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

Johannes Weiner
2022-04-27T18:53:08Z

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@cmpxchg.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!