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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46EE5C433F5 for ; Fri, 1 Apr 2022 09:20:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344462AbiDAJWl (ORCPT ); Fri, 1 Apr 2022 05:22:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242965AbiDAJWj (ORCPT ); Fri, 1 Apr 2022 05:22:39 -0400 Received: from mail-pl1-x62a.google.com (mail-pl1-x62a.google.com [IPv6:2607:f8b0:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D89F81F51B2 for ; Fri, 1 Apr 2022 02:20:49 -0700 (PDT) Received: by mail-pl1-x62a.google.com with SMTP id p17so1972042plo.9 for ; Fri, 01 Apr 2022 02:20:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=OMo1PXKDvOs4amOpy943mVmES4FKrWtNYVwoIwrlEW0=; b=dE6o1rYodzjxtTII77PFayYHwAYvGEuz/3yKkeKM5iYvV8dPsZmhNg2JrlVHGvoqEg L7098s00vdpVkCAhCfZoBf5ieoMJ0WbvWSpObmsBX34vbVpYN8HhJk4/0O1F4IGKgJQ5 EBmsy+JXP2q1i82SETOgFmXz8jdV+Rxw0f1W97He4sangP1hWP8kV6gWUoziezC+eBES m71DCS4rpwOd+WsQkuR7P20g6CnniuRqZpHaMi6Zm29GlSQ7oiWa/LCbJvO27w69w3Nx d1IZ2RugbuspyjLvjQM5cNntqE27YZVznZSZCABIoXbQ3ZlX4tlBz/1/tRFYHduOO81+ 7Khg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=OMo1PXKDvOs4amOpy943mVmES4FKrWtNYVwoIwrlEW0=; b=R9WqVffCHcre6HUygKSu7mtGD5v8Peqrm31XrQsTUAYdpjXr6WFYJHTr+K7MBNDWyS QVOEsY+e/3UpVYnC3tQeHTPsP6R30+8OmGFbZJkR60c038VjxKZR37XEwZOz8JL9Lh6X 7XBNoQIx7UZ7f4Jhc6ComIJSHR2AJXKmUxD5r2avmJ0lhOhuQavkRA3KywzMDVaEqbUK f2T5J86eyIYWaphM44kvXJHLxQkkBNuW4HnBPcdxCin4o89lfY988J1vPXh5r+jYIg0H kUfBX7OZZgNKHnEAjG8P9USIF0GQXDaqcgaq4BBDl7RS3mKTdgeOLm9LBLGEjHi33ANl IT8Q== X-Gm-Message-State: AOAM5311K5wxCaZ85OIQin7tFnmNLwxT8wnCDbUZ/ylfZ3csNxajDwfj KKp8UdbO5fM2oG50Zo4XdDBhgb1zGsTtkvGYbZ7YZA== X-Google-Smtp-Source: ABdhPJybip9dLqp8JkI+BR/GtYsKkhXxH6DoUYJfaCaqf9bJQ8jopCzfQsXkGV0AuBeWQM4VMb1K2rhGA5GfRcaXdvk= X-Received: by 2002:a17:90b:3886:b0:1c7:c935:4447 with SMTP id mu6-20020a17090b388600b001c7c9354447mr10955042pjb.196.1648804849057; Fri, 01 Apr 2022 02:20:49 -0700 (PDT) MIME-Version: 1.0 References: <20220331084151.2600229-1-yosryahmed@google.com> <2025405d-c32b-338a-b668-48b07a34e4ef@huawei.com> In-Reply-To: <2025405d-c32b-338a-b668-48b07a34e4ef@huawei.com> From: Yosry Ahmed Date: Fri, 1 Apr 2022 02:20:12 -0700 Message-ID: Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface To: Chen Wandun Cc: Johannes Weiner , Michal Hocko , Shakeel Butt , Andrew Morton , David Rientjes , Tejun Heo , Zefan Li , Roman Gushchin , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Linux-MM , Jonathan Corbet , Yu Zhao , Dave Hansen , Wei Xu , Greg Thelen Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 31, 2022 at 8:05 PM Chen Wandun wrote: > > > > =E5=9C=A8 2022/3/31 16:41, Yosry Ahmed =E5=86=99=E9=81=93: > > From: Shakeel Butt > > > > Introduce an memcg interface to trigger memory reclaim on a memory cgro= up. > > > > Use case: Proactive Reclaim > > --------------------------- > > > > A userspace proactive reclaimer can continuously probe the memcg to > > reclaim a small amount of memory. This gives more accurate and > > up-to-date workingset estimation as the LRUs are continuously > > sorted and can potentially provide more deterministic memory > > overcommit behavior. The memory overcommit controller can provide > > more proactive response to the changing behavior of the running > > applications instead of being reactive. > > > > A userspace reclaimer's purpose in this case is not a complete replacem= ent > > for kswapd or direct reclaim, it is to proactively identify memory savi= ngs > > opportunities and reclaim some amount of cold pages set by the policy > > to free up the memory for more demanding jobs or scheduling new jobs. > > > > A user space proactive reclaimer is used in Google data centers. > > Additionally, Meta's TMO paper recently referenced a very similar > > interface used for user space proactive reclaim: > > https://dl.acm.org/doi/pdf/10.1145/3503222.3507731 > > > > Benefits of a user space reclaimer: > > ----------------------------------- > > > > 1) More flexible on who should be charged for the cpu of the memory > > reclaim. For proactive reclaim, it makes more sense to be centralized. > > > > 2) More flexible on dedicating the resources (like cpu). The memory > > overcommit controller can balance the cost between the cpu usage and > > the memory reclaimed. > > > > 3) Provides a way to the applications to keep their LRUs sorted, so, > > under memory pressure better reclaim candidates are selected. This also > > gives more accurate and uptodate notion of working set for an > > application. > > > > Why memory.high is not enough? > > ------------------------------ > > > > - memory.high can be used to trigger reclaim in a memcg and can > > potentially be used for proactive reclaim. > > However there is a big downside in using memory.high. It can potenti= ally > > introduce high reclaim stalls in the target application as