linux-kernel - Re: [PATCH 1/2] f2fs: add sysfs nodes to get discard information

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Message-ID: <ee60f940-c1a6-e41d-a163-bf277290c231@kernel.org>
Date:   Thu, 19 Aug 2021 12:49:36 +0800
From:   Chao Yu <chao@...nel.org>
To:     李扬韬 <frank.li@...o.com>
Cc:     jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] f2fs: add sysfs nodes to get discard information

On 2021/8/16 14:13, 李扬韬 wrote:
>>>>> I've added new sysfs nodes to show discard stat since mount, which
>>>>> will help us analyze whether the performance problem is related to
>>>>> discard.
>>>>>
>>>>> issued_discard  - Shows the number of issued discard
>>>>> queued_discard  - Shows the number of cached discard cmd count
>>>>> discard_cmd_cnt - Shows the number of cached discard cmd count
>>>>> undiscard_blks  - Shows the number of undiscard blocks
>>>>
>>>> We have exported them in debugfs, can you use that?
>>>>
>>>> Thanks,
>>>
>>> But now Android is forbidden to open debugfs, and in fact we have not
>>> opened this configuration for a long time.
>>
>> Weren't them be used for debug purpose? can you please explain more about
>> your use case?
> 
> During long-term aging test or normal use, sometimes there will be performance
> degradation problems. It may be caused by storage, or it may be caused by the
> filesystem. For example, the filesystem accumulates a large number of undiscard
>   blocks. Although there is some remaining space, the androidbench test will
> show performance degradation. Therefore, it is necessary to export information
> related to discard so that we can confirm this situation.

I have a solution for your case, however finally, we haven't used such discard
policy by default due to the policy needs to be designed more tunable for
devices with different characters.

See more details in below patches:

https://lkml.org/lkml/2018/8/10/219
https://lkml.org/lkml/2018/8/10/220

Thanks,

> 
> Thx,
> 
>