linux-kernel - Re: [fuse-devel] Horrible mmap write performance (kernel writeback issue?)

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Date:	Tue, 12 Apr 2016 07:09:03 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Ashish Sangwan <ashishsangwan2@...il.com>
Cc:	Jakob Unterwurzacher <jakobunt@...il.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [fuse-devel] Horrible mmap write performance (kernel writeback
 issue?)

Hello,

On Tue, Apr 12, 2016 at 02:54:08PM +0530, Ashish Sangwan wrote:
> On Tue, Apr 12, 2016 at 5:54 AM, Tejun Heo <tj@...nel.org> wrote:
> > Hello,
> >
> > On Mon, Apr 11, 2016 at 10:04:42AM +0200, Jakob Unterwurzacher wrote:
> >> What seems to be happening in the kernel is that the estimated device bandwith
> >> drops to zero. I'm not even sure how this works for FUSE, but that's what I
> >> gathered from some printk debugging.
> >
> > Yeah, writeback bw getting messed up is the most likely cause.  Prolly
> > some silly bug.  I can reproduce the problem.  Looking into it.
> 
> Probably you want to look into:
> https://lkml.org/lkml/2016/3/10/21
> 
> The patch mentioned above solves the issue for me.

Heh, I tracked it down to wb_over_bg_thresh() and fell asleep.  Yeah,
that is the right fix.

Thanks.

-- 
tejun