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 0081DC636D7 for ; Thu, 9 Feb 2023 15:34:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230022AbjBIPeV (ORCPT ); Thu, 9 Feb 2023 10:34:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42448 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230411AbjBIPeI (ORCPT ); Thu, 9 Feb 2023 10:34:08 -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 8A6DB32E51 for ; Thu, 9 Feb 2023 07:33:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675956800; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=vcrcLyyXGvx1agmSjax9RNBo44/wgLryjaESGOqOIAs=; b=SQ1XHFRfHmAeQP2E7G5cLMPCt9QGbJQaGVV2QwJZNiJ0p0fu/XSNIvrV4w+SYrs/zjNLAK DqfFSfI/QGGQOMf3a6Rcydp7ZNTJ1vV06KGnyDGZ3qMKRm5ngkNWnrYKJGa+ZbudXyp4JO bNmAGGiJKErKdcjHVzZ0/hZ9ggTGKvA= 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-19-QmJbcTqeOtaOCHDJgUQZlw-1; Thu, 09 Feb 2023 10:33:19 -0500 X-MC-Unique: QmJbcTqeOtaOCHDJgUQZlw-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 C95FD3C10ED4; Thu, 9 Feb 2023 15:33:14 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-3.gru2.redhat.com [10.97.112.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A00D4C16022; Thu, 9 Feb 2023 15:33:14 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 60375403CC068; Thu, 9 Feb 2023 12:32:51 -0300 (-03) Message-ID: <20230209150150.380060673@redhat.com> User-Agent: quilt/0.67 Date: Thu, 09 Feb 2023 12:01:50 -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 v2 00/11] 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. 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 | 3 kernel/fork.c | 2 kernel/scs.c | 2 mm/vmstat.c | 424 ++++++++++++++++++++++++++++++++++++++++++++++++------------------------------------------ 9 files changed, 308 insertions(+), 223 deletions(-)