linux-kernel - Re: [RFC 0/4] Introduce unbalance proactive reclaim

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Date:   Fri, 10 Nov 2023 09:19:02 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Huan Yang <link@...o.com>
Cc:     Michal Hocko <mhocko@...e.com>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Jonathan Corbet" <corbet@....net>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        "Shakeel Butt" <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Peter Xu <peterx@...hat.com>,
        "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        "Liu Shixin" <liushixin2@...wei.com>,
        Hugh Dickins <hughd@...gle.com>, <cgroups@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <opensource.kernel@...o.com>
Subject: Re: [RFC 0/4] Introduce unbalance proactive reclaim

Huan Yang <link@...o.com> writes:

> 在 2023/11/9 18:39, Michal Hocko 写道:
>> [Some people who received this message don't often get email from mhocko@...e.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>
>> On Thu 09-11-23 18:29:03, Huan Yang wrote:
>>> HI Michal Hocko,
>>>
>>> Thanks for your suggestion.
>>>
>>> 在 2023/11/9 17:57, Michal Hocko 写道:
>>>> [Some people who received this message don't often get email from mhocko@...e.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>>>
>>>> On Thu 09-11-23 11:38:56, Huan Yang wrote:
>>>> [...]
>>>>>> If so, is it better only to reclaim private anonymous pages explicitly?
>>>>> Yes, in practice, we only proactively compress anonymous pages and do not
>>>>> want to touch file pages.
>>>> If that is the case and this is mostly application centric (which you
>>>> seem to be suggesting) then why don't you use madvise(MADV_PAGEOUT)
>>>> instead.
>>> Madvise  may not be applicable in this scenario.(IMO)
>>>
>>> This feature is aimed at a core goal, which is to compress the anonymous
>>> pages
>>> of frozen applications.
>>>
>>> How to detect that an application is frozen and determine which pages can be
>>> safely reclaimed is the responsibility of the policy part.
>>>
>>> Setting madvise for an application is an active behavior, while the above
>>> policy
>>> is a passive approach.(If I misunderstood, please let me know if there is a
>>> better
>>> way to set madvise.)
>> You are proposing an extension to the pro-active reclaim interface so
>> this is an active behavior pretty much by definition. So I am really not
>> following you here. Your agent can simply scan the address space of the
>> application it is going to "freeze" and call pidfd_madvise(MADV_PAGEOUT)
>> on the private memory is that is really what you want/need.
> There is a key point here. We want to use the grouping policy of memcg
> to perform
> proactive reclamation with certain tendencies. Your suggestion is to
> reclaim memory
> by scanning the task process space. However, in the mobile field,
> memory is usually
> viewed at the granularity of an APP.
>
> Therefore, after an APP is frozen, we hope to reclaim memory uniformly
> according
> to the pre-grouped APP processes.
>
> Of course, as you suggested, madvise can also achieve this, but
> implementing it in
> the agent may be more complex.(In terms of achieving the same goal,
> using memcg
> to group all the processes of an APP and perform proactive reclamation
> is simpler
> than using madvise and scanning multiple processes of an application
> using an agent?)

I still think that it's not too complex to use process_madvise() to do
this.  For each process of the application, the agent can read
/proc/PID/maps to get all anonymous address ranges, then call
process_madvise(MADV_PAGEOUT) to reclaim pages.  This can even filter
out shared anonymous pages.  Does this work for you?

--
Best Regards,
Huang, Ying