linux-kernel - Re: [PATCH] mm/vmscan: respect cpuset policy during page demotion

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Message-ID: <87wn8gcr5s.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Mon, 31 Oct 2022 16:51:11 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Feng Tang <feng.tang@...el.com>,
        Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Waiman Long <longman@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Chen, Tim C" <tim.c.chen@...el.com>,
        "Yin, Fengwei" <fengwei.yin@...el.com>
Subject: Re: [PATCH] mm/vmscan: respect cpuset policy during page demotion

Michal Hocko <mhocko@...e.com> writes:

> On Fri 28-10-22 07:22:27, Huang, Ying wrote:
>> Michal Hocko <mhocko@...e.com> writes:
>> 
>> > On Thu 27-10-22 17:31:35, Huang, Ying wrote:
> [...]
>> >> I think that it's possible for different processes have different
>> >> requirements.
>> >> 
>> >> - Some processes don't care about where the memory is placed, prefer
>> >>   local, then fall back to remote if no free space.
>> >> 
>> >> - Some processes want to avoid cross-socket traffic, bind to nodes of
>> >>   local socket.
>> >> 
>> >> - Some processes want to avoid to use slow memory, bind to fast memory
>> >>   node only.
>> >
>> > Yes, I do understand that. Do you have any specific examples in mind?
>> > [...]
>> 
>> Sorry, I don't have specific examples.
>
> OK, then let's stop any complicated solution right here then. Let's
> start simple with a per-mm flag to disable demotion of an address
> space.

I'm not a big fan of per-mm flag.  Because we don't have users for that
too and it needs to add ABI too.

> Should there ever be a real demand for a more fine grained solution
> let's go further but I do not think we want a half baked solution
> without real usecases.

I'm OK to ignore per-task (and missing per-process) memory policy
support for now.

Best Regards,
Huang, Ying