linux-kernel - Re: [RFC PATCH] mm: memcg: Do not count memory.low reclaim if it does not happen

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Message-ID: <20220324095157.GA16685@blackbody.suse.cz>
Date:   Thu, 24 Mar 2022 10:51:57 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Richard Palethorpe <rpalethorpe@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Muchun Song <songmuchun@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Yang Shi <shy828301@...il.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tejun Heo <tj@...nel.org>, Chris Down <chris@...isdown.name>
Subject: Re: [RFC PATCH] mm: memcg: Do not count memory.low reclaim if it
 does not happen

On Wed, Mar 23, 2022 at 02:44:24PM -0700, Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> Does it mean that in the following configuration:
> 	`parent .low=50M
> 	  ` s1	.low=0M   .current=50M
> 	  ` s2  .low=0M   .current=50M
> there will be no memory.events::low at all? (assuming the recursive thing is on)

True, no memory.events:low among siblings.
Number of memory.events:low in the parent depends on how much has to be
reclaimed (>50M means carving into parent's protection, hence it'll be
counted).

This is a quantitative change in the events reporting (point 1 of
RFCness), my understanding is that the potential events due to recursive
surplus protection carry no new information regarding configured
memory.low.


Michal