From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Subject: Re: [PATCH v2 6/6] zswap: memcg accounting
Date: Wed, 11 May 2022 15:06:56 -0400
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To: Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny-IBi9RG/b67k@public.gmane.org>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>, Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>, Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Seth Jennings <sjenning-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Dan Streetman <ddstreet-EkmVulN54Sk@public.gmane.org>, Minchan Kim <minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org

On Wed, May 11, 2022 at 07:32:18PM +0200, Michal Koutn=FD wrote:
> Hello.
>=20
> On Tue, May 10, 2022 at 11:28:47AM -0400, Johannes Weiner <hannes-druUgvl=
0LCNAfugRpC6u6w@public.gmane.org> wrote:
> > +void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size)
> > +{
> > +	struct mem_cgroup *memcg;
> > +
> > +	VM_WARN_ON_ONCE(!(current->flags & PF_MEMALLOC));
> > +
> > +	/* PF_MEMALLOC context, charging must succeed */
> > +	if (obj_cgroup_charge(objcg, GFP_KERNEL, size))
> > +		VM_WARN_ON_ONCE(1);
>=20
> IIUC, the objcg is derived from the compressed page, i.e. same memcg
> (reparenting neglected for now). This memcg's memory.current is then
> charged with the compressed object size.

Correct. After which the uncompressed page is reclaimed and uncharged.
So the zswapout process will reduce the charge bottom line.

> Do I get it right that memory.zswap.current is a subset of memory.current?
>
> (And that zswap is limited both by memory.max and memory.zswap.max?)

Yes. Zswap is a memory consumer, and we want the compressed part of a
workload's memory to show up in the total memory footprint.

memory.zswap.* are there to configure zswap policy, within the
boundaries of available memory - it's by definition a subset.