linux-kernel - Re: [PATCH 02/16] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu

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Date:   Sun, 20 Oct 2019 22:51:10 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Roman Gushchin <guro@...com>
cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 02/16] mm: vmstat: use s32 for vm_node_stat_diff in struct
 per_cpu_nodestat

On Thu, 17 Oct 2019, Roman Gushchin wrote:

> Currently s8 type is used for per-cpu caching of per-node statistics.
> It works fine because the overfill threshold can't exceed 125.
>
> But if some counters are in bytes (and the next commit in the series
> will convert slab counters to bytes), it's not gonna work:
> value in bytes can easily exceed s8 without exceeding the threshold
> converted to bytes. So to avoid overfilling per-cpu caches and breaking
> vmstats correctness, let's use s32 instead.

Actually this is inconsistenct since the other counters are all used to
account for pages. Some of the functions in use for the page counters will
no longer make sense. inc/dec_node_state() etc.