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 DFA47C433F5 for ; Fri, 1 Apr 2022 16:56:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 638178D0002; Fri, 1 Apr 2022 12:56:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5C1688D0001; Fri, 1 Apr 2022 12:56:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 461BA8D0002; Fri, 1 Apr 2022 12:56:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.27]) by kanga.kvack.org (Postfix) with ESMTP id 341CC8D0001 for ; Fri, 1 Apr 2022 12:56:32 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 02D6E220E4 for ; Fri, 1 Apr 2022 16:56:21 +0000 (UTC) X-FDA: 79308913404.09.7FF8AC7 Received: from mail-il1-f173.google.com (mail-il1-f173.google.com [209.85.166.173]) by imf01.hostedemail.com (Postfix) with ESMTP id 4856540019 for ; Fri, 1 Apr 2022 16:56:21 +0000 (UTC) Received: by mail-il1-f173.google.com with SMTP id d3so2364474ilr.10 for ; Fri, 01 Apr 2022 09:56:21 -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=AocYHkt1MbaGb+EzbKia8sCXii4deKplOa2PaIkASDE=; b=YDqVBVNEE8HcVFjurxrYb5hOycjVTxK7fOeL/e4ZGq8suMwkA1++G6q7Opq8eNnXmv alhVqf6Q7sfMLjETKtpr386gqUSGhJX2C6o2VvqlJ8p7HtB5bwcIcNB0XRLlv6htt1PB 6hec/drOZlO2WnMOaNRiPlu1yfFknBkU60wZ93cfloTZc/pNROVqNWR8vRewZz+ln2Yz GlgZw6Iv28fbArfWaavfo1YtdgqBkQ2LbR1nzQx/nUEoG9vwDenS8VHv7x3IpHv6BiGC VOvSWmSoJUdtRtes52igqYpgxtIqlBQo6hHyvFe36ewT2/HlDIhhe/hMWBPT6zWryEwJ /Aqg== 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=AocYHkt1MbaGb+EzbKia8sCXii4deKplOa2PaIkASDE=; b=6S1pKSm9E2Tm02pcNkQz3g/uR/1cLvyPFL7i7+tBw4rAPoZnbQpZED8oZCW5bqptp0 czmQuI+Y2xH4guVGlsWSqLO6tcFF/yEMWclfPf7ytWA1UJXgY0C3Q1zGrBxmq5apHd3n yJSaHdQWeW6auPmOQKamMZ7rYfB8ofrahqmfwSKJbPJ3bbuW6/+4rQa8joHgB3NEPiFz Rka5TTXbr2OLm2Jdv/05Rc+XLjFfAYkKcy6xFsAuCmtjFk8//EOmaKD+OX3yk/cwkgTN u9Bd5iSYNT1g+2ufzikVmkBgHSDiq2bT+xJ7QFi+JBfdmhn4OMJmPqKxbGAlX4QbAzAP LzFQ== X-Gm-Message-State: AOAM532L4M48mgpjRqbNTtXUmf3NDbYczBfppUxdxaJm9derf6OCDMdw Gd5suvr/sOdPnt7vd1V/Y+4C5Mi6OK6dwS5PXXOPUQ== X-Google-Smtp-Source: ABdhPJzSqAvEGZ84kfSPUS4u/aBoCuEYziFNCF1E0HAsnpfVQ8pj/c5nHIXH+rK38nN3J+0RORQPCdedCZH1BwcUCGw= X-Received: by 2002:a05:6e02:1b8f:b0:2ca:9c6:434a with SMTP id h15-20020a056e021b8f00b002ca09c6434amr342958ili.303.1648832180377; Fri, 01 Apr 2022 09:56:20 -0700 (PDT) MIME-Version: 1.0 References: <20220331084151.2600229-1-yosryahmed@google.com> In-Reply-To: From: Wei Xu Date: Fri, 1 Apr 2022 09:56:08 -0700 Message-ID: Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface To: Michal Hocko Cc: Yosry Ahmed , Johannes Weiner , 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" X-Rspam-User: X-Stat-Signature: n675uqwan953r73qkqazfndbr9my1ngm Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=YDqVBVNE; spf=pass (imf01.hostedemail.com: domain of weixugc@google.com designates 209.85.166.173 as permitted sender) smtp.mailfrom=weixugc@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4856540019 X-HE-Tag: 1648832181-439203 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 Fri, Apr 1, 2022 at 6:54 AM Michal Hocko wrote: > > On Thu 31-03-22 08:41:51, 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. > > Yes, I am for the simplicity and this really looks like a bare minumum > interface. But it is not really clear who do you want to add flags on > top of it? > > I am not really sure we really need a node aware interface for memcg. > The global reclaim interface will likely need a different node because > we do not want to make this CONFIG_MEMCG constrained. A nodemask argument for memory.reclaim can be useful for memory tiering between NUMA nodes with different performance. Similar to proactive reclaim, it can allow a userspace daemon to drive memcg-based proactive demotion via the reclaim-based demotion mechanism in the kernel. > > [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 > > All that being said. I haven't been a great fan for explicit reclaim > triggered from the userspace but I do recognize that limitations of the > existing interfaces is just too restrictive. > > Acked-by: Michal Hocko > > Thanks! > -- > Michal Hocko > SUSE Labs