Re: [PATCH 1/4] memcg, mm: introduce lowlimit reclaim

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, May 02, 2014 at 06:00:56PM -0400, Johannes Weiner wrote:
> On Fri, May 02, 2014 at 06:49:30PM +0200, Michal Hocko wrote:
> > On Fri 02-05-14 11:58:05, Johannes Weiner wrote:
> > > This is not even guarantees anymore, but rather another reclaim
> > > prioritization scheme with best-effort semantics.  That went over
> > > horribly with soft limits, and I don't want to repeat this.
> > > 
> > > Overcommitting on guarantees makes no sense, and you even agree you
> > > are not interested in it.  We also agree that we can always add a knob
> > > later on to change semantics when an actual usecase presents itself,
> > > so why not start with the clear and simple semantics, and the simpler
> > > implementation?
> > 
> > So you are really preferring an OOM instead? That was the original
> > implementation posted at the end of last year and some people
> > had concerns about it. This is the primary reason I came up with a
> > weaker version which fallbacks rather than OOM.
> 
> I'll dig through the archives on this then, thanks.

The most recent discussion on this I could find was between you and
Greg, where the final outcome was (excerpt):

---

From: Greg Thelen <gthelen@google.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: linux-mm@kvack.org,  Johannes Weiner <hannes@cmpxchg.org>,  Andrew Morton <akpm@linux-foundation.org>,  KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,  LKML <linux-kernel@vger.kernel.org>,  Ying Han <yinghan@google.com>,  Hugh Dickins <hughd@google.com>,  Michel Lespinasse <walken@google.com>,  KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,  Tejun Heo <tj@kernel.org>
Subject: Re: [RFC 0/4] memcg: Low-limit reclaim
References: <1386771355-21805-1-git-send-email-mhocko@suse.cz>
	<xr93sis6obb5.fsf@gthelen.mtv.corp.google.com>
	<20140130123044.GB13509@dhcp22.suse.cz>
	<xr931tzphu50.fsf@gthelen.mtv.corp.google.com>
	<20140203144341.GI2495@dhcp22.suse.cz>
Date: Mon, 03 Feb 2014 17:33:13 -0800
Message-ID: <xr93zjm7br1i.fsf@gthelen.mtv.corp.google.com>
List-ID: <linux-mm.kvack.org>

On Mon, Feb 03 2014, Michal Hocko wrote:

> On Thu 30-01-14 16:28:27, Greg Thelen wrote:
>> But this soft_limit,priority extension can be added later.
>
> Yes, I would like to have the strong semantic first and then deal with a
> weaker form. Either by a new limit or a flag.

Sounds good.

---

So I think everybody involved in the discussions so far are preferring
a hard guarantee, and then later, if needed, to either add a knob to
make it a soft guarantee or to actually implement a usable soft limit.

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