linux-kernel - Re: [PATCH 2/5] mm: correct calculation of cgroup wb's bg_thresh in wb_over_bg

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Date: Thu, 8 Feb 2024 09:32:09 -1000
From: Tejun Heo <tj@...nel.org>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: willy@...radead.org, akpm@...ux-foundation.org,
	hcochran@...nelspring.com, mszeredi@...hat.com, axboe@...nel.dk,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] mm: correct calculation of cgroup wb's bg_thresh in
 wb_over_bg_thresh

Hello, Kemeng.

On Thu, Feb 08, 2024 at 05:26:10PM +0800, Kemeng Shi wrote:
> Hi Tejun, sorry for the delay as I found there is a issue that keep triggering
> writeback even the dirty page is under dirty background threshold. The issue
> make it difficult to observe the expected improvment from this patch. I try to
> fix it in [1] and test this patch based on the fix patches.
> Run test as following:

Ah, that looks promising and thanks a lot for looking into this. It's great
to have someone actually poring over the code and behavior. Understanding
the wb and cgroup wb behaviors have always been challenging because the only
thing we have is the tracepoints and it's really tedious and difficult to
build an overall understanding from the trace outputs. Can I persuade you
into writing a drgn monitoring script similar to e.g.
tools/workqueues/wq_monitor.py? I think there's a pretty good chance the
visibility can be improved substantially.

Thanks.

-- 
tejun