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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY autolearn=no 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 94B0DC433E1 for ; Wed, 24 Jun 2020 22:05:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6495220768 for ; Wed, 24 Jun 2020 22:05:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6495220768 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 DEB546B0003; Wed, 24 Jun 2020 18:05:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D784A6B0005; Wed, 24 Jun 2020 18:05:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C3C846B0007; Wed, 24 Jun 2020 18:05:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0153.hostedemail.com [216.40.44.153]) by kanga.kvack.org (Postfix) with ESMTP id A52AD6B0003 for ; Wed, 24 Jun 2020 18:05:57 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 22B71181ABE87 for ; Wed, 24 Jun 2020 22:05:57 +0000 (UTC) X-FDA: 76965488754.14.arch78_460d20426e47 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin14.hostedemail.com (Postfix) with ESMTP id 04EB018229837 for ; Wed, 24 Jun 2020 22:05:56 +0000 (UTC) X-HE-Tag: arch78_460d20426e47 X-Filterd-Recvd-Size: 3668 Received: from out30-43.freemail.mail.aliyun.com (out30-43.freemail.mail.aliyun.com [115.124.30.43]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Wed, 24 Jun 2020 22:05:55 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R821e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=richard.weiyang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0U0d59pt_1593036352; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0U0d59pt_1593036352) by smtp.aliyun-inc.com(127.0.0.1); Thu, 25 Jun 2020 06:05:52 +0800 Date: Thu, 25 Jun 2020 06:05:52 +0800 From: Wei Yang To: Dan Williams Cc: Wei Yang , Michal Hocko , Andrew Morton , Oscar Salvador , Linux MM , Baoquan He , Linux Kernel Mailing List , David Hildenbrand Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section Message-ID: <20200624220552.GA15016@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200623151828.GA31426@dhcp22.suse.cz> <20200624061340.GA11552@L-31X9LVDL-1304.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 04EB018229837 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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 Wed, Jun 24, 2020 at 09:10:09AM -0700, Dan Williams wrote: >On Tue, Jun 23, 2020 at 11:14 PM Wei Yang > wrote: >> >> 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. > >Ok, forgive the latency as re-fetched this logic into my mental cache. >So what I was remembering was the initial state of the code that >special cased early sections, and that still seems to be the case in >pfn_valid(). IIRC early_sections / bootmem are blocked from being >removed entirely. Partial / subsection removals are ok. Would you mind giving more words? Partial subsection removal is ok, so no need to fix this? -- Wei Yang Help you, Help me