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 9492CC74A4B for ; Mon, 13 Mar 2023 18:08:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229826AbjCMSH7 (ORCPT ); Mon, 13 Mar 2023 14:07:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230305AbjCMSHz (ORCPT ); Mon, 13 Mar 2023 14:07:55 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 604E679B13 for ; Mon, 13 Mar 2023 11:07:46 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 0AD88B811C9 for ; Mon, 13 Mar 2023 18:07:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 928D8C433D2; Mon, 13 Mar 2023 18:07:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1678730863; bh=UgtP7RH1jm95rCKcL/cx90jNDvD8YxvHg2CfAQQVolU=; h=Date:To:From:Subject:From; b=D2MYt2+rHqZrUlh3POp0aAN5tCE3sRH5eQI7bgjOc3Gz+8hPtYp7SNafzDt0Y18AT e2igeNkh+M7kgL1dVL4SFG2FhqL8NEjw2IPg4uGah2GYzgkv5a4tdPojukJC6sRuA2 GLxoOwMJWT2U719mFEruOqufFShpiem/TnQ6NGps= Date: Mon, 13 Mar 2023 11:07:43 -0700 To: mm-commits@vger.kernel.org, willy@infradead.org, vbabka@suse.cz, thomas.hellstrom@linux.intel.com, peterx@redhat.com, mhocko@suse.com, lstoakes@gmail.com, linux@armlinux.org.uk, kirill.shutemov@linux.intel.com, jgg@ziepe.ca, hca@linux.ibm.com, frederic@kernel.org, dan.j.williams@intel.com, cl@linux.com, christian.koenig@amd.com, chenhuacai@kernel.org, atomlin@atomlin.com, mtosatti@redhat.com, akpm@linux-foundation.org From: Andrew Morton Subject: + mm-vmstat-switch-vmstat-shepherd-to-flush-per-cpu-counters-remotely.patch added to mm-unstable branch Message-Id: <20230313180743.928D8C433D2@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: mm/vmstat: switch vmstat shepherd to flush per-CPU counters remotely has been added to the -mm mm-unstable branch. Its filename is mm-vmstat-switch-vmstat-shepherd-to-flush-per-cpu-counters-remotely.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmstat-switch-vmstat-shepherd-to-flush-per-cpu-counters-remotely.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Marcelo Tosatti Subject: mm/vmstat: switch vmstat shepherd to flush per-CPU counters remotely Date: Mon, 13 Mar 2023 13:25:17 -0300 Now that the counters are modified via cmpxchg both CPU locally (via the account functions), and remotely (via cpu_vm_stats_fold), its possible to switch vmstat_shepherd to perform the per-CPU vmstats folding remotely. This fixes the following two problems: 1. 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()) 2. With a SCHED_FIFO task that busy loops on a given CPU, and kworker for that CPU at SCHED_OTHER priority, queuing work to sync per-vmstats will either cause that work to never execute, or stalld (i.e. stall daemon) boosts kworker priority which causes a latency violation Link: https://lkml.kernel.org/r/20230313162634.509267576@redhat.com Signed-off-by: Marcelo Tosatti Cc: Aaron Tomlin Cc: Christian König Cc: Christoph Lameter Cc: Dan Williams Cc: Frederic Weisbecker Cc: Heiko Carstens Cc: Huacai Chen Cc: Jason Gunthorpe Cc: Kirill A. Shutemov Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Peter Xu Cc: "Russell King (Oracle)" Cc: Thomas Hellström Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- --- a/mm/vmstat.c~mm-vmstat-switch-vmstat-shepherd-to-flush-per-cpu-counters-remotely +++ a/mm/vmstat.c @@ -2049,6 +2049,23 @@ static void vmstat_shepherd(struct work_ static DECLARE_DEFERRABLE_WORK(shepherd, vmstat_shepherd); +#ifdef CONFIG_HAVE_CMPXCHG_LOCAL +/* Flush counters remotely if CPU uses cmpxchg to update its per-CPU counters */ +static void vmstat_shepherd(struct work_struct *w) +{ + int cpu; + + cpus_read_lock(); + for_each_online_cpu(cpu) { + cpu_vm_stats_fold(cpu); + cond_resched(); + } + cpus_read_unlock(); + + schedule_delayed_work(&shepherd, + round_jiffies_relative(sysctl_stat_interval)); +} +#else static void vmstat_shepherd(struct work_struct *w) { int cpu; @@ -2068,6 +2085,7 @@ static void vmstat_shepherd(struct work_ schedule_delayed_work(&shepherd, round_jiffies_relative(sysctl_stat_interval)); } +#endif static void __init start_shepherd_timer(void) { _ Patches currently in -mm which might be from mtosatti@redhat.com are this_cpu_cmpxchg-arm64-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch this_cpu_cmpxchg-loongarch-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch this_cpu_cmpxchg-s390-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch this_cpu_cmpxchg-x86-switch-this_cpu_cmpxchg-to-locked-add-_local-function.patch add-this_cpu_cmpxchg_local-and-asm-generic-definitions.patch convert-this_cpu_cmpxchg-users-to-this_cpu_cmpxchg_local.patch mm-vmstat-switch-counter-modification-to-cmpxchg.patch vmstat-switch-per-cpu-vmstat-counters-to-32-bits.patch mm-vmstat-use-xchg-in-cpu_vm_stats_fold.patch mm-vmstat-switch-vmstat-shepherd-to-flush-per-cpu-counters-remotely.patch mm-vmstat-refresh-stats-remotely-instead-of-via-work-item.patch vmstat-add-pcp-remote-node-draining-via-cpu_vm_stats_fold.patch