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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67774C678D5 for ; Fri, 24 Feb 2023 02:34:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A90D96B0072; Thu, 23 Feb 2023 21:34:28 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A40FC6B0073; Thu, 23 Feb 2023 21:34:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 908106B0074; Thu, 23 Feb 2023 21:34:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 7E1F36B0072 for ; Thu, 23 Feb 2023 21:34:28 -0500 (EST) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 4B24C1C6A9F for ; Fri, 24 Feb 2023 02:34:28 +0000 (UTC) X-FDA: 80500616616.05.59581DC Received: from mail3-167.sinamail.sina.com.cn (mail3-167.sinamail.sina.com.cn [202.108.3.167]) by imf27.hostedemail.com (Postfix) with ESMTP id 3EF0540013 for ; Fri, 24 Feb 2023 02:34:24 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=none; spf=pass (imf27.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.167 as permitted sender) smtp.mailfrom=hdanton@sina.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1677206066; a=rsa-sha256; cv=none; b=V6R/0IW4TuE8pp+IPjSpd/vV3+Z1b4SeIvpCiDi7CKCJNK5F7xoxY2kSKeDCaH1vq6eIGW vcQTLQT0NDK4zMtPN/+DWKkZl0NBPf9YZpiGB4kBNxiRpJ8dGBsqhIL/ksOK6Ar88e072d VPzc11xWm+sbtye3qw4wVhpiZQdjV0c= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=none; spf=pass (imf27.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.167 as permitted sender) smtp.mailfrom=hdanton@sina.com; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1677206066; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XY6VumKPij88F2SsgQZJ/+iJlLhHCrTcgI5ZM+MLuVY=; b=N+FWRfxSFBJ3jhAte+gpNZhJcvkhGpghI/KJdvfsvcB5YV9iDZlaYSUR1kfmPnFWA4CDdT j7/QTjG8zsS0nzkQmb5Fb5z+COSVEBPLY3GSsDFk0Wp1nZp+BLcv7Osh6Zt0+H9zMhEnhH 0kpKZ8fI3Tv0ilrqh8iayAfpg7Q1W2w= Received: from unknown (HELO localhost.localdomain)([114.249.61.130]) by sina.com (172.16.97.32) with ESMTP id 63F822230003110C; Fri, 24 Feb 2023 10:34:12 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 734117676174 From: Hillf Danton To: Marcelo Tosatti Cc: Christoph Lameter , Andrew Morton , Aaron Tomlin , Frederic Weisbecker , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 00/11] fold per-CPU vmstats remotely Date: Fri, 24 Feb 2023 10:34:10 +0800 Message-Id: <20230224023410.2940-1-hdanton@sina.com> In-Reply-To: References: <20230209150150.380060673@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 3EF0540013 X-Rspamd-Server: rspam01 X-Stat-Signature: po4ds955ib6i3g4oyg4ppq3pdcjpuruy X-HE-Tag: 1677206064-435551 X-HE-Meta: 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 7aNhes6z SUaudJqL4j9AJBZZJqX0t1Pkyffvj6CX574lDnUwFft1RK1ZWtkAbCceLxj5cC6Tj5xO5jB9AglOmICCR9tRV0bf//F6R443mWFAbMIyKnWwen2+LpICmsvuQ8LRTmKP1RmgXEXjuw1awW53J0BYLqLMWfw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Feb 09, 2023 at 12:01:50PM -0300, Marcelo Tosatti wrote: > 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). Frankly another case of bandaid[1] ? [1] https://lore.kernel.org/lkml/20230223150624.GA29739@lst.de/