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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,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 E80F9C06510 for ; Mon, 1 Jul 2019 21:50:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9A6D21479 for ; Mon, 1 Jul 2019 21:50:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727070AbfGAVuQ (ORCPT ); Mon, 1 Jul 2019 17:50:16 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:50380 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727028AbfGAVuQ (ORCPT ); Mon, 1 Jul 2019 17:50:16 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R501e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04391;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0TVobKD8_1562017791; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TVobKD8_1562017791) by smtp.aliyun-inc.com(127.0.0.1); Tue, 02 Jul 2019 05:50:07 +0800 Subject: Re: [PATCH v2] mm, vmscan: prevent useless kswapd loops To: Shakeel Butt , Johannes Weiner , Mel Gorman , Michal Hocko , Andrew Morton , Vlastimil Babka , Hillf Danton , Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190701201847.251028-1-shakeelb@google.com> From: Yang Shi Message-ID: <350a5c6f-4cf2-953e-7b6c-89460b11d297@linux.alibaba.com> Date: Mon, 1 Jul 2019 14:49:50 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20190701201847.251028-1-shakeelb@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/1/19 1:18 PM, Shakeel Butt wrote: > On production we have noticed hard lockups on large machines running > large jobs due to kswaps hoarding lru lock within isolate_lru_pages when > sc->reclaim_idx is 0 which is a small zone. The lru was couple hundred > GiBs and the condition (page_zonenum(page) > sc->reclaim_idx) in > isolate_lru_pages was basically skipping GiBs of pages while holding the > LRU spinlock with interrupt disabled. > > On further inspection, it seems like there are two issues: > > 1) If the kswapd on the return from balance_pgdat() could not sleep > (i.e. node is still unbalanced), the classzone_idx is unintentionally > set to 0 and the whole reclaim cycle of kswapd will try to reclaim > only the lowest and smallest zone while traversing the whole memory. > > 2) Fundamentally isolate_lru_pages() is really bad when the allocation > has woken kswapd for a smaller zone on a very large machine running very > large jobs. It can hoard the LRU spinlock while skipping over 100s of > GiBs of pages. > > This patch only fixes the (1). The (2) needs a more fundamental solution. > To fix (1), in the kswapd context, if pgdat->kswapd_classzone_idx is > invalid use the classzone_idx of the previous kswapd loop otherwise use > the one the waker has requested. > > Fixes: e716f2eb24de ("mm, vmscan: prevent kswapd sleeping prematurely > due to mismatched classzone_idx") > > Signed-off-by: Shakeel Butt > --- > Changelog since v1: > - fixed the patch based on Yang Shi's comment. > > mm/vmscan.c | 27 +++++++++++++++------------ > 1 file changed, 15 insertions(+), 12 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 9e3292ee5c7c..eacf87f07afe 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3760,19 +3760,18 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) > } > > /* > - * pgdat->kswapd_classzone_idx is the highest zone index that a recent > - * allocation request woke kswapd for. When kswapd has not woken recently, > - * the value is MAX_NR_ZONES which is not a valid index. This compares a > - * given classzone and returns it or the highest classzone index kswapd > - * was recently woke for. > + * The pgdat->kswapd_classzone_idx is used to pass the highest zone index to be > + * reclaimed by kswapd from the waker. If the value is MAX_NR_ZONES which is not > + * a valid index then either kswapd runs for first time or kswapd couldn't sleep > + * after previous reclaim attempt (node is still unbalanced). In that case > + * return the zone index of the previous kswapd reclaim cycle. > */ > static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat, > - enum zone_type classzone_idx) > + enum zone_type prev_classzone_idx) > { > if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES) > - return classzone_idx; > - > - return max(pgdat->kswapd_classzone_idx, classzone_idx); > + return prev_classzone_idx; > + return pgdat->kswapd_classzone_idx; > } > > static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order, > @@ -3908,7 +3907,7 @@ static int kswapd(void *p) > > /* Read the new order and classzone_idx */ > alloc_order = reclaim_order = pgdat->kswapd_order; > - classzone_idx = kswapd_classzone_idx(pgdat, 0); > + classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx); > pgdat->kswapd_order = 0; > pgdat->kswapd_classzone_idx = MAX_NR_ZONES; > > @@ -3961,8 +3960,12 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order, > if (!cpuset_zone_allowed(zone, gfp_flags)) > return; > pgdat = zone->zone_pgdat; > - pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, > - classzone_idx); > + > + if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES) > + pgdat->kswapd_classzone_idx = classzone_idx; > + else > + pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, > + classzone_idx); > pgdat->kswapd_order = max(pgdat->kswapd_order, order); > if (!waitqueue_active(&pgdat->kswapd_wait)) > return; I agree the manipulation to classzone_idx looks convoluted. This version looks correct to me. You could add: Reviewed-by: Yang Shi