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

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Message-ID: <YxmXeC7te2HAi4dX@dhcp22.suse.cz>
Date:   Thu, 8 Sep 2022 09:19:20 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Zhongkun He <hezhongkun.hzk@...edance.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.

-- 
Michal Hocko
SUSE Labs