Re: [PATCH] arm64: add NUMA emulation support

[Shuah Khan <shuah@kernel.org>]

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