Re: [PATCH v3 1/4] memcg: introduce per-memcg reclaim interface

From: Yosry Ahmed <yosryahmed@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: "Johannes Weiner" <hannes@cmpxchg.org>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Roman Gushchin" <roman.gushchin@linux.dev>,
	"David Rientjes" <rientjes@google.com>,
	"Tejun Heo" <tj@kernel.org>,
	"Dan Schatzberg" <schatzberg.dan@gmail.com>,
	"Zefan Li" <lizefan.x@bytedance.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Shuah Khan" <shuah@kernel.org>, "Yu Zhao" <yuzhao@google.com>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Wei Xu" <weixugc@google.com>, "Greg Thelen" <gthelen@google.com>,
	"Chen Wandun" <chenwandun@huawei.com>,
	"Vaibhav Jain" <vaibhav@linux.ibm.com>,
	"Michal Koutný" <mkoutny@suse.com>,
	"Tim Chen" <tim.c.chen@linux.intel.com>,
	cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 1/4] memcg: introduce per-memcg reclaim interface
Date: Thu, 14 Apr 2022 10:25:29 -0700	[thread overview]
Message-ID: <CAJD7tkYJj2O-zaux9BZxJxG+JBjPrwRYKXPAAAh7i9GVE53VGQ@mail.gmail.com> (raw)
In-Reply-To: <CAJD7tkbFjbGJ7CnNogpGq5enh_uhP8T5c0U+ku9PfwMoVLf2gg@mail.gmail.com>

On Fri, Apr 8, 2022 at 1:08 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> On Fri, Apr 8, 2022 at 7:55 AM Dan Schatzberg <schatzberg.dan@gmail.com> wrote:
> >
> > On Fri, Apr 08, 2022 at 04:11:05PM +0200, Michal Hocko wrote:
> > > Regarding "max" as a possible input. I am not really sure to be honest.
> > > I can imagine that it could be legit to simply reclaim all the charges
> > > (e.g. before removing the memcg) which should be achieveable by
> > > reclaiming the reported consumption. Or what exactly should be the
> > > semantic?
> >
> > Yeah, it just allows you to avoid reading memory.current to just
> > reclaim everything if you can specify "max" - you're still protected
> > by nretries to eventually bail out. Mostly, though I just feel like
> > supporting "max" makes memory.reclaim semetric with a lot of the
> > cgroup memory control files which tend to support "max".
>
> One possible approach here is to have force_empty behavior when we
> write "max" to memory.reclaim. From Google's perspective we don't have
> a preference, but it seems to me like logical behavior. We can do this
> either by directly calling mem_cgroup_force_empty() or just draining
> stock and lrus in memory_reclaim().
>
> This actually brings up another interesting point. Do you think we
> should drain lrus if try_to_free_mem_cgroup_pages() fails to reclaim
> the request amount? We can do this after the first call or before the
> last one. It could introduce more evictable pages for
> try_to_free_mem_cgroup_pages() to free.

Hey Michal, any thoughts on this? I am looking for feedback on this
before I send out v4.