From patchwork Fri Mar 4 18:40:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Shakeel Butt X-Patchwork-Id: 12769825 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 D8841C433F5 for ; Fri, 4 Mar 2022 18:40:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4B3FA8D0002; Fri, 4 Mar 2022 13:40:46 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4637B8D0001; Fri, 4 Mar 2022 13:40:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 32D078D0002; Fri, 4 Mar 2022 13:40:46 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 1E8B48D0001 for ; Fri, 4 Mar 2022 13:40:46 -0500 (EST) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id CF7889CD59 for ; Fri, 4 Mar 2022 18:40:45 +0000 (UTC) X-FDA: 79207570050.16.30388BB Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) by imf31.hostedemail.com (Postfix) with ESMTP id 6F8F62000D for ; Fri, 4 Mar 2022 18:40:45 +0000 (UTC) Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-2d6994a6942so77509097b3.17 for ; Fri, 04 Mar 2022 10:40:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=kcmyAeGkpK7r59rcNcxz8jTE3yUE+N3ayzd6XBblM0I=; b=mvLff3CoVSfT2aw6kcMrK88S909hTrrgtBVT9DD32PyLCwH95gcIWOBgv7d+B5Lk94 6hmjfyCbTACgGXuUxAuHbq2YdDtEgFXLlDJxgr16HWSidmhaQZ6/Gn0xcRhFCGj2H6To joT1GP1IfVR8Dsrm2glTVD3Xsj5i27miNaXmBqU2Azi8dzDhqV8o3qr/7mu6pH73YOfD iR8mjRPGmKQl8K5kVyArnaFqeOTwfccrAcc9Za6ETbCJER3RiaXUWmRkYm/aKORgLWsh 7uBH2hMZTq4emcVx+Hfi9V3Yfk9hJdS9TbVc4g33OkzABHo84zPYWIo6YrfcDWw/wA7/ lX6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=kcmyAeGkpK7r59rcNcxz8jTE3yUE+N3ayzd6XBblM0I=; b=VM7J3Xpvt/WgWhU7PUg3blNs+CVHl6FmBevmcAVd1SwTOaqEFOZQNnxDCyzCajSPsk SBwVGOb5oSROmJxhTJKbaWj982A1QIqAtofvfDZV16SGxg/PniQWHW35aO1Yn6vEdf5K U5lf+xlvchugBSy50zT/u85vqPAomIpEUIrKU+06oPV4m1rI6itxelCpz/ztmXeNQmlw yUAdMGrCMo/6JEjNEP8H5Z3DR5+SeZ04PKjv6liHEhWZI9EMBDgCrh7cm/szLSb43iTj SZGAtvmBbpOgIj45HCkE5ed/bKHu2jj6DZJMbDJsStBz2aVo5ccyQ0lgrkWjlMIq9STm P1FQ== X-Gm-Message-State: AOAM532G49hop93qkM1SdafMozCo2LYsjPTGO+R7MTj4LMs17cl3Gv6E +5OqM7m3NoZS1AI9JYXmHdrq895QA5WTgg== X-Google-Smtp-Source: ABdhPJxQbsi8RSzb6NYSX+gqf9JicHEI9Ols5mWOZ9t2xvgAme8I6b6RNy28Q54iJFfl4DPUNTHiNJ/cEzgcew== X-Received: from shakeelb.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:28b]) (user=shakeelb job=sendgmr) by 2002:a81:2450:0:b0:2d6:aee8:f0d5 with SMTP id k77-20020a812450000000b002d6aee8f0d5mr43748864ywk.81.1646419244705; Fri, 04 Mar 2022 10:40:44 -0800 (PST) Date: Fri, 4 Mar 2022 18:40:40 +0000 Message-Id: <20220304184040.1304781-1-shakeelb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.35.1.616.g0bdcbb4464-goog Subject: [PATCH] memcg: sync flush only if periodic flush is delayed From: Shakeel Butt To: " =?utf-8?q?Michal_Koutn=C3=BD?= " , Johannes Weiner , Michal Hocko , Roman Gushchin Cc: Ivan Babrou , Frank Hofmann , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt , Daniel Dao , stable@vger.kernel.org X-Rspamd-Queue-Id: 6F8F62000D X-Stat-Signature: 8bw813ubchk7nhqps3phu6eq7ofxc4kw Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=mvLff3Co; spf=pass (imf31.hostedemail.com: domain of 3LF0iYggKCIc3slvppwmrzzrwp.nzxwty58-xxv6lnv.z2r@flex--shakeelb.bounces.google.com designates 209.85.128.201 as permitted sender) smtp.mailfrom=3LF0iYggKCIc3slvppwmrzzrwp.nzxwty58-xxv6lnv.z2r@flex--shakeelb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1646419245-477398 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: Daniel Dao has reported [1] a regression on workloads that may trigger a lot of refaults (anon and file). The underlying issue is that flushing rstat is expensive. Although rstat flush are batched with (nr_cpus * MEMCG_BATCH) stat updates, it seems like there are workloads which genuinely do stat updates larger than batch value within short amount of time. Since the rstat flush can happen in the performance critical