From patchwork Mon Aug 8 19:48:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Aaron Tomlin X-Patchwork-Id: 12939099 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 4C7F7C00140 for ; Mon, 8 Aug 2022 19:48:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CEC5B6B0073; Mon, 8 Aug 2022 15:48:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C75278E0002; Mon, 8 Aug 2022 15:48:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AEE728E0001; Mon, 8 Aug 2022 15:48:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 9D47D6B0073 for ; Mon, 8 Aug 2022 15:48:28 -0400 (EDT) Received: from smtpin31.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 79B56A5852 for ; Mon, 8 Aug 2022 19:48:28 +0000 (UTC) X-FDA: 79777462296.31.5448B58 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf19.hostedemail.com (Postfix) with ESMTP id 0C2041A013B for ; Mon, 8 Aug 2022 19:48:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659988107; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IEGgPc6kXu5gJq3u5V+y6qTg7ywEaMnnfFNE/DMiRTs=; b=GQK54kTZLdpofVv5tshqqFJtI1NMMTBjJ13m9nwa1iSIeaR/51RoOkbCkAtpSEwkgd1+VZ upMiLjGVsnORxjYbIGo006urdBiAfxi97IkPfxNW0uAZTOyBTxuLAcGL4DNq+8E7k38WjU Pwx3UJx1Qv4Hm8dfQL+Z+XL1ReJEj9U= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-515-wEnHlUBDNH6mJ6rmEgML8Q-1; Mon, 08 Aug 2022 15:48:26 -0400 X-MC-Unique: wEnHlUBDNH6mJ6rmEgML8Q-1 Received: by mail-wr1-f69.google.com with SMTP id x5-20020adfbb45000000b0021ee56506dfso1635339wrg.11 for ; Mon, 08 Aug 2022 12:48:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=IEGgPc6kXu5gJq3u5V+y6qTg7ywEaMnnfFNE/DMiRTs=; b=K5tQIQ/TFlQG7ENXVSWxLgCEIIZT7NgOMhFUO2xXl6xUiyOQzq+Efp7Q8Gy5p3Vi+w WpOHZt7dMZ3y2H8c2FHDi7C28U7WVpKt91Tt/yCAF8rd1yS5+6p+g7tH/JeQUBukqHmE aAKiI0mJCuFUejA8by+747HWT9kkpOhRGOLtnW3wOO1eqiOkmnuAxDklH/+nRvByYWvr 0+CFSvVib8xpuuk5RqOc4zs3CmBjf9rGHwRk9NETLwh60l+29s4uQcKFdEAnQkKPjSEr NHnksV2MakmoF2RsENM0RfuMPMQoRa9qj8I+VaMaGX/5lxclGYYRBgTw6BelU9Pq9cLZ jTgQ== X-Gm-Message-State: ACgBeo1REeP5nCCqfgAxk9Pr0LsFSGiF8Kgy7bWjCWougNASI1lZ0ZGI EDmHUzADOdCFsU+BJJVov9DbJEVq0EDArQ0oYJsU03561jlBfTBSTrWM7AzfdOoIDgAfP1YKEWX DnK9HHf+VLA== X-Received: by 2002:a05:6000:a13:b0:220:62e6:5f79 with SMTP id co19-20020a0560000a1300b0022062e65f79mr12348670wrb.45.1659988105663; Mon, 08 Aug 2022 12:48:25 -0700 (PDT) X-Google-Smtp-Source: AA6agR4Db4VKdX6HbbVZxJFXbXkTzkfDbMXt99KIC4g2B5bXybiUQFPjoT64TLqnJf38iLorwCfxAA== X-Received: by 2002:a05:6000:a13:b0:220:62e6:5f79 with SMTP id co19-20020a0560000a1300b0022062e65f79mr12348652wrb.45.1659988105429; Mon, 08 Aug 2022 12:48:25 -0700 (PDT) Received: from localhost (cpc111743-lutn13-2-0-cust979.9-3.cable.virginm.net. [82.17.115.212]) by smtp.gmail.com with ESMTPSA id g17-20020a5d5551000000b0021e4f595590sm12076081wrw.28.2022.08.08.12.48.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Aug 2022 12:48:24 -0700 (PDT) From: Aaron Tomlin To: frederic@kernel.org, mtosatti@redhat.com Cc: cl@linux.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, atomlin@atomlin.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v6 1/2] mm/vmstat: Use per cpu variable to track a vmstat discrepancy Date: Mon, 8 Aug 2022 20:48:19 +0100 Message-Id: <20220808194820.676246-2-atomlin@redhat.com> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220808194820.676246-1-atomlin@redhat.com> References: <20220808194820.676246-1-atomlin@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1659988108; a=rsa-sha256; cv=none; b=RCOhLcuxUD0Q/a4DKr6tOufbBAnt2instptQwmBHH1NndFf9FCHzmDL8Ck8Ybc877Zj/+N DDgScYUKza+s6lO3WEwHKGSvTPMTlZuRz3OZojG8CiudI2iRg/9KgOw7pCTZakCeDVCw7J wr2Mi6tWsFqhmQoAx18urU9P6leYDwQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659988108; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=IEGgPc6kXu5gJq3u5V+y6qTg7ywEaMnnfFNE/DMiRTs=; b=vK63oAy+rEMsndnocMNTeyvY46xER5c7/DRZQgf9gnHiDLo1IZCjDq4Dtcn4OgqRgICCnY