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

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Message-ID: <ZU4i36tKnyXZ8lZD@tiehlicka>
Date:   Fri, 10 Nov 2023 13:32:31 +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 Fri 10-11-23 14:21:17, Huan Yang wrote:
[...]
> > BTW: how do you know the number of pages to be reclaimed proactively in
> > memcg proactive reclaiming based solution?
>
> One point here is that we are not sure how long the frozen application
> will be opened, it could be 10 minutes, an hour, or even days.  So we
> need to predict and try, gradually reclaim anonymous pages in
> proportion, preferably based on the LRU algorithm.  For example, if
> the application has been frozen for 10 minutes, reclaim 5% of
> anonymous pages; 30min:25%anon, 1hour:75%, 1day:100%.  It is even more
> complicated as it requires adding a mechanism for predicting failure
> penalties.

Why would make your reclaiming decisions based on time rather than the
actual memory demand? I can see how a pro-active reclaim could make a
head room for an unexpected memory pressure but applying more pressure
just because of inactivity sound rather dubious to me TBH. Why cannot
you simply wait for the external memory pressure (e.g. from kswapd) to
deal with that based on the demand?
-- 
Michal Hocko
SUSE Labs