From: Shakeel Butt <shakeelb@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Yang Shi <shy828301@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>, Cgroups <cgroups@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: memcg: add swapcache stat for memcg v2
Date: Wed, 6 Jan 2021 08:42:39 -0800 [thread overview]
Message-ID: <CALvZod6Lv3gWmWRPP7jAaw4YCQPyPXcxqXTO3Vp6YVZ6AcEH4w@mail.gmail.com> (raw)
In-Reply-To: <20210106145349.GN13207@dhcp22.suse.cz>
On Wed, Jan 6, 2021 at 6:53 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Thu 31-12-20 18:39:55, Shakeel Butt wrote:
> > This patch adds swapcache stat for the cgroup v2. The swapcache
> > represents the memory that is accounted against both the memory and the
> > swap limit of the cgroup. The main motivation behind exposing the
> > swapcache stat is for enabling users to gracefully migrate from cgroup
> > v1's memsw counter to cgroup v2's memory and swap counters.
> >
> > Cgroup v1's memsw limit allows users to limit the memory+swap usage of a
> > workload but without control on the exact proportion of memory and swap.
> > Cgroup v2 provides separate limits for memory and swap which enables
> > more control on the exact usage of memory and swap individually for the
> > workload.
> >
> > With some little subtleties, the v1's memsw limit can be switched with
> > the sum of the v2's memory and swap limits. However the alternative for
> > memsw usage is not yet available in cgroup v2. Exposing per-cgroup
> > swapcache stat enables that alternative. Adding the memory usage and
> > swap usage and subtracting the swapcache will approximate the memsw
> > usage. This will help in the transparent migration of the workloads
> > depending on memsw usage and limit to v2' memory and swap counters.
>
> Could you expand a bit more on why memsw usage is important even in
> cgroup v2 land? How are you going to use the approximated value?
>
Two main benefits. First, it hides the underlying system's swap setup
from the applications. Applications with multiple instances running in
a datacenter with heterogeneous systems (some have swap and some
don't) will keep seeing a consistent view of their usage.
Second, most of the applications (at least in our prod) are not really
interested in two separate memory and swap usage metrics. A single
usage metric is more simple to use and reason about for these
applications.
next prev parent reply other threads:[~2021-01-06 16:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-01 2:39 [PATCH] mm: memcg: add swapcache stat for memcg v2 Shakeel Butt
2021-01-06 14:53 ` Michal Hocko
2021-01-06 16:42 ` Shakeel Butt [this message]
2021-01-08 13:24 ` Michal Hocko
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