mMnspkqm7l8Zi106kH44p5Mj7x/42i/vnUjj9GXC40iw77kHbiVFwuJE1qXP5vIR4lZoo1 Spf3wD+GRyM685/01dAVz0tGyBFtqQk= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=GQK54kTZ; spf=pass (imf19.hostedemail.com: domain of atomlin@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: xcy1c3qaq7onyok6ujckxhrrcom4jkes X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0C2041A013B Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=GQK54kTZ; spf=pass (imf19.hostedemail.com: domain of atomlin@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1659988107-912163 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: This patch incorporates an idea from Marcelo's patch [1] where a CPU-specific variable namely vmstat_dirty is used to indicate if a vmstat imbalance is present for a given CPU. Therefore, at the appropriate time, we can fold all the remaining differentials. [1]: https://lore.kernel.org/lkml/20220204173554.763888172@fedora.localdomain/ Signed-off-by: Aaron Tomlin --- mm/vmstat.c | 46 +++++++++++++++------------------------------- 1 file changed, 15 insertions(+), 31 deletions(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index 373d2730fcf2..51564b7c85fe 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -195,6 +195,12 @@ void fold_vm_numa_events(void) #endif #ifdef CONFIG_SMP +static DEFINE_PER_CPU_ALIGNED(bool, vmstat_dirty); + +static inline void mark_vmstat_dirty(void) +{ + this_cpu_write(vmstat_dirty, true); +} int calculate_pressure_threshold(struct zone *zone) { @@ -367,6 +373,7 @@ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item, x = 0; } __this_cpu_write(*p, x); + mark_vmstat_dirty(); if (IS_ENABLED(CONFIG_PREEMPT_RT)) preempt_enable(); @@ -405,6 +412,7 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, x = 0; } __this_cpu_write(*p, x); + mark_vmstat_dirty(); if (IS_ENABLED(CONFIG_PREEMPT_RT)) preempt_enable(); @@ -603,6 +611,7 @@ static inline void mod_zone_state(struct zone *zone, if (z) zone_page_state_add(z, zone, item); + mark_vmstat_dirty(); } void mod_zone_page_state(struct zone *zone, enum zone_stat_item item, @@ -671,6 +680,7 @@ static inline void mod_node_state(struct pglist_data *pgdat, if (z) node_page_state_add(z, pgdat, item); + mark_vmstat_dirty(); } void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, @@ -1873,6 +1883,7 @@ int sysctl_stat_interval __read_mostly = HZ; static void refresh_vm_stats(struct work_struct *work) { refresh_cpu_vm_stats(true); + this_cpu_write(vmstat_dirty, false); } int vmstat_refresh(struct ctl_table *table, int write, @@ -1937,6 +1948,7 @@ int vmstat_refresh(struct ctl_table *table, int write, static void vmstat_update(struct work_struct *w) { if (refresh_cpu_vm_stats(true)) { + this_cpu_write(vmstat_dirty, false); /* * Counters were updated so we expect more updates * to occur in the future. Keep on running the @@ -1948,35 +1960,6 @@ static void vmstat_update(struct work_struct *w) } } -/* - * Check if the diffs for a certain cpu indicate that - * an update is needed. - */ -static bool need_update(int cpu) -{ - pg_data_t *last_pgdat = NULL; - struct zone *zone; - - for_each_populated_zone(zone) { - struct per_cpu_zonestat *pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu); - struct per_cpu_nodestat *n; - - /* - * The fast way of checking if there are any vmstat diffs. - */ - if (memchr_inv(pzstats->vm_stat_diff, 0, sizeof(pzstats->vm_stat_diff))) - return true; - - if (last_pgdat == zone->zone_pgdat) - continue; - last_pgdat = zone->zone_pgdat; - n = per_cpu_ptr(zone->zone_pgdat->per_cpu_nodestats, cpu); - if (memchr_inv(n->vm_node_stat_diff, 0, sizeof(n->vm_node_stat_diff))) - return true; - } - return false; -} - /* * Switch off vmstat processing and then fold all the remaining differentials * until the diffs stay at zero. The function is used by NOHZ and can only be @@ -1990,7 +1973,7 @@ void quiet_vmstat(void) if (!delayed_work_pending(this_cpu_ptr(&vmstat_work))) return; - if (!need_update(smp_processor_id())) + if (!