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

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Date:   Thu, 9 Nov 2023 11:39:54 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Huan Yang <link@...o.com>
Cc:     "Huang, Ying" <ying.huang@...el.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

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.

-- 
Michal Hocko
SUSE Labs