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

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Message-ID: <4d7beb50-f778-507a-4c3c-f6de92f8cfb9@kernel.org>
Date:   Mon, 10 Sep 2018 20:02:05 -0600
From:   Shuah Khan <shuah@...nel.org>
To:     Michal Hocko <mhocko@...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,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH] arm64: add NUMA emulation support

Hi Michal,

On 09/10/2018 07:48 AM, Michal Hocko wrote:
> On Fri 07-09-18 16:30:59, Shuah Khan wrote:
>> On 09/07/2018 02:34 AM, Michal Hocko wrote:
>>> On Thu 06-09-18 15:53:34, Shuah Khan wrote:
[....]
>>
>> In addition to isolation, being able to reserve a block instead is one of the
>> issues I am looking to address. Unfortunately memory cgroups won't address that
>> issue.
> 
> Could you be more specific why you need reservations other than
> isolation.
> 

Taking automotive as a specific example, there are two classes of applications:
1. critical applications that must run
2. Infotainment and misc. user-space.

In this case, being able to reserve a block of memory for critical applications
will ensure the memory is available for them. If a critical application has to
restart and/or when an on-demand critical application starts, it might not be able
to allocate memory if it is not reserved.

When a flat system has multiple memory blocks, with NUMA emulation in conjunction with
cpusets, one or more block can be reserved for critical applications configuring a set
of cpus and one of more memory nodes for them.

Memory cgroups will not support such reservation. Hope this helps explain the use-case
I am trying to address with this patch.

thanks,
-- Shuah