From patchwork Fri Nov 5 20:37:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12605473 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BED80C433EF for ; Fri, 5 Nov 2021 20:37:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 734E461242 for ; Fri, 5 Nov 2021 20:37:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 734E461242 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 107A2940033; Fri, 5 Nov 2021 16:37:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 09080940034; Fri, 5 Nov 2021 16:37:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DFC5D940033; Fri, 5 Nov 2021 16:37:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0116.hostedemail.com [216.40.44.116]) by kanga.kvack.org (Postfix) with ESMTP id C951A940007 for ; Fri, 5 Nov 2021 16:37:33 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 8B8561856A8FE for ; Fri, 5 Nov 2021 20:37:33 +0000 (UTC) X-FDA: 78776037312.05.04F7BD1 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf28.hostedemail.com (Postfix) with ESMTP id 27A7A90000AD for ; Fri, 5 Nov 2021 20:37:33 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 1FCC66056B; Fri, 5 Nov 2021 20:37:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1636144652; bh=sbSbvXulVG76Pdn5K0qar18qXE+PpMEkpUnJ5PUvKEs=; h=Date:From:To:Subject:In-Reply-To:From; b=UyOKve9TzyKbcNUVOz5tUwWrg5OAtOfUrq1WEHZ/xMbonwK95eQQuHgQHjNfRMnH5 epM/UrSuKdW5NOei3ia6/vqy5/LpXQYun47zGnRndJ+qHVnkPfeLeRjxiAy+jiVStL mU3mOTBJmoVfaoE7hlIC0JDxoYOI+1hJpJ92C8a0= Date: Fri, 05 Nov 2021 13:37:31 -0700 From: Andrew Morton To: akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@kernel.org, mkoutny@suse.com, mm-commits@vger.kernel.org, shakeelb@google.com, torvalds@linux-foundation.org Subject: [patch 055/262] memcg: flush stats only if updated Message-ID: <20211105203731.uHUWGR8SE%akpm@linux-foundation.org> In-Reply-To: <20211105133408.cccbb98b71a77d5e8430aba1@linux-foundation.org> User-Agent: s-nail v14.8.16 MIME-Version: 1.0 Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=UyOKve9T; dmarc=none; spf=pass (imf28.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 27A7A90000AD X-Stat-Signature: diqjbziepdggif5bsfkqnoya4s17brr6 X-HE-Tag: 1636144653-437636 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: From: Shakeel Butt Subject: memcg: flush stats only if updated At the moment, the kernel flushes the memcg stats on every refault and also on every reclaim iteration. Although rstat maintains per-cpu update tree but on the flush the kernel still has to go through all the cpu rstat update tree to check if there is anything to flush. This patch adds the tracking on the stats update side to make flush side more clever by skipping the flush if there is no update. The stats update codepath is very sensitive performance wise for many workloads and benchmarks. So, we can not follow what the commit aa48e47e3906 ("memcg: infrastructure to flush memcg stats") did which was triggering async flush through queue_work() and caused a lot performance regression reports. That got reverted by the commit 1f828223b799 ("memcg: flush lruvec stats in the refault"). In this patch we kept the stats update codepath very minimal and let the stats reader side to flush the stats only when the updates are over a specific threshold. For now the threshold is (nr_cpus * CHARGE_BATCH). To evaluate the impact of this patch, an 8 GiB tmpfs file is created on a system with swap-on-zram and the file was pushed to swap through memory.force_empty interface. On reading the whole file, the memcg stat flush in the refault code path is triggered. With this patch, we observed 63% reduction in the read time of 8 GiB file. Link: https://lkml.kernel.org/r/20211001190040.48086-1-shakeelb@google.com Signed-off-by: Shakeel Butt Acked-by: Johannes Weiner Cc: Michal Hocko Reviewed-by: "Michal Koutný" Signed-off-by: Andrew Morton --- mm/memcontrol.c | 78 ++++++++++++++++++++++++++++++++-------------- 1 file changed, 55 insertions(+), 23 deletions(-) --- a/mm/memcontrol.c~memcg-flush-stats-only-if-updated +++ a/mm/memcontrol.c @@ -103,11 +103,6 @@ static bool do_memsw_account(void) return !cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_noswap; } -/* memcg and lruvec stats flushing */ -static void flush_memcg_stats_dwork(struct work_struct *w); -static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork); -static DEFINE_SPINLOCK(stats_flush_lock); - #define THRESHOLDS_EVENTS_TARGET 128 #define SOFTLIMIT_EVENTS_TARGET 1024 @@ -635,6 +630,56 @@ mem_cgroup_largest_soft_limit_node(struc return mz; } +/* + * memcg and lruvec stats flushing + * + * Many codepaths leading to stats update or read are performance sensitive and + * adding stats flushing in such codepaths is not desirable. So, to optimize the + * flushing the kernel does: + * + * 1) Periodically and asynchronously flush the stats every 2 seconds to not let + * rstat update tree grow unbounded. + * + * 2) Flush the stats synchronously on reader side only when there are more than + * (MEMCG_CHARGE_BATCH * nr_cpus) update events. Though this optimization + * will let stats be out of sync by atmost (MEMCG_CHARGE_BATCH * nr_cpus) but + * only for 2 seconds due to (1). + */ +static void flush_memcg_stats_dwork(struct work_struct *w); +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 inline void memcg_rstat_updated(struct mem_cgroup *memcg) +{ + cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id()); + if (!(__this_cpu_inc_return(stats_updates) % MEMCG_CHARGE_BATCH)) + atomic_inc(&stats_flush_threshold); +} + +static void __mem_cgroup_flush_stats(void) +{ + if (!spin_trylock(&stats_flush_lock)) + return; + + cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup); + atomic_set(&stats_flush_threshold, 0); + spin_unlock(&stats_flush_lock); +} + +void mem_cgroup_flush_stats(void) +{ + if (atomic_read(&stats_flush_threshold) > num_online_cpus()) + __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); +} + /** * __mod_memcg_state - update cgroup memory statistics * @memcg: the memory cgroup @@ -647,7 +692,7 @@ void __mod_memcg_state(struct mem_cgroup return; __this_cpu_add(memcg->vmstats_percpu->state[idx], val); - cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id()); + memcg_rstat_updated(memcg); } /* idx can be of type enum memcg_stat_item or node_stat_item. */ @@ -675,10 +720,12 @@ void __mod_memcg_lruvec_state(struct lru memcg = pn->memcg; /* Update memcg */ - __mod_memcg_state(memcg, idx, val); + __this_cpu_add(memcg->vmstats_percpu->state[idx], val); /* Update lruvec */ __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); + + memcg_rstat_updated(memcg); } /** @@ -780,7 +827,7 @@ void __count_memcg_events(struct mem_cgr return; __this_cpu_add(memcg->vmstats_percpu->events[idx], count); - cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id()); + memcg_rstat_updated(memcg); } static unsigned long memcg_events(struct mem_cgroup *memcg, int event) @@ -5341,21 +5388,6 @@ static void mem_cgroup_css_reset(struct memcg_wb_domain_size_changed(memcg); } -void mem_cgroup_flush_stats(void) -{ - if (!spin_trylock(&stats_flush_lock)) - return; - - cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup); - spin_unlock(&stats_flush_lock); -} - -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); -} - static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu) { struct mem_cgroup *memcg = mem_cgroup_from_css(css);