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 DF603C433F5 for ; Mon, 25 Apr 2022 19:15:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 38EE96B0092; Mon, 25 Apr 2022 15:15:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 33D156B0093; Mon, 25 Apr 2022 15:15:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1DD756B0095; Mon, 25 Apr 2022 15:15:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id 0C48B6B0092 for ; Mon, 25 Apr 2022 15:15:52 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id AC9D5246C for ; Mon, 25 Apr 2022 19:15:51 +0000 (UTC) X-FDA: 79396356102.26.0D82F83 Received: from mail-pj1-f45.google.com (mail-pj1-f45.google.com [209.85.216.45]) by imf11.hostedemail.com (Postfix) with ESMTP id A10EB4003B for ; Mon, 25 Apr 2022 19:15:48 +0000 (UTC) Received: by mail-pj1-f45.google.com with SMTP id bd19-20020a17090b0b9300b001d98af6dcd1so216118pjb.4 for ; Mon, 25 Apr 2022 12:15:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:in-reply-to:message-id:references :mime-version; bh=ecsUxmyFwe8I77x+9cA1HTTii6mLSDL9ggSg8/7/5Lo=; b=lSv3D+xXudt8kuycOWKphR/+PTAKkjLYPnzKliiGicQEjNUPwftnMMBs2cG9pNFHPV Rx5m56PnLtd6rUJslmzMmG0HpEdKW4PPVfBjF3VEMO4+y8q8bkRuqgB6GFRLiMtUC//+ dIID5FA51QMkhLndJJnDP4lfVmsSD3tZw1djRdoRfaC+JPv8o1fwE6rkxfTqwELj3BHr mXgDscQMSgJLeW+ALlwLXot4+PkLBbSajgNXMds+bAuLTm3k9Vn2cCn7eblMwAcCVs5g 1aPwVBuFa8VfQ32WIX08L2Ouzo2vqpTVIC81Gj14Rz1jpg4RvV3la7P2rAGcA5/ySaJV hj/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:mime-version; bh=ecsUxmyFwe8I77x+9cA1HTTii6mLSDL9ggSg8/7/5Lo=; b=gT8B+Z3gg/W8/gL6RlsLfAWskpFqVb4SapFHGF+mVV+3NuYTESi/5BGPOBjbjHOKMh P9YnezmgMQ06v93ZUtm5mVM1lD03uWJvK6OvotA/anjlHXMp4L/+H1SOjro/KXs0qqDK pc2T+LhbLfSCpnjVMn3fzTD3tWvk193QJgVjG4BohUoY+uYh295DuawJ+9Tgb3ke5L0A 9Aam6fcZzcVV0UWm2moZ2bYdKxHRJPj59S/fqJ9yHG3iIh6MftBv7Sw3fJfhuhcwmuJo r2/gEUMq6HmD4xdtEnXvTypA/SBwjrHz1a03mX+sJMgtz0yCcuKlig/r6wu9E34W3FWe eMDg== X-Gm-Message-State: AOAM533GH5eghE+EL+LIxu4VRXj9pyyTCGOmJdMx8fd8hl0p+OLUzGMb yLXCPN0ri1PCd73mzRhZLRLytw== X-Google-Smtp-Source: ABdhPJxVDk2aBeKX93y2/cNj0dtdmux5xztwRbAL9FG9GNAcURiUqYol+3kkAIs0S0BKpuya0KJacA== X-Received: by 2002:a17:90a:b10c:b0:1d9:49de:81c5 with SMTP id z12-20020a17090ab10c00b001d949de81c5mr12523263pjq.120.1650914149899; Mon, 25 Apr 2022 12:15:49 -0700 (PDT) Received: from [2620:15c:29:204:185b:8dcc:84d4:fb71] ([2620:15c:29:204:185b:8dcc:84d4:fb71]) by smtp.gmail.com with ESMTPSA id i11-20020a654d0b000000b0039d82c3e68csm10711275pgt.55.2022.04.25.12.15.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Apr 2022 12:15:49 -0700 (PDT) Date: Mon, 25 Apr 2022 12:15:48 -0700 (PDT) From: David Rientjes To: Yosry Ahmed cc: Johannes Weiner , Michal Hocko , Shakeel Butt , Andrew Morton , Roman Gushchin , Tejun Heo , Zefan Li , Jonathan Corbet , Shuah Khan , Yu Zhao , Dave Hansen , Wei Xu , Greg Thelen , Chen Wandun , Vaibhav Jain , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Tim Chen , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Michal Hocko Subject: Re: [PATCH v5 1/4] memcg: introduce per-memcg reclaim interface In-Reply-To: <20220425190040.2475377-2-yosryahmed@google.com> Message-ID: References: <20220425190040.2475377-1-yosryahmed@google.com> <20220425190040.2475377-2-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: fq5e6i3uhxxpxpkfs69qx4dk9ndcpfis X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A10EB4003B X-Rspam-User: Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=lSv3D+xX; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf11.hostedemail.com: domain of rientjes@google.com designates 209.85.216.45 as permitted sender) smtp.mailfrom=rientjes@google.com X-HE-Tag: 1650914148-290248 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 Mon, 25 Apr 2022, Yosry Ahmed wrote: > From: Shakeel Butt > > Introduce a 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. > > The interface is introduced as a nested-keyed file to allow for future > optional arguments to be easily added to configure the behavior of > reclaim. > > 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. > > - Add a timeout parameter to make it easier for user space to call the > interface without worrying about being blocked for an undefined amount > of time. > > For now, let's keep things simple by adding the basic functionality. > > [yosryahmed@google.com: worked on versions v2 onwards, refreshed to > current master, updated commit message based on recent > discussions and use cases] > > Signed-off-by: Shakeel Butt > Co-developed-by: Yosry Ahmed > Signed-off-by: Yosry Ahmed > Acked-by: Johannes Weiner > Acked-by: Michal Hocko > Acked-by: Wei Xu > Acked-by: Roman Gushchin Acked-by: David Rientjes "can over or under reclaim from the target cgroup" begs the question of how much more memory the kernel can decide to reclaim :) I think it's assumed that it's minimal and that matches the current implementation that rounds up to SWAP_CLUSTER_MAX, though, so looks good. Thanks Yosry!