From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0066C352A1 for ; Wed, 7 Dec 2022 01:58:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 18BB38E0005; Tue, 6 Dec 2022 20:58:18 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 13C738E0001; Tue, 6 Dec 2022 20:58:18 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F1E628E0005; Tue, 6 Dec 2022 20:58:17 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id E18D28E0001 for ; Tue, 6 Dec 2022 20:58:17 -0500 (EST) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id B65B3AB125 for ; Wed, 7 Dec 2022 01:58:17 +0000 (UTC) X-FDA: 80213850234.24.48A6594 Received: from mail-oa1-f46.google.com (mail-oa1-f46.google.com [209.85.160.46]) by imf08.hostedemail.com (Postfix) with ESMTP id 6F577160007 for ; Wed, 7 Dec 2022 01:58:17 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=eBRBdaHX; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf08.hostedemail.com: domain of hughd@google.com designates 209.85.160.46 as permitted sender) smtp.mailfrom=hughd@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1670378297; h=from:from: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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=L8963QVuWzMlre8yLN4891ujCBmWo5SyqcLZ8tSbZjQ=; b=TmfDNGA9snLg2k7gQEan7UqhuSxOlpSglDhFFPKMpO/2vb3Dz8ctKSrlOdVxqhAtqEMikx dSvwqEcTY8rREdl/FLauTM+qX1Z2/BAB0cT6b0bnUb3+urjF5sVWrX0/Op7tuTkot+02QR bbMeYr4NE+jxCpfPalYhsDL3vXuttN4= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=eBRBdaHX; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf08.hostedemail.com: domain of hughd@google.com designates 209.85.160.46 as permitted sender) smtp.mailfrom=hughd@google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1670378297; a=rsa-sha256; cv=none; b=bQszdURF9lJPAACGtseLmTX/v0FQRa8Qczd1ZGyxQju2LULZykLADs2hVfbUJk1rF1chtd jjPRUxSegXcN1q+dCBSpMJgaArBO532Z5xU9gkuX4oxv3ND/fSERcUHeW9mWcJzH6tAoLp h+hx7Pn/fkCBUa8AZdYrNB+1yGOHBog= Received: by mail-oa1-f46.google.com with SMTP id 586e51a60fabf-144bd860fdbso6550802fac.0 for ; Tue, 06 Dec 2022 17:58:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=L8963QVuWzMlre8yLN4891ujCBmWo5SyqcLZ8tSbZjQ=; b=eBRBdaHXvgKpW6/nBEGd/saUzFoozLpzIKQmkJccf22pFYLqqUwQmUXP7zz+NHarWr y6oNwxxTkbGSuO+M05BGsjg+XcnEor7+ZxHUaOF9F0dTgXN7JIhH9mxY69OxgcpyIJtb qj/GNdr7md0XD0zM0Hpy6wzMv9vqEvJfEd51lxXbNqMjf1P3z2dC4uoPY6R4fKcFL2FB 9h3S323dKwW0PyiDSM/OYs9Vn6du77A0CRL7M/dX4DwA8nNcujWN5Rkdp2SbA9XC6Lsj UTrD1polfnjmptxxWF4CLi5v3jR2pGansFPDF0QCUdjds6TL4/tG/rF5tcpCKINWjhf6 5Gaw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=L8963QVuWzMlre8yLN4891ujCBmWo5SyqcLZ8tSbZjQ=; b=Lmjt+kg9JGy5FCnG0n78oBSwCnwCSJxKWSr5VzlwVb4ToWhbp63t5OioTLAhHUGKey Npzddp8nZg5xhm/Gm9trOaEeW6yUyl+O8SvaK8ttX+Pn7vdGUZ00bXsTyuaGJuiUe330 dQg1ZH1BNbjsixwBusHIaYCRWIlnpkhci/ftYnybjrsub9/PhMn1gntl/3ax1CHe3lvC SOAkkTPo+/x60pI2/WWjERZrQrARyGoxsdXp7puX8JZB+GK5ZXkDK0VVvyfpB5V80zzz w8IT02prhqFApePqtf6XK7KMVxw5lETyXqk0/4LBT9o2Z5dXYcCOdSvn8M/LyK8XOW6f p72A== X-Gm-Message-State: ANoB5pkAYbPtbKhN2DhDxPjHku6f7qfwuLp6g/Uw4NQAFKb84zRRpEQw NfEbeD5/xKmobtR+1QcAJpFuYA== X-Google-Smtp-Source: AA0mqf5/RI59FAboxfx2566HImOLKq9uSfCZXsGND07TLSEOb93NMRKIOCrF49q2VX8skzs0kz/enw== X-Received: by 2002:a05:6870:8882:b0:132:6f79:9ffb with SMTP id m2-20020a056870888200b001326f799ffbmr41793603oam.61.1670378296550; Tue, 06 Dec 2022 17:58:16 -0800 (PST) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id k7-20020a056830168700b006705cddb73fsm1205278otr.31.2022.12.06.17.58.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Dec 2022 17:58:16 -0800 (PST) Date: Tue, 6 Dec 2022 17:58:14 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Johannes Weiner cc: Andrew Morton , Linus Torvalds , Hugh Dickins , Shakeel Butt , Michal Hocko , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] mm: memcontrol: deprecate charge moving In-Reply-To: <20221206171340.139790-4-hannes@cmpxchg.org> Message-ID: <02b9663-4377-bd67-8da2-aad72240da@google.com> References: <20221206171340.139790-1-hannes@cmpxchg.org> <20221206171340.139790-4-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6F577160007 X-Stat-Signature: 9jr8mcufyrisqtzepymbe6mgrd4em7fu X-Spamd-Result: default: False [-2.90 / 