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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 960DAC433E0 for ; Fri, 26 Feb 2021 01:17:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C97464F0D for ; Fri, 26 Feb 2021 01:17:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229894AbhBZBRU (ORCPT ); Thu, 25 Feb 2021 20:17:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:48524 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229769AbhBZBRI (ORCPT ); Thu, 25 Feb 2021 20:17:08 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 84BAA64F2B; Fri, 26 Feb 2021 01:16:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1614302208; bh=LpMLGDTMIAYZn24LxN4Rcm5txiBnIPh4BlB3AJIhZIk=; h=Date:From:To:Subject:In-Reply-To:From; b=1a0nafmLl6jYa5klihoR2V/K93oXedufhY0hAlWSDR/GYBiEvt1vuC5vJpQT6URBY aALw5/lVzYHSwrFAvrCptZ+Yl3zTkSWMKBN9p1s5FABbCiSFGeaBevQ2QETHsViJaw WTXTiALZt4uccwZFPsA4LRZcDRWmcp8HG314JXHw= Date: Thu, 25 Feb 2021 17:16:47 -0800 From: Andrew Morton To: akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 023/118] mm: vmstat: fix NOHZ wakeups for node stat changes Message-ID: <20210226011647.uVMjpRAVE%akpm@linux-foundation.org> In-Reply-To: <20210225171452.713967e96554bb6a53e44a19@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Johannes Weiner Subject: mm: vmstat: fix NOHZ wakeups for node stat changes On NOHZ, the periodic vmstat flushers on each CPU can go to sleep and won't wake up until stat changes are detected in the per-cpu deltas of the zone vmstat counters. In commit 75ef71840539 ("mm, vmstat: add infrastructure for per-node vmstats") per-node counters were introduced, and subsequently most stats were moved from the zone to the node level. However, the node counters weren't added to the NOHZ wakeup detection. In theory this can cause per-cpu errors to remain in the user-reported stats indefinitely. In practice this only affects a handful of sub counters (file_mapped, dirty and writeback e.g.) because other page state changes at the node level likely involve a change at the zone level as well (alloc and free, lru ops). Also, nobody has complained. Fix it up for completeness: wake up vmstat refreshing on node changes. Also remove the BUILD_BUG_ONs that assert counter size; we haven't relied on it since we added sizeof() to the range calculation in commit 13c9aaf7fa01 ("mm/vmstat.c: fix NUMA statistics updates"). Link: https://lkml.kernel.org/r/20210202184342.118513-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Signed-off-by: Andrew Morton --- mm/vmstat.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) --- a/mm/vmstat.c~mm-vmstat-fix-nohz-wakeups-for-node-stat-changes +++ a/mm/vmstat.c @@ -1894,16 +1894,12 @@ static void vmstat_update(struct work_st */ static bool need_update(int cpu) { + pg_data_t *last_pgdat = NULL; struct zone *zone; for_each_populated_zone(zone) { struct per_cpu_pageset *p = per_cpu_ptr(zone->pageset, cpu); - - BUILD_BUG_ON(sizeof(p->vm_stat_diff[0]) != 1); -#ifdef CONFIG_NUMA - BUILD_BUG_ON(sizeof(p->vm_numa_stat_diff[0]) != 2); -#endif - + struct per_cpu_nodestat *n; /* * The fast way of checking if there are any vmstat diffs. */ @@ -1915,6 +1911,13 @@ static bool need_update(int cpu) sizeof(p->vm_numa_stat_diff[0]))) return true; #endif + 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, NR_VM_NODE_STAT_ITEMS * + sizeof(n->vm_node_stat_diff[0]))) + return true; } return false; } _