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Wed, 21 Aug 2024 09:14:54 -0700 (PDT) Received: from blackdock.suse.cz ([193.86.92.181]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a83838cfb24sm915722966b.68.2024.08.21.09.14.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Aug 2024 09:14:54 -0700 (PDT) Date: Wed, 21 Aug 2024 18:14:52 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Yosry Ahmed Cc: Nhat Pham , Mike Yuan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, Andrew Morton , Muchun Song , Shakeel Butt , Roman Gushchin , Michal Hocko , Johannes Weiner Subject: Re: [PATCH] mm/memcontrol: respect zswap.writeback setting from parent cg too Message-ID: References: <20240814171800.23558-1-me@yhndnzj.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="lu32mhkwlc2ceo6f" Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: ojopgi3jfdhiccm71kpdio6w4n99w8tg X-Rspamd-Queue-Id: 4CA731A0014 X-Rspamd-Server: rspam11 X-HE-Tag: 1724256895-143339 X-HE-Meta: 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 xf1zK0qZ 7BpxzUwNvVBpljnhj5uBju1PfkZU3dtvYLgHWL8S+zxwKBr3REN4zsl4EaWiIMn1CP4JL+edb1so6Rqh58T3fwDmgMcTQWldzwNwV0Dl3K3UmDX6tg/NevtbhX1PsMW3gNYvzwPBd6bu+nvva+R4MOs+/gEWg+OJae8sX0OFRkx9FB2wYZcks4HmIqG3DuXYmi4yPAG6HmWShS+AE+n2rSlKLJf++EXU9cUfCL9KPBdXrXiccUPVjV/ws7TjvHL1u8JZxjMi9m/SzV8y6/QIP5BcsT/ysUYKKEOoZWo3RWUtC5+Q9c4dmCAJcHA46dvpOuk2tQFx0wlPDjPI3fuhjMfHLWGHNhJqpbUhhGayjwxmFS8yEkCC/rkAls3QdM6uJoP/VpYnd2tNSpxmT0ZxjwefR04Rge+zkuuPc5YX6G2N6qUNeCIMrdEYEWQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001045, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --lu32mhkwlc2ceo6f Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Aug 14, 2024 at 01:22:01PM GMT, Yosry Ahmed = wrote: > Anyway, both use cases make sense to me, disabling writeback > system-wide or in an entire subtree, and disabling writeback on the > root and then selectively enabling it. I am slightly inclined to the > first one (what this patch does). >=20 > Considering the hierarchical cgroup knobs work, we usually use the > most restrictive limit among the ancestors. I guess it ultimately > depends on how we define "most restrictive". Disabling writeback is > restrictive in the sense that you don't have access to free some zswap > space to reclaim more memory. OTOH, disabling writeback also means > that your zswapped memory won't go to disk under memory pressure, so > in that sense it would be restrictive to force writeback :) >=20 > Usually, the "default" is the non-restrictive thing, and then you can > set restrictions that apply to all children (e.g. no limits are set by > default). Since writeback is enabled by default, it seems like the > restriction would be disabling writeback. Hence, it would make sense > to inherit zswap disabling (i.e. only writeback if all ancestors allow > it, like this patch does). >=20 > What we do today dismisses inheritance completely, so it seems to me > like it should be changed anyway. I subscribe to inheritance (at cgroup creation) not proving well (in general). Here's the case of expecting hierarchical semantic of the attribute. With this change -- is there any point in keeping the inheritance around? (Simply default to enabled.) Thanks, Michal --lu32mhkwlc2ceo6f Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTd6mfF2PbEZnpdoAkt3Wney77BSQUCZsYSeQAKCRAt3Wney77B SexGAQCl22OTYWCFYBCcunWFQ+6cMCBJqqHzu4PPL+EdAji9RwD+NVmEGm7Wpc5h bvRkzLD1JhQDEhGkNrS7UA8ozjDdAgI= =UvMP -----END PGP SIGNATURE----- --lu32mhkwlc2ceo6f--