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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Date:   Tue, 6 Aug 2019 22:43:25 +0100
From:   James Courtier-Dutton <james.dutton@...il.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Artem S. Tashkinov" <aros@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Michal Hocko <mhocko@...nel.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, 6 Aug 2019 at 02:09, Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> 80% of the last 10 seconds spent in full stall would definitely be a
> problem. If the system was already low on memory (which it probably
> is, or we would not be reclaiming so hard and registering such a big
> stall) then oom-killer would probably kill something before 8 seconds
> are passed.

There are other things to consider also.
I can reproduce these types of symptoms and memory pressure is 100%
NOT the cause. (top showing 4GB of a 16GB system in use)
The cause as I see it is disk pressure and the lack of multiple queues
for disk IO requests.
For example, one process can hog 100% of the disk, without other
applications even being able to write just one sector.
We need a way for the linux kernel to better multiplex access to the
disk. Adding QOS, allowing interactive processes to interrupt long
background disk IO tasks.
If we could balance disk access across each active process, the user,
on their desktop, would think the system was more responsive.

Kind Regards

James