin K. Petersen
2020-09-24 15:49 ` Martin K. Petersen
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