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=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 A8389C388F2 for ; Mon, 2 Nov 2020 13:03:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5D555223BE for ; Mon, 2 Nov 2020 13:03:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728897AbgKBND3 (ORCPT ); Mon, 2 Nov 2020 08:03:29 -0500 Received: from mx2.suse.de ([195.135.220.15]:49978 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728487AbgKBND1 (ORCPT ); Mon, 2 Nov 2020 08:03:27 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id ED37FB02D; Mon, 2 Nov 2020 13:03:25 +0000 (UTC) Subject: Re: [PATCH] mm/compaction: count pages and stop correctly during page isolation. To: Yang Shi , Zi Yan Cc: Michal Hocko , Andrew Morton , Linux MM , Rik van Riel , Linux Kernel Mailing List , Minchan Kim References: <20201029200435.3386066-1-zi.yan@sent.com> <20201030094308.GG1478@dhcp22.suse.cz> <6CAAB1FC-2B41-490B-A67A-93063629C19B@nvidia.com> <20201030133625.GJ1478@dhcp22.suse.cz> From: Vlastimil Babka Message-ID: Date: Mon, 2 Nov 2020 14:03:25 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/30/20 7:55 PM, Yang Shi wrote: > On Fri, Oct 30, 2020 at 11:39 AM Zi Yan wrote: >> >> On 30 Oct 2020, at 14:33, Yang Shi wrote: >> >> > On Fri, Oct 30, 2020 at 6:36 AM Michal Hocko wrote: >> >> >> >> On Fri 30-10-20 08:20:50, Zi Yan wrote: >> >>> On 30 Oct 2020, at 5:43, Michal Hocko wrote: >> >>> >> >>>> [Cc Vlastimil] >> >>>> >> >>>> On Thu 29-10-20 16:04:35, Zi Yan wrote: >> >>>>> From: Zi Yan >> >>>>> >> >>>>> In isolate_migratepages_block, when cc->alloc_contig is true, we are >> >>>>> able to isolate compound pages, nr_migratepages and nr_isolated did not >> >>>>> count compound pages correctly, causing us to isolate more pages than we >> >>>>> thought. Use thp_nr_pages to count pages. Otherwise, we might be trapped >> >>>>> in too_many_isolated while loop, since the actual isolated pages can go >> >>>>> up to COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32, >> >>>>> since we stop isolation after cc->nr_migratepages reaches to >> >>>>> COMPACT_CLUSTER_MAX. >> >>>>> >> >>>>> In addition, after we fix the issue above, cc->nr_migratepages could >> >>>>> never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated, >> >>>>> thus page isolation could not stop as we intended. Change the isolation >> >>>>> stop condition to >=. >> >>>>> >> >>>>> Signed-off-by: Zi Yan >> >>>>> --- >> >>>>> mm/compaction.c | 8 ++++---- >> >>>>> 1 file changed, 4 insertions(+), 4 deletions(-) >> >>>>> >> >>>>> diff --git a/mm/compaction.c b/mm/compaction.c >> >>>>> index ee1f8439369e..0683a4999581 100644 >> >>>>> --- a/mm/compaction.c >> >>>>> +++ b/mm/compaction.c >> >>>>> @@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, >> >>>>> >> >>>>> isolate_success: >> >>>>> list_add(&page->lru, &cc->migratepages); >> >>>>> - cc->nr_migratepages++; >> >>>>> - nr_isolated++; >> >>>>> + cc->nr_migratepages += thp_nr_pages(page); >> >>>>> + nr_isolated += thp_nr_pages(page); >> >>>> >> >>>> Does thp_nr_pages work for __PageMovable pages? >> >>> >> >>> Yes. It is the same as compound_nr() but compiled >> >>> to 1 when THP is not enabled. >> >> >> >> I am sorry but I do not follow. First of all the implementation of the >> >> two is different and also I was asking about __PageMovable which should >> >> never be THP IIRC. Can they be compound though? >> > >> > I have the same question, can they be compound? If they can be >> > compound, PageTransHuge() can't tell from THP and compound movable >> > page, right? >> >> Right. I have updated the patch and use compound_nr instead. > > Thanks. Actually I'm wondering what kind of movable page could be > compound. Any real examples? Looks like there's currently none. Compaction also wouldn't work properly with movable pages with order>0 as the free page scanner looks for order-0 pages only. But it won't hurt to use compound_nr() anyway. >> >> — >> Best Regards, >> Yan Zi >