linux-kernel - Re: [PATCH] arm64: add NUMA emulation support

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Message-ID: <20180905064252.GW14951@dhcp22.suse.cz>
Date:   Wed, 5 Sep 2018 08:42:52 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shuah Khan <shuah@...nel.org>
Cc:     Will Deacon <will.deacon@....com>, catalin.marinas@....com,
        sudeep.holla@....com, ganapatrao.kulkarni@...ium.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: add NUMA emulation support

On Tue 04-09-18 15:59:34, Shuah Khan wrote:
[...]
> This will support the following workload requirements:
> 
> - reserving one or more NUMA memory nodes for class of critical tasks that require
>   guaranteed memory availability.
> - isolate memory blocks with a guaranteed exclusive access.

How do you enforce kernel doesn't allocate from those reserved nodes?
They will be in a fallback zonelists so once the memory gets used on all
other ones then the kernel happily spills over to your reserved node.

> NUMA emulation to split the flat machine into "x" number of nodes, combined with
> cpuset cgroup with the following example configuration will make it possible to
> support the above workloads on non-NUMA platforms.
> 
> numa=fake=4
> 
> cpuset.mems=2
> cpuset.cpus=2
> cpuset.mem_exclusive=1 (enabling exclusive use of the memory nodes by a CPU set)
> cpuset.mem_hardwall=1  (separate the memory nodes that are allocated to different cgroups)

This will only enforce userspace to follow and I strongly suspect that
tasks in the root cgroup will be allowed to allocate as well.
-- 
Michal Hocko
SUSE Labs