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d=hostedemail.com; s=arc-20220608; t=1733966509; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OGGXn8bVj6X49oty/jsworxFe3cdhJmwq5ns/Yty5ss=; b=DDXBkX0iIIQKFYv5qwy25InY0OBkNxkp3MYPuC87rrJgWFbX9f4+G8mxNK3B+mO60SuzYD fvjb0pZMvjNwYhCkQ0jAiJUKv2GtHIXpIMrupAbk/A8noxmUsg3V+cEldDVnxfY9LHKwye oBjFXGEmf3o1iyePV3IZm9o5sTyMZBo= Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1tLXt7-000000006RP-1ScK; Wed, 11 Dec 2024 20:21:09 -0500 Message-ID: <1764e2fc8cff5b07aa9df1ae90a13986a3949250.camel@surriel.com> Subject: Re: [PATCH] memcg: allow exiting tasks to write back data to swap From: Rik van Riel To: Balbir Singh , Johannes Weiner Cc: Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Nhat Pham , Yosry Ahmed Date: Wed, 11 Dec 2024 20:21:08 -0500 In-Reply-To: <766a28a1-c82b-46fd-b3b0-fe3b6024f462@nvidia.com> References: <20241211105336.380cb545@fangorn> <766a28a1-c82b-46fd-b3b0-fe3b6024f462@nvidia.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.1 (3.54.1-1.fc41) MIME-Version: 1.0 X-Rspamd-Queue-Id: 8104AC0008 X-Stat-Signature: zjw96bg7sgig4yptzrskutriquzfdefr X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1733966504-632652 X-HE-Meta: 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 73rmlWJK uG9Z3OAku/snsbVMguFpMXdeDvxrFx5W3suIVPr+39EKb/Y419If6MDJpqlwxrfDqIhknXOEExndnYdJMmU/Cy5rMsYPNcx991Mc2IgG81n1442xv8STl6PqeOQm3TfIn3XUBgCeXUiUF9XUmStNYZUxpAaszt/XKmL7AB/BvY0Ht4EAIqfk1tCSpidiqBPU3AtG5Y8APaePC7Q1iWsoejidfXY9QltnhTZcL8vWwV1B4QAkej309+rx2O3yg9mCO31my8fxxbLnwLIk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2024-12-12 at 10:15 +1100, Balbir Singh wrote: > On 12/12/24 02:53, Rik van Riel wrote: > >=20 > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 7b3503d12aaf..03d77e93087e 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -5371,6 +5371,15 @@ bool > > mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg) > > =C2=A0 if (!zswap_is_enabled()) > > =C2=A0 return true; > > =C2=A0 > > + /* > > + * Always allow exiting tasks to push data to swap. A > > process in > > + * the middle of exit cannot get OOM killed, but may need > > to push > > + * uncompressible data to swap in order to get the cgroup > > memory > > + * use below the limit, and make progress with the exit. > > + */ > > + if ((current->flags & PF_EXITING) && memcg =3D=3D > > mem_cgroup_from_task(current)) > > + return true; > > + > > =C2=A0 for (; memcg; memcg =3D parent_mem_cgroup(memcg)) > > =C2=A0 if (!READ_ONCE(memcg->zswap_writeback)) > > =C2=A0 return false; >=20 > Rik, >=20 > I am unable to understand the motivation here, so we want=20 > mem_cgroup_zswap_writeback_enabled() to return true, it only > returns false if a memcg in the hierarchy has zswap_writeback > set to 0 (false). In my git-grep I can't seem to find how/why > that may be the case. I can see memcg starts of with the value > set to true, if CONFIG_ZSWAP is enabled. >=20 > Your changelog above makes sense, but I am unable to map it to > the code changes. >=20 Wait, are you asking about the code that I'm adding, or about the code that was already there? I want to add the code that allows zswap writeback if the reclaiming task is exiting, and in the same cgroup as the to be written back memory. --=20 All Rights Reversed.