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

[Roman Gushchin <guro@fb.com>]

On Tue, Aug 07, 2018 at 11:47:23AM -0700, Dennis Zhou wrote:
> From: "Dennis Zhou (Facebook)" <dennisszhou@gmail.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@gmail.com>

Acked-by: Roman Gushchin <guro@fb.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!