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: <20190807140130.7418e783654a9c53e6b6cd1b@linux-foundation.org>
Date:   Wed, 7 Aug 2019 14:01:30 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        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 Wed, 7 Aug 2019 16:51:38 -0400 Johannes Weiner <hannes@...xchg.org> wrote:

> However, eb414681d5a0 ("psi: pressure stall information for CPU,
> memory, and IO") introduced a memory pressure metric that quantifies
> the share of wallclock time in which userspace waits on reclaim,
> refaults, swapins. By using absolute time, it encodes all the above
> mentioned variables of hardware capacity and workload behavior. When
> memory pressure is 40%, it means that 40% of the time the workload is
> stalled on memory, period. This is the actual measure for the lack of
> forward progress that users can experience. It's also something they
> expect the kernel to manage and remedy if it becomes non-existent.
> 
> To accomplish this, this patch implements a thrashing cutoff for the
> OOM killer. If the kernel determines a sustained high level of memory
> pressure, and thus a lack of forward progress in userspace, it will
> trigger the OOM killer to reduce memory contention.
> 
> Per default, the OOM killer will engage after 15 seconds of at least
> 80% memory pressure. These values are tunable via sysctls
> vm.thrashing_oom_period and vm.thrashing_oom_level.

Could be implemented in userspace?
</troll>