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 X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEFBAC47089 for ; Thu, 27 May 2021 10:52:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B20E5613D8 for ; Thu, 27 May 2021 10:52:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236285AbhE0KyU (ORCPT ); Thu, 27 May 2021 06:54:20 -0400 Received: from outbound-smtp47.blacknight.com ([46.22.136.64]:46465 "EHLO outbound-smtp47.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236221AbhE0KyR (ORCPT ); Thu, 27 May 2021 06:54:17 -0400 Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp47.blacknight.com (Postfix) with ESMTPS id C4608FB19B for ; Thu, 27 May 2021 11:52:43 +0100 (IST) Received: (qmail 18388 invoked from network); 27 May 2021 10:52:43 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.23.168]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 27 May 2021 10:52:43 -0000 Date: Thu, 27 May 2021 11:52:41 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Hillf Danton , Dave Hansen , Michal Hocko , LKML , Linux-MM Subject: Re: [PATCH 2/6] mm/page_alloc: Disassociate the pcp->high from pcp->batch Message-ID: <20210527105241.GB30378@techsingularity.net> References: <20210525080119.5455-1-mgorman@techsingularity.net> <20210525080119.5455-3-mgorman@techsingularity.net> <10cb326c-b4ad-3a82-a38b-aba7d2192736@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <10cb326c-b4ad-3a82-a38b-aba7d2192736@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 26, 2021 at 08:14:13PM +0200, Vlastimil Babka wrote: > > @@ -6698,11 +6717,10 @@ static void __zone_set_pageset_high_and_batch(struct zone *zone, unsigned long h > > */ > > static void zone_set_pageset_high_and_batch(struct zone *zone) > > { > > - unsigned long new_high, new_batch; > > + int new_high, new_batch; > > > > - new_batch = zone_batchsize(zone); > > - new_high = 6 * new_batch; > > - new_batch = max(1UL, 1 * new_batch); > > + new_batch = max(1, zone_batchsize(zone)); > > + new_high = zone_highsize(zone, new_batch); > > > > if (zone->pageset_high == new_high && > > zone->pageset_batch == new_batch) > > @@ -8170,6 +8188,12 @@ static void __setup_per_zone_wmarks(void) > > zone->_watermark[WMARK_LOW] = min_wmark_pages(zone) + tmp; > > zone->_watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2; > > > > + /* > > + * The watermark size have changed so update the pcpu batch > > + * and high limits or the limits may be inappropriate. > > + */ > > + zone_set_pageset_high_and_batch(zone); > > Hm so this puts the call in the path of various watermark related sysctl > handlers, but it's not protected by pcp_batch_high_lock. The zone lock won't > help against zone_pcp_update() from a hotplug handler. On the other hand, since > hotplug handlers also call __setup_per_zone_wmarks(), the zone_pcp_update() > calls there are now redundant and could be removed, no? > But later there will be a new sysctl in patch 6/6 using pcp_batch_high_lock, > thus that one will not be protected against the watermark related sysctl > handlers that reach here. > > To solve all this, seems like the static lock in setup_per_zone_wmarks() could > become a top-level visible lock and pcp high/batch updates could switch to that > one instead of own pcp_batch_high_lock. And zone_pcp_update() calls from hotplug > handlers could be removed. > Hmm, the locking has very different hold times. The static lock in setup_per_zone_wmarks is a spinlock that protects against parallel updates of watermarks and is held for a short duration. The pcp_batch_high_lock is a mutex that is held for a relatively long time while memory is being offlined and can sleep. Memory hotplug updates the watermarks without pcp_batch_high_lock held so overall, unifying the locking there should be a separate series. How about this as a fix for this patch? ---8<--- mm/page_alloc: Disassociate the pcp->high from pcp->batch -fix Vlastimil Babka noted that __setup_per_zone_wmarks updating pcp->high did not protect watermark-related sysctl handlers from a parallel memory hotplug operations. This patch moves the PCP update to setup_per_zone_wmarks and updates the PCP high value while protected by the pcp_batch_high_lock mutex. This is a fix to the mmotm patch mm-page_alloc-disassociate-the-pcp-high-from-pcp-batch.patch. It'll cause a conflict with mm-page_alloc-adjust-pcp-high-after-cpu-hotplug-events.patch but the resolution is simply to change the caller in setup_per_zone_wmarks to zone_pcp_update(zone, 0) Signed-off-by: Mel Gorman --- mm/page_alloc.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 329b71e41db4..b1b3c66e9d88 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8199,12 +8199,6 @@ static void __setup_per_zone_wmarks(void) zone->_watermark[WMARK_LOW] = min_wmark_pages(zone) + tmp; zone->_watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2; - /* - * The watermark size have changed so update the pcpu batch - * and high limits or the limits may be inappropriate. - */ - zone_set_pageset_high_and_batch(zone); - spin_unlock_irqrestore(&zone->lock, flags); } @@ -8221,11 +8215,19 @@ static void __setup_per_zone_wmarks(void) */ void setup_per_zone_wmarks(void) { + struct zone *zone; static DEFINE_SPINLOCK(lock); spin_lock(&lock); __setup_per_zone_wmarks(); spin_unlock(&lock); + + /* + * The watermark size have changed so update the pcpu batch + * and high limits or the limits may be inappropriate. + */ + for_each_zone(zone) + zone_pcp_update(zone); } /*