9.00]; BAYES_HAM(-6.00)[100.00%]; SORBS_IRL_BL(3.00)[209.85.160.46:from]; MIME_GOOD(-0.10)[text/plain]; RCVD_NO_TLS_LAST(0.10)[]; BAD_REP_POLICIES(0.10)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; DMARC_POLICY_ALLOW(0.00)[google.com,reject]; DKIM_TRACE(0.00)[google.com:+]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; R_SPF_ALLOW(0.00)[+ip4:209.85.128.0/17]; RCVD_COUNT_THREE(0.00)[3]; R_DKIM_ALLOW(0.00)[google.com:s=20210112]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; PREVIOUSLY_DELIVERED(0.00)[linux-mm@kvack.org]; RCVD_VIA_SMTP_AUTH(0.00)[] X-HE-Tag: 1670378297-367234 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: On Tue, 6 Dec 2022, Johannes Weiner wrote: > Charge moving mode in cgroup1 allows memory to follow tasks as they > migrate between cgroups. This is, and always has been, a questionable > thing to do - for several reasons. > > First, it's expensive. Pages need to be identified, locked and > isolated from various MM operations, and reassigned, one by one. > > Second, it's unreliable. Once pages are charged to a cgroup, there > isn't always a clear owner task anymore. Cache isn't moved at all, for > example. Mapped memory is moved - but if trylocking or isolating a > page fails, it's arbitrarily left behind. Frequent moving between > domains may leave a task's memory scattered all over the place. > > Third, it isn't really needed. Launcher tasks can kick off workload > tasks directly in their target cgroup. Using dedicated per-workload > groups allows fine-grained policy adjustments - no need to move tasks > and their physical pages between control domains. The feature was > never forward-ported to cgroup2, and it hasn't been missed. > > Despite it being a niche usecase, the maintenance overhead of > supporting it is enormous. Because pages are moved while they are live > and subject to various MM operations, the synchronization rules are > complicated. There are lock_page_memcg() in MM and FS code, which > non-cgroup people don't understand. In some cases we've been able to > shift code and cgroup API calls around such that we can rely on native > locking as much as possible. But that's fragile, and sometimes we need > to hold MM locks for longer than we otherwise would (pte lock e.g.). > > Mark the feature deprecated. Hopefully we can remove it soon. > > Signed-off-by: Johannes Weiner Acked-by: Hugh Dickins but I wonder if it would be helpful to mention move_charge_at_immigrate in the deprecation message: maybe the first line should be "Cgroup memory moving (move_charge_at_immigrate) is deprecated.\n" > --- > Documentation/admin-guide/cgroup-v1/memory.rst | 11 ++++++++++- > mm/memcontrol.c | 4 ++++ > 2 files changed, 14 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst > index 60370f2c67b9..87d7877b98ec 100644 > --- a/Documentation/admin-guide/cgroup-v1/memory.rst > +++ b/Documentation/admin-guide/cgroup-v1/memory.rst > @@ -86,6 +86,8 @@ Brief summary of control files. > memory.swappiness set/show swappiness parameter of vmscan > (See sysctl's vm.swappiness) > memory.move_charge_at_immigrate set/show controls of moving charges > + This knob is deprecated and shouldn't be > + used. > memory.oom_control set/show oom controls. > memory.numa_stat show the number of memory usage per numa > node > @@ -717,9 +719,16 @@ Soft limits can be setup by using the following commands (in this example we > It is recommended to set the soft limit always below the hard limit, > otherwise the hard limit will take precedence. > > -8. Move charges at task migration > +8. Move charges at task migration (DEPRECATED!) > ================================= > > +THIS IS DEPRECATED! > + > +It's expensive and unreliable! It's better practice to launch workload > +tasks directly from inside their target cgroup. Use dedicated workload > +cgroups to allow fine-grained policy adjustments without having to > +move physical pages between control domains. > + > Users can move charges associated with a task along with task migration, that > is, uncharge task's pages from the old cgroup and charge them to the new cgroup. > This feature is not supported in !CONFIG_MMU environments because of lack of > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index b696354c1b21..e650a38d9a90 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3919,6 +3919,10 @@ static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css, > { > struct mem_cgroup *memcg = mem_cgroup_from_css(css); > > + pr_warn_once("Cgroup memory moving is deprecated. " > + "Please report your usecase to linux-mm@kvack.org if you " > + "depend on this functionality.\n"); > + > if (val & ~MOVE_MASK) > return -EINVAL; > > -- > 2.38.1 > >