linux-kernel - Re: Let's talk about the elephant in the room - the Linux kernel's inability to gracefully handle low memory pressure

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Message-ID: <20190807075927.GO11812@dhcp22.suse.cz>
Date:   Wed, 7 Aug 2019 09:59:27 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Artem S. Tashkinov" <aros@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: Let's talk about the elephant in the room - the Linux kernel's
 inability to gracefully handle low memory pressure

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