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 3F1D2C636D7 for ; Wed, 1 Feb 2023 19:53:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231860AbjBATx3 (ORCPT ); Wed, 1 Feb 2023 14:53:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231916AbjBATxW (ORCPT ); Wed, 1 Feb 2023 14:53:22 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9B3218016D for ; Wed, 1 Feb 2023 11:52:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675281155; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=sTvWe2kfUoGBfAaCSxydSPRezZXDlplO8iSUUltKQvQ=; b=iSdWvokJmoXkJby0gG/mw1MytJVEeyFGVY7nZMzL/kjtdy6bWimpDHHur4Ub119Z7LJpPB XjM9eOPGAkPOBeAIQ8l829vPi/DXIvqHBuX5UAQ5sqftPU2aaJ4OFkg2UepIn2VpNXg9HR lvWu2/yf+uYBcs90oCPtXiAbpqV/u74= 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-664-FlzSg14TO-WC0NOa6ALVgw-1; Wed, 01 Feb 2023 14:52:30 -0500 X-MC-Unique: FlzSg14TO-WC0NOa6ALVgw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4975A2806051; Wed, 1 Feb 2023 19:52:30 +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 F40FD492B06; Wed, 1 Feb 2023 19:52:29 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 0A274403C1B83; Wed, 1 Feb 2023 16:51:49 -0300 (-03) Message-ID: <20230201195013.881721887@redhat.com> User-Agent: quilt/0.67 Date: Wed, 01 Feb 2023 16:50:13 -0300 From: Marcelo Tosatti To: Christoph Lameter Cc: Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 0/5] fold per-CPU vmstats remotely X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 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. include/linux/mmzone.h | 3 mm/vmstat.c | 424 ++++++++++++++++++++++++++++++++++++++++++++++++------------------------------------------ 2 files changed, 230 insertions(+), 197 deletions(-)