linux-kernel - Re: [External] Re: [PATCH] cgroup/cpuset: Add a new isolated mems.policy type.

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Date:   Fri, 9 Sep 2022 10:55:55 +0800
From:   Zhongkun He <hezhongkun.hzk@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     hannes@...xchg.org, roman.gushchin@...ux.dev,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, lizefan.x@...edance.com,
        wuyun.abel@...edance.com
Subject: Re: [External] Re: [PATCH] cgroup/cpuset: Add a new isolated
 mems.policy type.

> On Wed 07-09-22 21:50:24, Zhongkun He wrote:
> [...]
>>> Do you really need to change the policy itself or only the effective
>>> nodemask? Do you need any other policy than bind and preferred?
>>
>> Yes, we need to change the policy, not only his nodemask. we really want
>> policy is interleave, and extend it to weight-interleave.
>> Say something like the following
>> 			node       weight
>>      interleave:		 0-3       1:1:1:1  default one by one
>>      weight-interleave:   0-3       1:2:4:6  alloc pages by weight
>> 					    (User set weight.)
>> In the actual usecase, the remaining resources of each node are different,
>> and the use of interleave cannot maximize the use of resources.
> 
> OK, this seems a separate topic. It would be good to start by proposing
> that new policy in isolation with the semantic description.
> 
>> Back to the previous question.
>>> The question is how to implement that with a sensible semantic.
>>
>> Thanks for your analysis and suggestions.It is really difficult to add
>> policy directly to cgroup for the hierarchical enforcement. It would be a
>> good idea to add pidfd_set_mempolicy.
> 
> Are you going to pursue that path?
>   
>> Also, there is a new idea.
>> We can try to separate the elements of mempolicy and use them independently.
>> Mempolicy has two meanings:
>>      nodes:which nodes to use(nodes,0-3), we can use cpuset's effective_mems
>> directly.
>>      mode:how to use them(bind,prefer,etc). change the mode to a
>> cpuset->flags,such as CS_INTERLEAVE。
>> task_struct->mems_allowed is equal to cpuset->effective_mems,which is
>> hierarchical enforcement。CS_INTERLEAVE can also be updated into tasks，
>> just like other flags(CS_SPREAD_PAGE).
>> When a process needs to allocate memory, it can find the appropriate node to
>> allocate pages according to the flag and mems_allowed.
> 
> I am not sure I see the advantage as the mode and nodes are always
> closely coupled. You cannot really have one wihtout the other.
> 

Hi Michal, thanks for your suggestion and reply.

 > Are you going to pursue that path?

Yes，I'll give it a try as it makes sense to modify the policy dynamically.

Thanks.