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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY 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 8E63AC433DF for ; Wed, 24 Jun 2020 06:13:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 41F622078A for ; Wed, 24 Jun 2020 06:13:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 41F622078A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 760146B0002; Wed, 24 Jun 2020 02:13:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6EA1F6B0003; Wed, 24 Jun 2020 02:13:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5D8986B0005; Wed, 24 Jun 2020 02:13:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0159.hostedemail.com [216.40.44.159]) by kanga.kvack.org (Postfix) with ESMTP id 422816B0002 for ; Wed, 24 Jun 2020 02:13:47 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id CFFC38245571 for ; Wed, 24 Jun 2020 06:13:46 +0000 (UTC) X-FDA: 76963089252.04.money36_631227126e41 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id A9897800763A for ; Wed, 24 Jun 2020 06:13:46 +0000 (UTC) X-HE-Tag: money36_631227126e41 X-Filterd-Recvd-Size: 3529 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) by imf13.hostedemail.com (Postfix) with ESMTP for ; Wed, 24 Jun 2020 06:13:45 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01355;MF=richard.weiyang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0U0Zjl4J_1592979220; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0U0Zjl4J_1592979220) by smtp.aliyun-inc.com(127.0.0.1); Wed, 24 Jun 2020 14:13:40 +0800 Date: Wed, 24 Jun 2020 14:13:40 +0800 From: Wei Yang To: Michal Hocko Cc: Wei Yang , akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, linux-mm@kvack.org, bhe@redhat.com, linux-kernel@vger.kernel.org, david@redhat.com Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section Message-ID: <20200624061340.GA11552@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200623151828.GA31426@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623151828.GA31426@dhcp22.suse.cz> X-Rspamd-Queue-Id: A9897800763A X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 23, 2020 at 05:18:28PM +0200, Michal Hocko wrote: >On Tue 23-06-20 17:42:58, Wei Yang wrote: >> For early sections, we assumes its memmap will never be partially >> removed. But current behavior breaks this. >> >> Let's correct it. >> >> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") >> Signed-off-by: Wei Yang > >Can a user trigger this or is this a theoretical bug? Let me rewrite the changelog a little. Look forward any comments. For early sections, its memmap is handled specially even sub-section is enabled. The memmap could only be populated as a whole. Quoted from the comment of section_activate(): * The early init code does not consider partially populated * initial sections, it simply assumes that memory will never be * referenced. If we hot-add memory into such a section then we * do not need to populate the memmap and can simply reuse what * is already there. While current section_deactivate() breaks this rule. When hot-remove a sub-section, section_deactivate() would depopulate its memmap. The consequence is if we hot-add this subsection again, its memmap never get proper populated. > >> --- >> mm/sparse.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/mm/sparse.c b/mm/sparse.c >> index b2b9a3e34696..1a0069f492f5 100644 >> --- a/mm/sparse.c >> +++ b/mm/sparse.c >> @@ -825,10 +825,10 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, >> ms->section_mem_map &= ~SECTION_HAS_MEM_MAP; >> } >> >> - if (section_is_early && memmap) >> - free_map_bootmem(memmap); >> - else >> + if (!section_is_early) > >This begs a comment. > >> depopulate_section_memmap(pfn, nr_pages, altmap); >> + else if (memmap) >> + free_map_bootmem(memmap); >> >> if (empty) >> ms->section_mem_map = (unsigned long)NULL; >> -- >> 2.20.1 (Apple Git-117) >> > >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me