Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Subject: Re: [RFC PATCH] mm: memcg: Do not count memory.low reclaim if it does not happen
From:   Roman Gushchin <roman.gushchin@linux.dev>
In-Reply-To: <20220324095157.GA16685@blackbody.suse.cz>
Date:   Thu, 24 Mar 2022 11:17:14 -0700
Cc:     cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Richard Palethorpe <rpalethorpe@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shakeel Butt <shakeelb@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Yang Shi <shy828301@gmail.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Tejun Heo <tj@kernel.org>, Chris Down <chris@chrisdown.name>
Message-Id: <5049EBC3-5BAE-4509-BA63-1F4A7D913517@linux.dev>
References: <20220324095157.GA16685@blackbody.suse.cz>
To:     =?utf-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Precedence: bulk


> On Mar 24, 2022, at 2:52 AM, Michal Koutn=C3=BD <mkoutny@suse.com> wrote:
>=20
> =EF=BB=BFOn Wed, Mar 23, 2022 at 02:44:24PM -0700, Roman Gushchin <roman.g=
ushchin@linux.dev> wrote:
>> Does it mean that in the following configuration:
>>    `parent .low=3D50M
>>      ` s1    .low=3D0M   .current=3D50M
>>      ` s2  .low=3D0M   .current=3D50M
>> there will be no memory.events::low at all? (assuming the recursive thing=
 is on)
>=20
> 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).

Ok, so it=E2=80=99s not really about the implementation details of the recla=
im mechanism (I mean rounding up to the batch size etc), it=E2=80=99s a more=
 generic change: do not generate low events for cgroups not explicitly prote=
cted by a non-zero memory.low value.

Idk, I don=E2=80=99t have a strong argument against this change (except that=
 it changes the existing behavior), but I also don=E2=80=99t see why such ev=
ents are harmful. Do you mind elaborating a bit more?

Thank you!=