linux-kernel - Re: 5.7-rc0: kswapd eats cpu during a disk test?!

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Message-ID: <e3afe444-4541-b420-0888-575cae8aa46d@suse.cz>
Date:   Mon, 1 Jun 2020 10:55:24 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Pavel Machek <pavel@....cz>,
        kernel list <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...l.org>
Cc:     mhocko@...e.cz, "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: 5.7-rc0: kswapd eats cpu during a disk test?!

+CC linux-mm

On 5/31/20 12:34 PM, Pavel Machek wrote:
> Hi!
> 
> This is simple cat /dev/sda > /dev/zero... on thinkpad x60 (x86-32),
> with spinning rust.
> 
>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+  COMMAND
>    1000 root      20   0       0      0      0 R  53.3  0.0  57:34.93  kswapd0
>   27897 root      20   0    6976    580    536 R  44.5  0.0   1:44.53  cat
> 
> It keeps both CPUs busy... and I don't think that's right.

Does an older kernel behave differently here?