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 7AF60C433EF for ; Fri, 1 Apr 2022 04:05:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238308AbiDAEHW (ORCPT ); Fri, 1 Apr 2022 00:07:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233366AbiDAEHR (ORCPT ); Fri, 1 Apr 2022 00:07:17 -0400 Received: from mail-io1-xd2f.google.com (mail-io1-xd2f.google.com [IPv6:2607:f8b0:4864:20::d2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BEEF73E5F7 for ; Thu, 31 Mar 2022 21:05:27 -0700 (PDT) Received: by mail-io1-xd2f.google.com with SMTP id p21so1904288ioj.4 for ; Thu, 31 Mar 2022 21:05:27 -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=B+CLss0WbItuifu72dHflWYaudPs9OpOIrtnBZ+LuaU=; b=W4lP36K+Sb0fsBGicZNNHA2PdXSFLxGLOGu+QIo0Pr+K09Bfb/JQ9y7h29SJTwHCkL qo9Meye8l/bh5ZdCafGJlboKfyAh3OTCZiwV615CLHt7foV27/crahdWIZpXP9o5zyDT f4B0knRfleCmNsT7S/1gVtK/jnuLe8dMnvgnkEw7P3BsrmJSWJR0z6u8myMWpvrwhycC K0MJjUxswzx2hsClKurU0lxBklqJnt5jCMfdXO/WkmQApUMQX+vefGDz6SReFNqKkDvo OLqXgs1GpET++yDSsieKbkumlNIePUfHJvkrEdI24CUoKeH4Ge+57mvK0e8QEpJiPpQ6 0WeQ== 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=B+CLss0WbItuifu72dHflWYaudPs9OpOIrtnBZ+LuaU=; b=QbWFL6n44ViWDHZZ8cd7Eeswi1RmX6Kuwtu5Gvb0L1ZMZ8A05lo+wFZiumK/xfh9c7 P1dpXQWOeTHk2vWWPQmSuz7amltKDhPDxfGLjPJsVkA6t+a4z3R+qjU1E/jAs9znHrwS fUKX9b3PLxOGR+/XlibwH4uXiL0saGKySbQ8ncYr0F/FSTL99b22WMnWKyUrOS5JnvS+ VhHh7XpqdSgiTWuOV5vZ8LPgZ4jEFsCAouNjDZi+AYm8Hezed/uweGRdZ7U9c/842Uw9 vmAqHgFXoGHesOvFaWYl4EGSGr+yUMmjyJzZjPaxw5bIUsIxWCjKFAFn0Y4wnwPHYwf8 fhUQ== X-Gm-Message-State: AOAM533ACwNcPw3LG4w/5Uggu8tCdwOYNdNS3ALG6p/nIehq1xRk1rcg YOSa13Nhl5VxwOTbcTGltg+ddGU4nLIfJ7Yov9Rbgw== X-Google-Smtp-Source: ABdhPJxTpgpr2IYgcO6o0NsQkkbran/YiQB177+6APQAT+EOzydrNcz9ySUynHUNFST25lY4tTlWweAtwwYoDAybsGU= X-Received: by 2002:a05:6638:4128:b0:323:62b4:30c3 with SMTP id ay40-20020a056638412800b0032362b430c3mr4994319jab.318.1648785926987; Thu, 31 Mar 2022 21:05:26 -0700 (PDT) MIME-Version: 1.0 References: <20220331084151.2600229-1-yosryahmed@google.com> In-Reply-To: <20220331084151.2600229-1-yosryahmed@google.com> From: Wei Xu Date: Thu, 31 Mar 2022 21:05:15 -0700 Message-ID: Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface To: Yosry Ahmed 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" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). > +} > + > 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 > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Xu Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface Date: Thu, 31 Mar 2022 21:05:15 -0700 Message-ID: References: <20220331084151.2600229-1-yosryahmed@google.com> Mime-Version: 1.0 Return-path: 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=B+CLss0WbItuifu72dHflWYaudPs9OpOIrtnBZ+LuaU=; b=W4lP36K+Sb0fsBGicZNNHA2PdXSFLxGLOGu+QIo0Pr+K09Bfb/JQ9y7h29SJTwHCkL qo9Meye8l/bh5ZdCafGJlboKfyAh3OTCZiwV615CLHt7foV27/crahdWIZpXP9o5zyDT f4B0knRfleCmNsT7S/1gVtK/jnuLe8dMnvgnkEw7P3BsrmJSWJR0z6u8myMWpvrwhycC K0MJjUxswzx2hsClKurU0lxBklqJnt5jCMfdXO/WkmQApUMQX+vefGDz6SReFNqKkDvo OLqXgs1GpET++yDSsieKbkumlNIePUfHJvkrEdI24CUoKeH4Ge+57mvK0e8QEpJiPpQ6 0WeQ== In-Reply-To: <20220331084151.2600229-1-yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Yosry Ahmed Cc: Johannes Weiner , Michal Hocko , Shakeel Butt , Andrew Morton , David Rientjes , Tejun Heo , Zefan Li , Roman Gushchin , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux Kernel Mailing List , Linux MM , Jonathan Corbet , Yu Zhao , Dave Hansen , Greg Thelen 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-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org/ > > 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-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org: 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). > +} > + > 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 >