the > > allocations from the processes or the threads of the application can= hit > > the temporary memory.high limit. > > > > - Userspace proactive reclaimers usually use feedback loops to decide > > how much memory to proactively reclaim from a workload. The metrics > > used for this are usually either refaults or PSI, and these metrics > > will become messy if the application gets throttled by hitting the > > high limit. > > > > - memory.high is a stateful interface, if the userspace proactive > > reclaimer crashes for any reason while triggering reclaim it can lea= ve > > the application in a bad state. > > > > - If a workload is rapidly expanding, setting memory.high to proactivel= y > > reclaim memory can result in actually reclaiming more memory than > > intended. > > > > The benefits of such interface and shortcomings of existing interface > > were further discussed in this RFC thread: > > https://lore.kernel.org/linux-mm/5df21376-7dd1-bf81-8414-32a73cea45dd@g= oogle.com/ > > > > Interface: > > ---------- > > > > Introducing a very simple memcg interface 'echo 10M > memory.reclaim' t= o > > trigger reclaim in the target memory cgroup. > > > > > > Possible Extensions: > > -------------------- > > > > - This interface can be extended with an additional parameter or flags > > to allow specifying one or more types of memory to reclaim from (e.g= . > > file, anon, ..). > > > > - The interface can also be extended with a node mask to reclaim from > > specific nodes. This has use cases for reclaim-based demotion in mem= ory > > tiering systens. > > > > - A similar per-node interface can also be added to support proactive > > reclaim and reclaim-based demotion in systems without memcg. > > > > For now, let's keep things simple by adding the basic functionality. > > > > [yosryahmed@google.com: refreshed to current master, updated commit > > message based on recent discussions and use cases] > > Signed-off-by: Shakeel Butt > > Signed-off-by: Yosry Ahmed > > --- > > Documentation/admin-guide/cgroup-v2.rst | 9 ++++++ > > mm/memcontrol.c | 37 ++++++++++++++++++++++++= + > > 2 files changed, 46 insertions(+) > > > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/ad= min-guide/cgroup-v2.rst > > index 69d7a6983f78..925aaabb2247 100644 > > --- a/Documentation/admin-guide/cgroup-v2.rst > > +++ b/Documentation/admin-guide/cgroup-v2.rst > > @@ -1208,6 +1208,15 @@ PAGE_SIZE multiple when read back. > > high limit is used and monitored properly, this limit's > > utility is limited to providing the final safety net. > > > > + memory.reclaim > > + A write-only file which exists on non-root cgroups. > > + > > + This is a simple interface to trigger memory reclaim in the > > + target cgroup. Write the number of bytes to reclaim to this > > + file and the kernel will try to reclaim that much memory. > > + Please note that the kernel can over or under reclaim from > > + the target cgroup. > > + > > memory.oom.group > > A read-write single value file which exists on non-root > > cgroups. The default value is "0". > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 725f76723220..994849fab7df 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -6355,6 +6355,38 @@ static ssize_t memory_oom_group_write(struct ker= nfs_open_file *of, > > return nbytes; > > } > > > > +static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, > > + size_t nbytes, loff_t off) > > +{ > > + struct mem_cgroup *memcg =3D mem_cgroup_from_css(of_css(of)); > > + unsigned int nr_retries =3D MAX_RECLAIM_RETRIES; > > + unsigned long nr_to_reclaim, nr_reclaimed =3D 0; > > + int err; > > + > > + buf =3D strstrip(buf); > > + err =3D page_counter_memparse(buf, "", &nr_to_reclaim); > > + if (err) > > + return err; > > + > > + while (nr_reclaimed < nr_to_reclaim) { > > + unsigned long reclaimed; > > + > > + if (signal_pending(current)) > > + break; > > + > > + reclaimed =3D try_to_free_mem_cgroup_pages(memcg, > > + nr_to_reclaim - nr_reclai= med, > > + GFP_KERNEL, true); > In some scenario there are lots of page cache, and we only want to > reclaim page cache, > how about add may_swap option? Thanks for taking a look at this! The first listed extension is an argument/flags to specify the type of memory that we want to reclaim, I think this covers this use case, or am I missing something? > > + > > + if (!reclaimed && !nr_retries--) > > + break; > > + > > + nr_reclaimed +=3D reclaimed; > > + } > > + > > + return nbytes; > > +} > > + > > static struct cftype memory_files[] =3D { > > { > > .name =3D "current", > > @@ -6413,6 +6445,11 @@ static struct cftype memory_files[] =3D { > > .seq_show =3D memory_oom_group_show, > > .write =3D memory_oom_group_write, > > }, > > + { > > + .name =3D "reclaim", > > + .flags =3D CFTYPE_NOT_ON_ROOT | CFTYPE_NS_DELEGATABLE, > > + .write =3D memory_reclaim, > > + }, > > { } /* terminate */ > > }; > > >