linux-kernel - Re: [PATCH v2 09/11] mm/vmstat: use cmpxchg loop in cpu_vm_stats

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Message-ID: <ZAES9hPHJGGgCBfc@x1n>
Date:   Thu, 2 Mar 2023 16:19:50 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 09/11] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold

On Thu, Mar 02, 2023 at 10:55:09AM -0300, Marcelo Tosatti wrote:
> >   (2) If someone can modify the dead cpu's vm_stat_diff,
> 
> The only context that can modify the cpu's vm_stat_diff are:
> 
> 1) The CPU itself (increases the counter).
> 2) cpu_vm_stats_fold (from vmstat_shepherd kernel thread), from 
> x -> 0 only.

I think I didn't continue reading so I didn't see cpu_vm_stats_fold() will
be reused when commenting, sorry.

Now with a reworked (and SMP-safe) cpu_vm_stats_fold() and vmstats, I'm
wondering the possibility of merging it with refresh_cpu_vm_stats() since
they really look similar.

IIUC the new refresh_cpu_vm_stats() logically doesn't need the small
preempt disabled sections, not anymore, if with a cpu_id passed over to
cpu_vm_stats_fold(), which seems to be even a good side effect. But not
sure I missed something.

-- 
Peter Xu