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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 6FA37C072B5 for ; Fri, 24 May 2019 06:00:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B9A820851 for ; Fri, 24 May 2019 06:00:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731820AbfEXGAI (ORCPT ); Fri, 24 May 2019 02:00:08 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:41636 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725886AbfEXGAH (ORCPT ); Fri, 24 May 2019 02:00:07 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0TSXfk8M_1558677600; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TSXfk8M_1558677600) by smtp.aliyun-inc.com(127.0.0.1); Fri, 24 May 2019 14:00:01 +0800 Subject: Re: [v4 PATCH 2/2] mm: vmscan: correct some vmscan counters for To: Hillf Danton Cc: ying.huang@intel.com, hannes@cmpxchg.org, mhocko@suse.com, mgorman@techsingularity.net, kirill.shutemov@linux.intel.com, josef@toxicpanda.com, hughd@google.com, shakeelb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190524055125.3036-1-hdanton@sina.com> From: Yang Shi Message-ID: Date: Fri, 24 May 2019 14:00:00 +0800 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: <20190524055125.3036-1-hdanton@sina.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 5/24/19 1:51 PM, Hillf Danton wrote: > On Fri, 24 May 2019 09:27:02 +0800 Yang Shi wrote: >> On 5/23/19 11:51 PM, Hillf Danton wrote: >>> On Thu, 23 May 2019 10:27:38 +0800 Yang Shi wrote: >>>> @ -1642,14 +1650,14 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, >>>> unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 }; >>>> unsigned long nr_skipped[MAX_NR_ZONES] = { 0, }; >>>> unsigned long skipped = 0; >>>> - unsigned long scan, total_scan, nr_pages; >>>> + unsigned long scan, total_scan; >>>> + unsigned long nr_pages; >>> Change for no earn:) >> Aha, yes. >> >>>> LIST_HEAD(pages_skipped); >>>> isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED); >>>> + total_scan = 0; >>>> scan = 0; >>>> - for (total_scan = 0; >>>> - scan < nr_to_scan && nr_taken < nr_to_scan && !list_empty(src); >>>> - total_scan++) { >>>> + while (scan < nr_to_scan && !list_empty(src)) { >>>> struct page *page; >>> AFAICS scan currently prevents us from looping for ever, while nr_taken bails >>> us out once we get what's expected, so I doubt it makes much sense to cut >>> nr_taken off. >> It is because "scan < nr_to_scan && nr_taken >= nr_to_scan" is >> impossible now with the units fixed. >> > With the units fixed, nr_taken is no longer checked. It is because scan would be always >= nr_taken. > >>>> page = lru_to_page(src); >>>> @@ -1657,9 +1665,12 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, >>>> VM_BUG_ON_PAGE(!PageLRU(page), page); >>>> + nr_pages = 1 << compound_order(page); >>>> + total_scan += nr_pages; >>>> + >>>> if (page_zonenum(page) > sc->reclaim_idx) { >>>> list_move(&page->lru, &pages_skipped); >>>> - nr_skipped[page_zonenum(page)]++; >>>> + nr_skipped[page_zonenum(page)] += nr_pages; >>>> continue; >>>> } >>>> @@ -1669,10 +1680,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, >>>> * ineligible pages. This causes the VM to not reclaim any >>>> * pages, triggering a premature OOM. >>>> */ >>>> - scan++; >>>> + scan += nr_pages; >>> The comment looks to defy the change if we fail to add a huge page to >>> the dst list; otherwise nr_taken knows how to do the right thing. What >>> I prefer is to let scan to do one thing a time. >> I don't get your point. Do you mean the comment "Do not count skipped >> pages because that makes the function return with no isolated pages if >> the LRU mostly contains ineligible pages."? I'm supposed the comment is >> used to explain why not count skipped page. >> > Well consider the case where there is a huge page in the second place > reversely on the src list along with other 20 regular pages, and we are > not able to add the huge page to the dst list. Currently we can go on and > try to scan other pages, provided nr_to_scan is 32; with the units fixed, > however, scan goes over nr_to_scan, leaving us no chance to scan any page > that may be not busy. I wonder that triggers a premature OOM, because I > think scan means the number of list nodes we try to isolate, and > nr_taken the number of regular pages successfully isolated. Yes, good point. I think I just need roll back to what v3 did here to get scan accounted for each case separately to avoid the possible over-account. >>>> switch (__isolate_lru_page(page, mode)) { >>>> case 0: >>>> - nr_pages = hpage_nr_pages(page); >>>> nr_taken += nr_pages; >>>> nr_zone_taken[page_zonenum(page)] += nr_pages; >>>> list_move(&page->lru, dst); >>>> -- >>>> 1.8.3.1 > Best Regards > Hillf