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

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Date:   Tue, 22 Mar 2022 03:44:28 +0000
From:   CGEL <cgel.zte@...il.com>
To:     Johannes Weiner <hannes@...xchg.org>
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 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.

And PageSwapBacked checking is after unlikely(PageWorkingset(page), so I think
the impact is little.