linux-kernel - Re: [PATCH] mm/vmscan.c: only adjust related kswapd cpu affinity when online cpu

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Message-Id: <20200213213207.34b2aa0e0c2c92a09b700e96@linux-foundation.org>
Date:   Thu, 13 Feb 2020 21:32:07 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmscan.c: only adjust related kswapd cpu affinity
 when online cpu

On Tue, 28 Jan 2020 08:39:42 +0800 Wei Yang <richardw.yang@...ux.intel.com> wrote:

> >Is there ever a situation where the cpu to be onlined would have appeared 
> >in the cpumask of another node and so a different kswapd's cpumask would 
> >now include an off-node cpu?
> 
> No, I don't think so.
> 
> Per my understanding, kswapd_cpu_online() will be invoked when a cpu is
> onlined. And the particular cpu belongs to a particular numa node. So it is
> not necessary to iterate on every nodes.
> 
> And current code use cpumask_and_any() to do the check. If my understanding is
> correct, the check would return true if this node has any online cpu. This is
> likely to be true.
> 
> This is why I want to make the logic clear.

Please resend with a changelog which explains the above?