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=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 7509BC433E1 for ; Wed, 24 Jun 2020 22:08:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3E53B2084D for ; Wed, 24 Jun 2020 22:08:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3E53B2084D 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 ADE086B0002; Wed, 24 Jun 2020 18:08:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A8DA06B0003; Wed, 24 Jun 2020 18:08:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9A2396B0005; Wed, 24 Jun 2020 18:08:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0155.hostedemail.com [216.40.44.155]) by kanga.kvack.org (Postfix) with ESMTP id 805EB6B0002 for ; Wed, 24 Jun 2020 18:08:54 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E90ED1EE6 for ; Wed, 24 Jun 2020 22:08:53 +0000 (UTC) X-FDA: 76965496146.14.spark80_4a06b3926e47 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin14.hostedemail.com (Postfix) with ESMTP id B584B18229818 for ; Wed, 24 Jun 2020 22:08:53 +0000 (UTC) X-HE-Tag: spark80_4a06b3926e47 X-Filterd-Recvd-Size: 4519 Received: from out30-44.freemail.mail.aliyun.com (out30-44.freemail.mail.aliyun.com [115.124.30.44]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Wed, 24 Jun 2020 22:08:52 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;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=8;SR=0;TI=SMTPD_---0U0dBAHt_1593036529; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0U0dBAHt_1593036529) by smtp.aliyun-inc.com(127.0.0.1); Thu, 25 Jun 2020 06:08:49 +0800 Date: Thu, 25 Jun 2020 06:08:49 +0800 From: Wei Yang To: David Hildenbrand Cc: Wei Yang , Baoquan He , Dan Williams , Andrew Morton , Oscar Salvador , Linux MM , Linux Kernel Mailing List Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section Message-ID: <20200624220849.GB15016@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200624014737.GG3346@MiWiFi-R3L-srv> <20200624034638.GA10687@L-31X9LVDL-1304.local> <20200624035236.GI3346@MiWiFi-R3L-srv> <20200624035622.GA10774@L-31X9LVDL-1304.local> <53f7f04e-9c77-a987-8206-bd572268522b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53f7f04e-9c77-a987-8206-bd572268522b@redhat.com> X-Rspamd-Queue-Id: B584B18229818 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 10:51:08AM +0200, David Hildenbrand wrote: >On 24.06.20 05:56, Wei Yang wrote: >> On Wed, Jun 24, 2020 at 11:52:36AM +0800, Baoquan He wrote: >>> On 06/24/20 at 11:46am, Wei Yang wrote: >>>> On Wed, Jun 24, 2020 at 09:47:37AM +0800, Baoquan He wrote: >>>>> On 06/23/20 at 05:21pm, Dan Williams wrote: >>>>>> On Tue, Jun 23, 2020 at 2:43 AM Wei Yang >>>>>> wrote: >>>>>>> >>>>>>> For early sections, we assumes its memmap will never be partially >>>>>>> removed. But current behavior breaks this. >>>>>> >>>>>> Where do we assume that? >>>>>> >>>>>> The primary use case for this was mapping pmem that collides with >>>>>> System-RAM in the same 128MB section. That collision will certainly be >>>>>> depopulated on-demand depending on the state of the pmem device. So, >>>>>> I'm not understanding the problem or the benefit of this change. >>>>> >>>>> I was also confused when review this patch, the patch log is a little >>>>> short and simple. From the current code, with SPARSE_VMEMMAP enabled, we >>>>> do build memmap for the whole memory section during boot, even though >>>>> some of them may be partially populated. We just mark the subsection map >>>>> for present pages. >>>>> >>>>> Later, if pmem device is mapped into the partially boot memory section, >>>>> we just fill the relevant subsection map, do return directly, w/o building >>>>> the memmap for it, in section_activate(). Because the memmap for the >>>>> unpresent RAM part have been there. I guess this is what Wei is trying to >>>>> do to keep the behaviour be consistent for pmem device adding, or >>>>> pmem device removing and later adding again. >>>>> >>>>> Please correct me if I am wrong. >>>> >>>> You are right here. >>>> >>>>> >>>>> To me, fixing it looks good. But a clear doc or code comment is >>>>> necessary so that people can understand the code with less time. >>>>> Leaving it as is doesn't cause harm. I personally tend to choose >>>>> the former. >>>>> >>>> >>>> The former is to add a clear doc? >>> >>> Sorry for the confusion. The former means the fix in your patch. Maybe a >>> improved log and some code comment adding can make it more perfect. >>> >> >> Sure, I would try to add more log and comments, in case you have some good >> suggestion, just let me know :) >> > >We have documented this is section_activate() and pfn_valid() >sufficiently. Maybe add a pointer like > >/* > * The memmap of early sections is always fully populated. See > * section_activate() and pfn_valid() . > */ Thanks, I have added this above the "if" check. > >-- >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me