Re: [PATCH v3] f2fs: introduce flush_policy sysfs entry

[Chao Yu <chao@kernel.org>]

On 8/11/25 21:44, Bart Van Assche wrote:
> 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, thank you for letting me know the history and decision there. I had a
qemu option here to resolve my current issue, thanks.

Thanks,

> 
> Bart.