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 EFD4CC433F5 for ; Fri, 1 Apr 2022 09:22:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 80D4A8D0002; Fri, 1 Apr 2022 05:22:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7BD2D8D0001; Fri, 1 Apr 2022 05:22:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 684CC8D0002; Fri, 1 Apr 2022 05:22:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0244.hostedemail.com [216.40.44.244]) by kanga.kvack.org (Postfix) with ESMTP id 583D98D0001 for ; Fri, 1 Apr 2022 05:22:49 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 216F1A5D2E for ; Fri, 1 Apr 2022 09:22:39 +0000 (UTC) X-FDA: 79307770038.27.F157A89 Received: from mail-pf1-f170.google.com (mail-pf1-f170.google.com [209.85.210.170]) by imf27.hostedemail.com (Postfix) with ESMTP id 9F87D40020 for ; Fri, 1 Apr 2022 09:22:38 +0000 (UTC) Received: by mail-pf1-f170.google.com with SMTP id s11so2065352pfu.13 for ; Fri, 01 Apr 2022 02:22:38 -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; bh=EyRExLAQW3m/1gMlz2hctnqaSl+H0AAJm330r3O/ZwY=; b=JEtAlBR0JyfJM25DDuiGeSo9iIQUhiRgfxKW6UMpgaCmRtDZmRf7mrFS2Jljti8Lot b3lw9HymXOrt7JC8DZRPFC0nCkdmRNMQosI3Wqb+kFk0fwjxT5Pc77yEHtjchA2bK/wH 14rXfmGFBZ8b5lvOB9Hq+gJJo2RZUJLt7iWD+aMxkZhjD6xSa/1JQgtXgMVTotg7DpiX LEzB9jdJRxLen+/a8Df00++pQe8TmjoS9qG8zBXYU+J1KRhvQTVhpqbv2Op+/Y9StY2K 2SPRieOpDwK+yK5c66n49IL1TB4UUIgbeUZHBHNlhDAbGxLKOQaWrbKLaNmk5KNzSmrT EpDw== 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; bh=EyRExLAQW3m/1gMlz2hctnqaSl+H0AAJm330r3O/ZwY=; b=6tSkttfYRnM9PFqhetx4kfkbEpoE4bv0vjqJRJkJnrvrVocAdyc/PJpOKncovmi52k 8ewDi0jqRDBVxLeQI1V5noh3c9h+RZ5uwLSLTjFrFK34gXeNCL9MrcNyp8C5HIB4JwxV kZj+X6EQjIfK6faM7WclnsE/Oqqie1yYqKTY4qMf1Qkgj8ft+OFdbvYdsaEpNkVWCPfj jCfbxdwV6svqw9v/oVwoRLTxJmAARREXkdRfoax4pgJ1O/BWyKtEYdEnDfb1zg9XBirE E7/TNCh2d7AxJeOboWcHfM13Mlt7dfVcMEGIjxsF20RKprljJx6/ATH+lOfpMIw0k91N cNhQ== X-Gm-Message-State: AOAM531F+rxDY9r4HbOupgJ4oMXXAMf1ccYeEH2zW6m0saMti50Ab17S cqECTUSV9bBOs5h2IbJrJy9DReSclbdKh/BvEx/5Sw== X-Google-Smtp-Source: ABdhPJzPGK4Wj1VbuaKgyrD4+BY+Qz1wmT91honIjqxq6dAiJYfDQEjCcolwiIjZtcqpipZcLmNYSGbhlVu79xmax40= X-Received: by 2002:a05:6a00:a0f:b0:4e1:309:83c0 with SMTP id p15-20020a056a000a0f00b004e1030983c0mr9865708pfh.68.1648804957383; Fri, 01 Apr 2022 02:22:37 -0700 (PDT) MIME-Version: 1.0 References: <20220331084151.2600229-1-yosryahmed@google.com> In-Reply-To: From: Yosry Ahmed Date: Fri, 1 Apr 2022 02:22:01 -0700 Message-ID: Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface To: Wei Xu 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 Mailing List , Linux MM , Jonathan Corbet , Yu Zhao , Dave Hansen , Greg Thelen Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=JEtAlBR0; spf=pass (imf27.hostedemail.com: domain of yosryahmed@google.com designates 209.85.210.170 as permitted sender) smtp.mailfrom=yosryahmed@google.com; dmarc=pass (policy=reject) header.from=google.com X-Stat-Signature: f9xgkmxerdezw5ryu7m3y3hajy43oo61 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9F87D40020 X-HE-Tag: 1648804958-451034 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 Thu, Mar 31, 2022 at 9:05 PM Wei Xu wrote: > > On Thu, Mar 31, 2022 at 1:42 AM Yosry Ahmed wrote: > > > > From: Shakeel Butt > > > > Introduce an memcg interface to trigger memory reclaim on a memory cgroup. > > > > 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 replacement > > for kswapd or direct reclaim, it is to proactively identify memory savings > > 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 potentially > > 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 leave > > the application in a bad state. > > > > - If a workload is rapidly expanding, setting memory.high to proactively > > 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@google.com/ > > > > Interface: > > ---------- > > > > Introducing a very simple memcg interface 'echo 10M > memory.reclaim' to > > 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 memory > > 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/admin-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 kernfs_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 = mem_cgroup_from_css(of_css(of)); > > + unsigned int nr_retries = MAX_RECLAIM_RETRIES; > > + unsigned long nr_to_reclaim, nr_reclaimed = 0; > > + int err; > > + > > + buf = strstrip(buf); > > + err = 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 = try_to_free_mem_cgroup_pages(memcg, > > + nr_to_reclaim - nr_reclaimed, > > + GFP_KERNEL, true); > > + > > + if (!reclaimed && !nr_retries--) > > + break; > > + > > + nr_reclaimed += reclaimed; > > + } > > + > > + return nbytes; > > It is better to return an error code (e.g. -EBUSY) when > memory_reclaim() fails to reclaim nr_to_reclaim bytes of memory, > except if the cgroup memory usage is already 0. We can also return > -EINVAL if nr_to_reclaim is too large (e.g. > limit). IIUC this interface is modeled after memory.high, which returns nbytes as well. If you think it's better here to do this instead of maintaining consistency with memory.high we can certainly do this for v2. > > > +} > > + > > static struct cftype memory_files[] = { > > { > > .name = "current", > > @@ -6413,6 +6445,11 @@ static struct cftype memory_files[] = { > > .seq_show = memory_oom_group_show, > > .write = memory_oom_group_write, > > }, > > + { > > + .name = "reclaim", > > + .flags = CFTYPE_NOT_ON_ROOT | CFTYPE_NS_DELEGATABLE, > > + .write = memory_reclaim, > > + }, > > { } /* terminate */ > > }; > > > > -- > > 2.35.1.1021.g381101b075-goog > >