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

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Message-ID: <YjiMsGoXoDU+FwsS@cmpxchg.org>
Date:   Mon, 21 Mar 2022 10:33:20 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     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 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.