linux-kernel - Re: [PATCH] mm/page-writeback: Raise wb_thresh to prevent write blocking with strictlimit

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Message-Id: <20241101071713.4085752-1-jimzhao.ai@gmail.com>
Date: Fri,  1 Nov 2024 15:17:13 +0800
From: Jim Zhao <jimzhao.ai@...il.com>
To: akpm@...ux-foundation.org
Cc: jimzhao.ai@...il.com,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	willy@...radead.org
Subject: Re: [PATCH] mm/page-writeback: Raise wb_thresh to prevent write blocking with strictlimit

> On Thu, 24 Oct 2024 15:29:19 +0800 Jim Zhao <jimzhao.ai@...il.com> wrote:
> 
> > > > 2. FUSE with Unstable Network Backends and Occasional Writes
> > > > Not easy to reproduce, but when it occurs in this scenario, 
> > > > it causes the write thread to experience more pauses and longer durations.
> > 
> > > Thanks, but it's still unclear how this impacts our users.  How lenghty
> > > are these pauses?
> > 
> > The length is related to device writeback bandwidth.
> > Under normal bandwidth, each pause may last around 4ms in several times as shown in the trace above(5 times).
> > In extreme cases, fuse with unstable network backends,
> > if pauses occur frequently and bandwidth is low, each pause can exceed 10ms, the total duration of pauses can accumulate to second.
> 
> Thanks.  I'll assume that the userspace impact isn't serious to warrant
> a backport into -stable kernel.
> 
> If you disagree with this, please let me know and send along additional
> changelog text which helps others understand why we think our users
> will significantly benefit from this change.

It’s acceptable not to backport this to earlier kernels. 
After additional testing,  under normal conditions, the impact on userspace is limited, with blocking times generally in the millisecond range.
However, I recommend including this patch in the next kernel version. 
In cases of low writeback bandwidth and high writeback delay, blocking times can significantly increase. 
This patch helps eliminate unnecessary blocks in those scenarios.
Thanks.