linux-kernel - Re: [PATCH] block/psi: make PSI annotations of submit

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Message-ID: <YjnO3p6vvAjeMCFC@cmpxchg.org>
Date:   Tue, 22 Mar 2022 09:27:58 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     CGEL <cgel.zte@...il.com>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
        Yang Yang <yang.yang29@....com.cn>,
        Ran Xiaokai <ran.xiaokai@....com.cn>
Subject: Re: [PATCH] block/psi: make PSI annotations of submit_bio only work
 for file pages

On Tue, Mar 22, 2022 at 02:47:42AM +0000, CGEL wrote:
> On Mon, Mar 21, 2022 at 10:33:20AM -0400, Johannes Weiner wrote:
> > On Wed, Mar 16, 2022 at 06:39:28AM +0000, cgel.zte@...il.com wrote:
> > > From: Yang Yang <yang.yang29@....com.cn>
> > > 
> > > psi tracks the time spent on submitting the IO of refaulting file pages
> > > and anonymous pages[1]. But after we tracks refaulting anonymous pages
> > > in swap_readpage[2][3], there is no need to track refaulting anonymous
> > > pages in submit_bio.
> > > 
> > > So this patch can reduce redundant calling of psi_memstall_enter. And
> > > make it easier to track refaulting file pages and anonymous pages
> > > separately.
> > 
> > I don't think this is an improvement.
> > 
> > psi_memstall_enter() will check current->in_memstall once, detect the
> > nested call, and bail. Your patch checks PageSwapBacked for every page
> > being added. It's more branches for less robust code.
> 
> We are also working for a new patch to classify different reasons cause
> psi_memstall_enter(): reclaim, thrashing, compact, etc. This will help
> user to tuning sysctl, for example, if user see high compact delay, he
> may try do adjust THP sysctl to reduce the compact delay.
> 
> To support that, we should distinguish what's the reason cause psi in
> submit_io(), this patch does the job.

Please submit these patches together then. On its own, this patch
isn't desirable.