linux-kernel - Re: [PATCH v3] f2fs: introduce flush

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Message-ID: <7a2534f5-bf20-4d3c-afe7-afcb8f340929@acm.org>
Date: Mon, 11 Aug 2025 06:44:01 -0700
From: Bart Van Assche <bvanassche@....org>
To: Christoph Hellwig <hch@...radead.org>, Chao Yu <chao@...nel.org>
Cc: jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH v3] f2fs: introduce flush_policy sysfs entry

On 8/11/25 3:52 AM, Christoph Hellwig wrote:
> On Thu, Aug 07, 2025 at 11:48:38AM +0800, Chao Yu wrote:
>> This patch introduces a new sysfs entry /sys/fs/f2fs/<disk>/flush_policy
>> in order to tune performance of f2fs data flush flow.
>>
>> For example, checkpoint will use REQ_FUA to persist CP metadata, however,
>> some kind device has bad performance on REQ_FUA command, result in that
>> checkpoint being blocked for long time, w/ this sysfs entry, we can give
>> an option to use REQ_PREFLUSH command instead of REQ_FUA during checkpoint,
>> it can help to mitigate long latency of checkpoint.
> 
> That's and odd place to deal with this.  If that's a real issue it
> should be a block layer tweak to disable FUA, potentially with a quirk
> entry in the driver to disable it rather than having to touch a file
> system sysfs attribute.

Chao, two years ago Christoph already suggested to integrate this
functionality in the UFS driver. From
https://lore.kernel.org/linux-scsi/Y+NCDzvuLJYGwyhC@infradead.org/:
"Please add quirks for the actually affected devices, and do not
block fua for an entire transport."

See also the ufs_fixups[] array in drivers/ufs/core/ufshcd.c.

Bart.