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 32953C678DB for ; Sun, 5 Mar 2023 13:42:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229820AbjCENmp (ORCPT ); Sun, 5 Mar 2023 08:42:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229785AbjCENme (ORCPT ); Sun, 5 Mar 2023 08:42:34 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD7FE13501 for ; Sun, 5 Mar 2023 05:41:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678023708; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=P/j9durd7jwFNaERdOWNyEIRSGeMnTudRhB5H/p/vA4=; b=Ir1ZffX0F6wAzNhWJzuH6JdoJ/U5gcEiuG+5eSNI79D7EB4z9DShyFarRiuvg6L2jJnbur harpAz1c06sRwkhvUaMs7HrYD+jvDtEbZrjNTMpjtJaRYvY95p5njJurkpgXXpiQleVlhc qZBvQQHgaBWafBFzWbcirqeGI+GfgrU= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-659-pgC5_pukO-KO-VBM7OMrlQ-1; Sun, 05 Mar 2023 08:41:43 -0500 X-MC-Unique: pgC5_pukO-KO-VBM7OMrlQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id EBC9329AA38F; Sun, 5 Mar 2023 13:41:42 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A76DBC16029; Sun, 5 Mar 2023 13:41:42 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 14CA9401344B4; Sun, 5 Mar 2023 10:41:23 -0300 (-03) Message-ID: <20230305133657.255737580@redhat.com> User-Agent: quilt/0.67 Date: Sun, 05 Mar 2023 10:36:57 -0300 From: Marcelo Tosatti To: Christoph Lameter Cc: Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Russell King , Huacai Chen , Heiko Carstens , x86@kernel.org Subject: [PATCH v4 00/12] fold per-CPU vmstats remotely X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch series addresses 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 By having vmstat_shepherd flush the per-CPU counters to the global counters from remote CPUs. This is done using cmpxchg to manipulate the counters, both CPU locally (via the account functions), and remotely (via cpu_vm_stats_fold). Thanks to Aaron Tomlin for diagnosing issue 1 and writing the initial patch series. v4: - Switch per-CPU vmstat counters to s32, required for architectures that do not provide cmpxchg/xchg on 8 bits v3: - Removed unused drain_zone_pages and changes variable (David Hildenbrand) - Use xchg instead of cmpxchg in refresh_cpu_vm_stats (Peter Xu) - Add drain_all_pages to vmstat_refresh to make stats more accurate (Peter Xu) - Improve changelog of "mm/vmstat: switch counter modification to cmpxchg" (Peter Xu / David) - Improve changelog of "mm/vmstat: remove remote node draining" (David Hildenbrand) v2: - actually use LOCK CMPXCHG on counter mod/inc/dec functions (Christoph Lameter) - use try_cmpxchg for cmpxchg loops (Uros Bizjak / Matthew Wilcox) arch/arm64/include/asm/percpu.h | 16 ++ arch/loongarch/include/asm/percpu.h | 23 +++ arch/s390/include/asm/percpu.h | 5 arch/x86/include/asm/percpu.h | 39 +++--- include/asm-generic/percpu.h | 17 ++ include/linux/mmzone.h | 11 - include/linux/percpu-defs.h | 2 kernel/fork.c | 2 kernel/scs.c | 2 mm/page_alloc.c | 23 --- mm/vmstat.c | 452 +++++++++++++++++++++++++++++++++++++++++------------------------------------ 11 files changed, 325 insertions(+), 267 deletions(-)