linux-kernel - Re: [PATCH v2] proc: add percpu populated pages count to meminfo

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Message-ID: <20180807201028.GA12087@castle.DHCP.thefacebook.com>
Date:   Tue, 7 Aug 2018 13:10:32 -0700
From:   Roman Gushchin <guro@...com>
To:     Dennis Zhou <dennisszhou@...il.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Christoph Lameter <cl@...ux.com>,
        Vlastimil Babka <vbabka@...e.cz>, <kernel-team@...com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] proc: add percpu populated pages count to meminfo

On Tue, Aug 07, 2018 at 11:47:23AM -0700, Dennis Zhou wrote:
> From: "Dennis Zhou (Facebook)" <dennisszhou@...il.com>
> 
> Currently, percpu memory only exposes allocation and utilization
> information via debugfs. This more or less is only really useful for
> understanding the fragmentation and allocation information at a
> per-chunk level with a few global counters. This is also gated behind a
> config. BPF and cgroup, for example, have seen an increase use causing
> increased use of percpu memory. Let's make it easier for someone to
> identify how much memory is being used.
> 
> This patch adds the "Percpu" stat to meminfo to more easily look up how
> much percpu memory is in use. This number includes the cost for all
> allocated backing pages and not just isnight at the a unit, per chunk
> level. Metadata is excluded. I think excluding metadata is fair because
> the backing memory scales with the numbere of cpus and can quickly
> outweigh the metadata. It also makes this calculation light.
> 
> Signed-off-by: Dennis Zhou <dennisszhou@...il.com>

Acked-by: Roman Gushchin <guro@...com>

It's super useful! I've seen hosts in production which have
tens and hundreds on megabytes in per-cpu memory, and with
vmalloc counters being defined to 0, it's really hard
to notice and track down.

Thanks, Dennis!