From patchwork Thu Apr 21 23:44:23 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yosry Ahmed X-Patchwork-Id: 12822539 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 78BEAC433EF for ; Thu, 21 Apr 2022 23:44:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1442736AbiDUXrh (ORCPT ); Thu, 21 Apr 2022 19:47:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45824 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1442731AbiDUXrg (ORCPT ); Thu, 21 Apr 2022 19:47:36 -0400 Received: from mail-pl1-x649.google.com (mail-pl1-x649.google.com [IPv6:2607:f8b0:4864:20::649]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8D5FF47382 for ; Thu, 21 Apr 2022 16:44:44 -0700 (PDT) Received: by mail-pl1-x649.google.com with SMTP id f11-20020a170902684b00b00158c67ef30cso3291059pln.7 for ; Thu, 21 Apr 2022 16:44:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=y22yfO1Fv+K5GPJ449fnrV9G0OFkzja1qqNu/qrx2Gg=; b=hjarVUfdPQmt3pnzo7zRJoLgybwYHn7Y9qTU6JqtC269NCgTgRHX285btpNiTWP9XY g9A2o2ubpn3xZUdg6cQWwKkCTNuQ6RpTBYPaWEdU4pK2X4eBhBEQjwMWoev7/pXofYrO uTXoGA5KlhqGJ3sfVdbuzyy2wInrA7rj+5tWazekKU10XbHYVv5yNXeYfIrlb1rooGGl nQTZyTh91gn+kqYkq9HERsd37T0QX3hvXDnq7Y6tp1DZtr5YeFJfxc7eBsrEbvbnmmkX MVbx+/xOLnnAi/nvs4VjwBKUBpCJzzWGdLqLwZG1WiJc4W4hPER7dmK4vmVe9EwTskCc QqGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=y22yfO1Fv+K5GPJ449fnrV9G0OFkzja1qqNu/qrx2Gg=; b=LbygDJQakTbpJmKWAuT5J/FrNbdmnn23llrCSKhbQtZ0qhChDzPfplrPQ75p/n437O b/01G6DfmN2CNBFT6wlA2lxnXQYkf1pmoOrF8PzTO/7XH75qoZhCto6czKNYK8UB8Aqo C0NRACQ+ROKLXu941FQgAvXsPGnxcjjUcMQV2y5hCIrkHl16Ilbh+M8ZWwNYxhLVP405 WgSBgSs6FhpB72Izjumtt6UaH4R70DxONaqieGT8TwNYJZHCnWLgHUZkvjo+Wn2AnyAW Y30ThG+P87I/FMVWUu7MqYCUefLtV5PWOy31SLTsbCXSzx5d0K6m9yGKUJwkLhj+QvKp GtTQ== X-Gm-Message-State: AOAM532y6l5OwWoWzhVEg+Dl08adhtF6A1CGlYvfZnIG+Xjs4zFNcbtd id4UFZ9gmPYdqaNW1BArC7QKx8H3njBWS7qQ X-Google-Smtp-Source: ABdhPJxAlGBn6QMvn0O+++c8MJABODm4P9rbS0m7Er4vqz7yH9v9EcG6+AJKyVAYOSa0r2P19Af1jd0r4ddxLjQS X-Received: from yosry.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:2327]) (user=yosryahmed job=sendgmr) by 2002:a17:902:bc8c:b0:156:bc64:fa47 with SMTP id bb12-20020a170902bc8c00b00156bc64fa47mr1726435plb.135.1650584684042; Thu, 21 Apr 2022 16:44:44 -0700 (PDT) Date: Thu, 21 Apr 2022 23:44:23 +0000 In-Reply-To: <20220421234426.3494842-1-yosryahmed@google.com> Message-Id: <20220421234426.3494842-2-yosryahmed@google.com> Mime-Version: 1.0 References: <20220421234426.3494842-1-yosryahmed@google.com> X-Mailer: git-send-email 2.36.0.rc2.479.g8af0fa9b8e-goog Subject: [PATCH v4 1/4] memcg: introduce per-memcg reclaim interface From: Yosry Ahmed To: Johannes Weiner , Michal Hocko , Shakeel Butt , Andrew Morton , Roman Gushchin Cc: David Rientjes , 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 , Dan Schatzberg , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Yosry Ahmed , Michal Hocko Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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: refreshed to current master, updated commit message based on recent discussions and use cases] Signed-off-by: Shakeel Butt Signed-off-by: Yosry Ahmed Acked-by: Johannes Weiner Acked-by: Michal Hocko Acked-by: Wei Xu Acked-by: Roman Gushchin --- Documentation/admin-guide/cgroup-v2.rst | 21 ++++++++++++ mm/memcontrol.c | 44 +++++++++++++++++++++++++ 2 files changed, 65 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 69d7a6983f78..19bcd73cad03 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1208,6 +1208,27 @@ 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 nested-keyed file which exists for all cgroups. + + This is a simple interface to trigger memory reclaim in the + target cgroup. + + This file accepts a single key, the number of bytes to reclaim. + No nested keys are currently supported. + + Example:: + + echo "1G" > memory.reclaim + + The interface can be later extended with nested keys to + configure the reclaim behavior. For example, specify the + type of memory to reclaim from (anon, file, ..). + + Please note that the kernel can over or under reclaim from + the target cgroup. If less bytes are reclaimed than the + specified amount, -EAGAIN is returned. + 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..041c17847769 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6355,6 +6355,45 @@ 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)) + return -EINTR; + + /* This is the final attempt, drain percpu lru caches in the + * hope of introducing more evictable pages for + * try_to_free_mem_cgroup_pages(). + */ + if (!nr_retries) + lru_add_drain_all(); + + reclaimed = try_to_free_mem_cgroup_pages(memcg, + nr_to_reclaim - nr_reclaimed, + GFP_KERNEL, true); + + if (!reclaimed && !nr_retries--) + return -EAGAIN; + + nr_reclaimed += reclaimed; + } + + return nbytes; +} + static struct cftype memory_files[] = { { .name = "current", @@ -6413,6 +6452,11 @@ static struct cftype memory_files[] = { .seq_show = memory_oom_group_show, .write = memory_oom_group_write, }, + { + .name = "reclaim", + .flags = CFTYPE_NS_DELEGATABLE, + .write = memory_reclaim, + }, { } /* terminate */ };