linux-kernel - Re: [PATCH] loop: change fsync to fdatasync when update dio

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Date:   Fri, 3 Feb 2023 03:12:41 +0900
From:   Huijin Park <bbanghj.park@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Huijin Park <huijin.park@...sung.com>,
        Jens Axboe <axboe@...nel.dk>,
        Chaitanya Kulkarni <kch@...dia.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] loop: change fsync to fdatasync when update dio

On Thu, Jan 26, 2023 at 2:31 PM Christoph Hellwig <hch@....de> wrote:
>
> On Thu, Jan 26, 2023 at 02:16:57PM +0900, Huijin Park wrote:
> > In general, fsync has a larger overhead than fdatasync. And since the
> > dio option is for data, it seems like fdatasync is enough.
> > So this patch changes it to fdatasync which has little load relatively.
>
> The only difference is that fsync also syncs the timestamps.  So this
> change looks correct, but also a bit useless given that buffered to
> direct I/O or back changes aren't exactly a fast path.

Although the difference will be minimal, why I suggested it is because
it can reduce unnecessary metadata i/o (helpful on slow i/o devices),
and using fdatasync looked correct like your opinion.
In some environment cases, loop setup for mount is required when
application is initialized and this change will help.