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 9BD7CC64ED8 for ; Mon, 27 Feb 2023 19:42:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230025AbjB0Tmt (ORCPT ); Mon, 27 Feb 2023 14:42:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51424 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229547AbjB0Tmr (ORCPT ); Mon, 27 Feb 2023 14:42:47 -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 EE76626CE8 for ; Mon, 27 Feb 2023 11:41:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1677526904; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=T5EHg8kPWMCSbaL6BDDyElln71bXn4w1AjwdqeSKwPo=; b=iQmaOWCsU3XGPvwj2oMBP3H046v0X5T63wZU3OHKbm5ycR/RPCMF3KIcuCgniRK/7mm+1f tu3ee+M5sFdXX1Nop7i+mHWtY55aBEVXRECIKEOOXji5LfQHdYfQmbwcrWR8nyLS4QTVSv Rt0BTBZ3+Ri1JYs3GC4gTimk7XAOFbc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-474-9Y3So9MEM_SG5dyC6CCJ3Q-1; Mon, 27 Feb 2023 14:41:40 -0500 X-MC-Unique: 9Y3So9MEM_SG5dyC6CCJ3Q-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 15529857D07; Mon, 27 Feb 2023 19:41:40 +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 A5613140EBF4; Mon, 27 Feb 2023 19:41:39 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id F3A0E403BC530; Mon, 27 Feb 2023 16:41:18 -0300 (-03) Date: Mon, 27 Feb 2023 16:41:18 -0300 From: Marcelo Tosatti To: Hillf Danton 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 Message-ID: References: <20230209150150.380060673@redhat.com> <20230224023410.2940-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230224023410.2940-1-hdanton@sina.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 24, 2023 at 10:34:10AM +0800, Hillf Danton wrote: > 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/ Only if you disable per-CPU vmstat counters for isolated CPUs (then maintenance of the data structures in isolated CPUs is not necessary). Which would be terrible for performance, however.