linux-kernel - Re: [PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage

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Message-ID: <YmmRFOXJsjLj4a7T@cmpxchg.org>
Date:   Wed, 27 Apr 2022 14:53:08 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage

On Wed, Apr 27, 2022 at 11:36:54AM -0700, Andrew Morton wrote:
> On Wed, 27 Apr 2022 12:00:15 -0400 Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > Currently it requires poking at debugfs to figure out the size and
> > population of the zswap cache on a host. There are no counters for
> > reads and writes against the cache. As a result, it's difficult to
> > understand zswap behavior on production systems.
> > 
> > Print zswap memory consumption and how many pages are zswapped out in
> > /proc/meminfo. Count zswapouts and zswapins in /proc/vmstat.
> 
> /proc/meminfo is rather prime real estate.  Is this important enough to
> be placed in there, or should it instead be in the more lowly
> /proc/vmstat?

The zswap pool size is capped to 20% of available RAM, and we usually
have a utilization of tens of gigabytes. I think it's fair to say it's
a first class memory consumer when enabled, and actually a huge hole
in /proc/meminfo coverage right now.

> /proc/meminfo is documented in Documentation/filesystems/proc.rst ;)
> 
> That file appears to need a bit of updating for other things.

"The following is from a 16GB PIII, which has highmem enabled."

lmao.

I'll send a general update for that, and a delta fixlet for 4/5.

Thanks!