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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 9 Aug 2018 09:14:28 +0200
Message-ID: <CAJfpegtOqbhwKBpaGdWwcBG5sBrbjtLFzpFsqsB8_VbT7=vE9w@mail.gmail.com>
Subject: Re: FUSE: write operations trigger balance_dirty_pages when using
 writeback cache
To:     =?UTF-8?B?5YiY56GV54S2?= <liushuoran@jd.com>
Cc:     "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Thu, Aug 9, 2018 at 5:37 AM, =E5=88=98=E7=A1=95=E7=84=B6 <liushuoran@jd.=
com> wrote:
> Dear Miklos,
>
> Recently I've been testing FUSE and libfuse example passthrough_ll with w=
riteback cache on, and found out that the performance drops significantly c=
ompared to that in local filesystem. As I can see from trace, balance_dirty=
_pages is triggered very frequently even if there not enough pages that sha=
ll be sent to libfuse. I'm not sure if this is a known fact or the FUSE wri=
teback feature requires some specific configurations. Trace log is attached=
.
>
> dd-19067 [001] .... 195295.568097: balance_dirty_pages: bdi 0:42: limit=
=3D3180390 setpoint=3D2782421 dirty=3D5 bdi_setpoint=3D0 bdi_dirty=3D32 dir=
ty_ratelimit=3D32 task_ratelimit=3D0 dirtied=3D32 dirtied_pause=3D32 paused=
=3D0 pause=3D33 period=3D33 think=3D0 cgroup_ino=3D1
> dd-19067 [001] .... 195295.602029: balance_dirty_pages: bdi 0:42: limit=
=3D3180390 setpoint=3D2782421 dirty=3D5 bdi_setpoint=3D0 bdi_dirty=3D33 dir=
ty_ratelimit=3D32 task_ratelimit=3D0 dirtied=3D1 dirtied_pause=3D0 paused=
=3D0 pause=3D34 period=3D34 think=3D1 cgroup_ino=3D1
> dd-19067 [001] .... 195295.637026: balance_dirty_pages: bdi 0:42: limit=
=3D3180390 setpoint=3D2782421 dirty=3D5 bdi_setpoint=3D0 bdi_dirty=3D34 dir=
ty_ratelimit=3D32 task_ratelimit=3D0 dirtied=3D1 dirtied_pause=3D0 paused=
=3D0 pause=3D35 period=3D35 think=3D1 cgroup_ino=3D1
>
> BTW, I'm using Linux kernel 4.17.12 and libfuse 3.2.5. Look forward to he=
aring from you. Thanks in advance.

Try

   echo 20 > /sys/devices/virtual/bdi/0:`stat -c %d /mnt/fuse/`/max_ratio

where you replace /mnt/fuse with your mountpoint.

Thanks,
Miklos