__this_cpu_read(vmstat_dirty)) return; /* @@ -2000,6 +1983,7 @@ void quiet_vmstat(void) * vmstat_shepherd will take care about that for us. */ refresh_cpu_vm_stats(false); + __this_cpu_write(vmstat_dirty, false); } /* @@ -2021,7 +2005,7 @@ static void vmstat_shepherd(struct work_struct *w) for_each_online_cpu(cpu) { struct delayed_work *dw = &per_cpu(vmstat_work, cpu); - if (!delayed_work_pending(dw) && need_update(cpu)) + if (!delayed_work_pending(dw) && per_cpu(vmstat_dirty, cpu)) queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0); cond_resched(); From patchwork Mon Aug 8 19:48:20 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Aaron Tomlin X-Patchwork-Id: 12939100 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 ACFB7C00140 for ; Mon, 8 Aug 2022 19:48:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4B0066B0074; Mon, 8 Aug 2022 15:48:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 437868E0002; Mon, 8 Aug 2022 15:48:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 28A658E0001; Mon, 8 Aug 2022 15:48:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 17AC96B0074 for ; Mon, 8 Aug 2022 15:48:34 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id E40F81C5C61 for ; Mon, 8 Aug 2022 19:48:33 +0000 (UTC) X-FDA: 79777462506.24.82CB5A2 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf26.hostedemail.com (Postfix) with ESMTP id 8037E14002C for ; Mon, 8 Aug 2022 19:48:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659988113; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JIOXcCqOziO3sWReC1tPOoazvhM86qdX3oRCW3muMkA=; b=N3F17PhO8VykEdHDfnAV5g+ju8ttKFrU+KE/T8OYy7Ux0Q6jFNIWNy5P//2Xf4BHTeSPOl MXnY4cOep6UB5lZre3eZftHG6skRl2CT9fKadax/SONXK+yObcbFNnH99Ba2sdZhgInAwS 90LRqEG1PzmyBj5OGv99y8aaINbhyfc= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-630-IPP9-LxYMcKwRLc7WY69BQ-1; Mon, 08 Aug 2022 15:48:29 -0400 X-MC-Unique: IPP9-LxYMcKwRLc7WY69BQ-1 Received: by mail-wm1-f69.google.com with SMTP id n19-20020a05600c3b9300b003a314062cf4so8889wms.0 for ; Mon, 08 Aug 2022 12:48:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=JIOXcCqOziO3sWReC1tPOoazvhM86qdX3oRCW3muMkA=; b=39do7u4bFR2pfG/1SAstGN23ubbsNzRpQ1bUPbZmxTSWIAasmVbSplw9yTGPKR9XhG CMmymTCHH/i+qm8lpyRdKpqPIvIqgecsvowLWpA6fnk60MlIyiYxx8hESABjPsJP/qT0 ouVjPGEbcLgMMbbuIxvUsv9RGDVC4OY6vzbuYcxaxNiqJt/YAeAmQZD2TcLkw2f21xT/ aoL027sYcHb5g+XLSisO+hYptG0pBnIGmSa5685L65J95C0s2eXjIvn9YzmctYMrS8Im lOk679Fa4JX2aGQdb8a1VM5yjCIXt30MhEjQfcdYlnRLmeJcQS47zNuv3sKn1TEZFIq+ fjIQ== X-Gm-Message-State: ACgBeo3Qqi6jjzlXxhkNtyt0aTLyLpklkouIpL/DDqgXvF6egj5mZYo/ hLUC+Kbp593eX15xdaYZe5tIeZMQm0pJVm53kZk4F8iVoW19ipnzcXLfmiYSx7Tj0kye6cDspDB NBZOa42alWA== X-Received: by 2002:a05:600c:3d06:b0:3a3:58f6:9d96 with SMTP id bh6-20020a05600c3d0600b003a358f69d96mr18350220wmb.195.1659988108549; Mon, 08 Aug 2022 12:48:28 -0700 (PDT) X-Google-Smtp-Source: AA6agR4fD3/gWNHA5NwUp6wkXU6HzBnT8FofIoL4dDf71R+cTCGZmCS0PxtbaUkEtWaw9eKFE2nX/A== X-Received: by 2002:a05:600c:3d06:b0:3a3:58f6:9d96 with SMTP id bh6-20020a05600c3d0600b003a358f69d96mr18350198wmb.195.1659988108242; Mon, 08 Aug 2022 12:48:28 -0700 (PDT) Received: from localhost (cpc111743-lutn13-2-0-cust979.9-3.cable.virginm.net. [82.17.115.212]) by smtp.gmail.com with ESMTPSA id l2-20020a1ced02000000b003a3170a7af9sm14218192wmh.4.2022.08.08.12.48.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Aug 2022 12:48:26 -0700 (PDT) From: Aaron Tomlin To: frederic@kernel.org, mtosatti@redhat.com Cc: cl@linux.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, atomlin@atomlin.