Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 7 Aug 2019 09:59:27 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Suren Baghdasaryan <surenb@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Artem S. Tashkinov" <aros@gmx.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>
Subject: Re: Let's talk about the elephant in the room - the Linux kernel's
 inability to gracefully handle low memory pressure
Message-ID: <20190807075927.GO11812@dhcp22.suse.cz>
References: <d9802b6a-949b-b327-c4a6-3dbca485ec20@gmx.com>
 <ce102f29-3adc-d0fd-41ee-e32c1bcd7e8d@suse.cz>
 <20190805193148.GB4128@cmpxchg.org>
 <CAJuCfpHhR+9ybt9ENzxMbdVUd_8rJN+zFbDm+5CeE2Desu82Gg@mail.gmail.com>
 <398f31f3-0353-da0c-fc54-643687bb4774@suse.cz>
 <20190806142728.GA12107@cmpxchg.org>
 <20190806143608.GE11812@dhcp22.suse.cz>
 <CAJuCfpFmOzj-gU1NwoQFmS_pbDKKd2XN=CS1vUV4gKhYCJOUtw@mail.gmail.com>
 <20190806220150.GA22516@cmpxchg.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190806220150.GA22516@cmpxchg.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue 06-08-19 18:01:50, Johannes Weiner wrote:
> On Tue, Aug 06, 2019 at 09:27:05AM -0700, Suren Baghdasaryan wrote:
[...]
> > > > I'm not sure 10s is the perfect value here, but I do think the kernel
> > > > should try to get out of such a state, where interacting with the
> > > > system is impossible, within a reasonable amount of time.
> > > >
> > > > It could be a little too short for non-interactive number-crunching
> > > > systems...
> > >
> > > Would it be possible to have a module with tunning knobs as parameters
> > > and hook into the PSI infrastructure? People can play with the setting
> > > to their need, we wouldn't really have think about the user visible API
> > > for the tuning and this could be easily adopted as an opt-in mechanism
> > > without a risk of regressions.
> 
> It's relatively easy to trigger a livelock that disables the entire
> system for good, as a regular user. It's a little weird to make the
> bug fix for that an opt-in with an extensive configuration interface.

Yes, I definitely do agree that this is a bug fix more than a
feature. The thing is that we do not know what the proper default is for
a wide variety of workloads so some way of configurability is needed
(level and period).  If making this a module would require a lot of
additional code then we need a kernel command line parameter at least.

A module would have a nice advantage that you can change your
configuration without rebooting. The same can be achieved by a sysfs on
the other hand.
-- 
Michal Hocko
SUSE Labs