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

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Message-ID: <alpine.DEB.2.21.1910202243220.593@www.lameter.com>
Date:   Sun, 20 Oct 2019 22:44:10 +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:

> 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.

This quardruples the cache footprint of the counters and likely has some
influence on performance.