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v6 2/2] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Date: Mon, 8 Aug 2022 20:48:20 +0100 Message-Id: <20220808194820.676246-3-atomlin@redhat.com> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220808194820.676246-1-atomlin@redhat.com> References: <20220808194820.676246-1-atomlin@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1659988113; a=rsa-sha256; cv=none; b=zJ3pijFler2Uis54f6BIKs7wkquFhie/b6pIBkaNIGm1n8gHD/gW00R3ujqabuTFB8Fz6G PPZ3TcvQcmkgYnTTVcgKgjtaeEDhxGXfyO7dTN8g11sK/Lm45oL8afpAj8F0EMp4BWowQF xgB8Dlr0nIDFnDhAnPZA6iP0yBFX3ug= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=N3F17PhO; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf26.hostedemail.com: domain of atomlin@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659988113; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=JIOXcCqOziO3sWReC1tPOoazvhM86qdX3oRCW3muMkA=; b=koxgTK07i6MKYynJNtacWBKf/eZBnWY2HCbtrGl33x6c8+BXdIbqH040GzkNOb/kUX1Hlu 8Cm6K4fs7nc7Sr/SPhH0N/rf8TqvCFTU1sAphSERKk0jTmmLqBBiI2ZR3Xa/xFkCwZmi1v 0DSoQ/eW6JkKZdVA1D18YeqKCr/HK3Q= X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8037E14002C Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=N3F17PhO; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf26.hostedemail.com: domain of atomlin@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com X-Rspam-User: X-Stat-Signature: q969f5uocie6kq1tx1ej1mik9e7emybn X-HE-Tag: 1659988113-967439 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: In the context of the idle task and an adaptive-tick mode/or a nohz_full CPU, quiet_vmstat() can be called: before stopping the idle tick, entering an idle state and on exit. In particular, for the latter case, when the idle task is required to reschedule, the idle tick can remain stopped and the timer expiration time endless i.e., KTIME_MAX. Now, indeed before a nohz_full CPU enters an idle state, CPU-specific vmstat counters should be processed to ensure the respective values have been reset and folded into the zone specific 'vm_stat[]'. That being said, it can only occur when: the idle tick was previously stopped, and reprogramming of the timer is not required. A customer provided some evidence which indicates that the idle tick was stopped; albeit, CPU-specific vmstat counters still remained populated. Thus one can only assume quiet_vmstat() was not invoked on return to the idle loop. If I understand correctly, I suspect this divergence might erroneously prevent a reclaim attempt by kswapd. If the number of zone specific free pages are below their per-cpu drift value then zone_page_state_snapshot() is used to compute a more accurate view of the aforementioned statistic. Thus any task blocked on the NUMA node specific pfmemalloc_wait queue will be unable to make significant progress via direct reclaim unless it is killed after being woken up by kswapd (see throttle_direct_reclaim()). Consider the following theoretical scenario: 1. CPU Y migrated running task A to CPU X that was in an idle state i.e. waiting for an IRQ - not polling; marked the current task on CPU X to need/or require a reschedule i.e., set TIF_NEED_RESCHED and invoked a reschedule IPI to CPU X (see sched_move_task()) 2. CPU X acknowledged the reschedule IPI from CPU Y; generic idle loop code noticed the TIF_NEED_RESCHED flag against the idle task and attempts to exit of the loop and calls the main scheduler function i.e. __schedule(). Since the idle tick was previously stopped no scheduling-clock tick would occur. So, no deferred timers would be handled 3. Post transition to kernel execution Task A running on CPU Y, indirectly released a few pages (e.g. see __free_one_page()); CPU Y's 'vm_stat_diff[NR_FREE_PAGES]' was updated and zone specific 'vm_stat[]' update was deferred as per the CPU-specific stat threshold 4. Task A does invoke exit(2) and the kernel does remove the task from the run-queue; the idle task was selected to execute next since there are no other runnable tasks assigned to the given CPU (see pick_next_task() and pick_next_task_idle()) 5. On return to the idle loop since the idle