codepaths like page faults, such workload can suffer greatly. This patch fixes this regression by making the rstat flushing conditional in the performance critical codepaths. More specifically, the kernel relies on the async periodic rstat flusher to flush the stats and only if the periodic flusher is delayed by more than twice the amount of its normal time window then the kernel allows rstat flushing from the performance critical codepaths. Now the question: what are the side-effects of this change? The worst that can happen is the refault codepath will see 4sec old lruvec stats and may cause false (or missed) activations of the refaulted page which may under-or-overestimate the workingset size. Though that is not very concerning as the kernel can already miss or do false activations. There are two more codepaths whose flushing behavior is not changed by this patch and we may need to come to them in future. One is the writeback stats used by dirty throttling and second is the deactivation heuristic in the reclaim. For now keeping an eye on them and if there is report of regression due to these codepaths, we will reevaluate then. Link: https://lore.kernel.org/all/CA+wXwBSyO87ZX5PVwdHm-=dBjZYECGmfnydUicUyrQqndgX2MQ@mail.gmail.com [1] Fixes: 1f828223b799 ("memcg: flush lruvec stats in the refault") Signed-off-by: Shakeel Butt Reported-by: Daniel Dao Cc: Tested-by: Ivan Babrou --- include/linux/memcontrol.h | 5 +++++ mm/memcontrol.c | 12 +++++++++++- mm/workingset.c | 2 +- 3 files changed, 17 insertions(+), 2 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index a68dce3873fc..89b14729d59f 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1012,6 +1012,7 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec, } void mem_cgroup_flush_stats(void); +void mem_cgroup_flush_stats_delayed(void); void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val); @@ -1455,6 +1456,10 @@ static inline void mem_cgroup_flush_stats(void) { } +static inline void mem_cgroup_flush_stats_delayed(void) +{ +} + static inline void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f79bb3f25ce4..edfb337e6948 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -587,6 +587,9 @@ static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork); static DEFINE_SPINLOCK(stats_flush_lock); static DEFINE_PER_CPU(unsigned int, stats_updates); static atomic_t stats_flush_threshold = ATOMIC_INIT(0); +static u64 flush_next_time; + +#define FLUSH_TIME (2UL*HZ) /* * Accessors to ensure that preemption is disabled on PREEMPT_RT because it can @@ -637,6 +640,7 @@ static void __mem_cgroup_flush_stats(void) if (!spin_trylock_irqsave(&stats_flush_lock, flag)) return; + flush_next_time = jiffies_64 + 2*FLUSH_TIME; cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup); atomic_set(&stats_flush_threshold, 0); spin_unlock_irqrestore(&stats_flush_lock, flag); @@ -648,10 +652,16 @@ void mem_cgroup_flush_stats(void) __mem_cgroup_flush_stats(); } +void mem_cgroup_flush_stats_delayed(void) +{ + if (rstat_flush_time && time_after64(jiffies_64, flush_next_time)) + mem_cgroup_flush_stats(); +} + static void flush_memcg_stats_dwork(struct work_struct *w) { __mem_cgroup_flush_stats(); - queue_delayed_work(system_unbound_wq, &stats_flush_dwork, 2UL*HZ); + queue_delayed_work(system_unbound_wq, &stats_flush_dwork, FLUSH_TIME); } /** diff --git a/mm/workingset.c b/mm/workingset.c index 8a3828acc0bf..592569a8974c 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -355,7 +355,7 @@ void workingset_refault(struct folio *folio, void *shadow) mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr); - mem_cgroup_flush_stats(); + mem_cgroup_flush_stats_delayed(); /* * Compare the distance to the existing workingset size. We * don't activate pages that couldn't stay resident even if