tick was already stopped and can remain so (see [1] below) e.g. no pending soft IRQs, no attempt is made to zero and fold CPU Y's vmstat counters since reprogramming of the scheduling-clock tick is not required/or needed (see [2]) ... do_idle { __current_set_polling() tick_nohz_idle_enter() while (!need_resched()) { local_irq_disable() ... /* No polling or broadcast event */ cpuidle_idle_call() { if (cpuidle_not_available(drv, dev)) { tick_nohz_idle_stop_tick() __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched)) { int cpu = smp_processor_id() if (ts->timer_expires_base) expires = ts->timer_expires else if (can_stop_idle_tick(cpu, ts)) (1) -------> expires = tick_nohz_next_event(ts, cpu) else return ts->idle_calls++ if (expires > 0LL) { tick_nohz_stop_tick(ts, cpu) { if (ts->tick_stopped && (expires == ts->next_tick)) { (2) -------> if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer)) return } ... } So the idea of with this patch is to ensure refresh_cpu_vm_stats(false) is called, when it is appropriate, on return to the idle loop when the idle tick was previously stopped too. Additionally, in the context of nohz_full, when the scheduling-tick is stopped and before exiting to user-mode, ensure no CPU-specific vmstat differentials remain. Signed-off-by: Aaron Tomlin --- include/linux/tick.h | 5 +++-- kernel/time/tick-sched.c | 19 ++++++++++++++++++- 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/include/linux/tick.h b/include/linux/tick.h index bfd571f18cfd..a2bbd6d32e33 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -11,7 +11,6 @@ #include #include #include -#include #ifdef CONFIG_GENERIC_CLOCKEVENTS extern void __init tick_init(void); @@ -272,6 +271,7 @@ static inline void tick_dep_clear_signal(struct signal_struct *signal, extern void tick_nohz_full_kick_cpu(int cpu); extern void __tick_nohz_task_switch(void); +void __tick_nohz_user_enter_prepare(void); extern void __init tick_nohz_full_setup(cpumask_var_t cpumask); #else static inline bool tick_nohz_full_enabled(void) { return false; } @@ -296,6 +296,7 @@ static inline void tick_dep_clear_signal(struct signal_struct *signal, static inline void tick_nohz_full_kick_cpu(int cpu) { } static inline void __tick_nohz_task_switch(void) { } +static inline void __tick_nohz_user_enter_prepare(void) { } static inline void tick_nohz_full_setup(cpumask_var_t cpumask) { } #endif @@ -308,7 +309,7 @@ static inline void tick_nohz_task_switch(void) static inline void tick_nohz_user_enter_prepare(void) { if (tick_nohz_full_cpu(smp_processor_id())) - rcu_nocb_flush_deferred_wakeup(); + __tick_nohz_user_enter_prepare(); } #endif diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 30049580cd62..7f75fc1bba46 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -26,6 +26,7 @@ #include #include #include +#include #include @@ -519,6 +520,20 @@ void __tick_nohz_task_switch(void) } } +void __tick_nohz_user_enter_prepare(void) +{ + struct tick_sched *ts; + + if (tick_nohz_full_cpu(smp_processor_id())) { + ts = this_cpu_ptr(&tick_cpu_sched); + + if (ts->tick_stopped) + quiet_vmstat(); + rcu_nocb_flush_deferred_wakeup(); + } +} +EXPORT_SYMBOL_GPL(__tick_nohz_user_enter_prepare); + /* Get the boot-time nohz CPU list from the kernel parameters. */ void __init tick_nohz_full_setup(cpumask_var_t cpumask) { @@ -890,6 +905,9 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) ts->do_timer_last = 0; } + /* Attempt to fold when the idle tick is stopped or not */ + quiet_vmstat(); + /* Skip reprogram of event if its not changed */ if (ts->tick_stopped && (expires == ts->next_tick)) { /* Sanity check: make sure clockevent is actually programmed */ @@ -911,7 +929,6 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) */ if (!ts->tick_stopped) { calc_load_nohz_start(); - quiet_vmstat(); ts->last_tick = hrtimer_get_expires(&ts->sched_timer); ts->tick_stopped = 1;