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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 9855BC433DF for ; Wed, 24 Jun 2020 03:52:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4BC9B2070E for ; Wed, 24 Jun 2020 03:52:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FCjlQEwn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4BC9B2070E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D88BB6B0002; Tue, 23 Jun 2020 23:52:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D386A6B0003; Tue, 23 Jun 2020 23:52:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C4ECB6B0007; Tue, 23 Jun 2020 23:52:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id AAA2C6B0002 for ; Tue, 23 Jun 2020 23:52:47 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 56A76181AC9CB for ; Wed, 24 Jun 2020 03:52:47 +0000 (UTC) X-FDA: 76962733974.27.ray51_250120126e41 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin27.hostedemail.com (Postfix) with ESMTP id 3111C3D663 for ; Wed, 24 Jun 2020 03:52:47 +0000 (UTC) X-HE-Tag: ray51_250120126e41 X-Filterd-Recvd-Size: 5726 Received: from us-smtp-delivery-1.mimecast.com (us-smtp-2.mimecast.com [205.139.110.61]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Wed, 24 Jun 2020 03:52:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592970766; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GepTlGXwej9PWMeaqwTbVbEVkJTWG3Rdtwgufbgc7OA=; b=FCjlQEwnVJcHMggUNbglu6VhJTVgGwZn2iCU0+Ola64m1N+3dRgcTqz+/ds+lasDQlUd7j cKSl49ix+pVlWx3jUgtflF4d7cpLH8gwCHUhrNBTNpkSFN75rieytVLKz9XF4D6Qb8df3h kGwNwVx94PreK1LsyESMm3Z3SgZBaYc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-214-z8Nk-r7pP8693rTYXcsLQQ-1; Tue, 23 Jun 2020 23:52:44 -0400 X-MC-Unique: z8Nk-r7pP8693rTYXcsLQQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CF19A107ACCA; Wed, 24 Jun 2020 03:52:42 +0000 (UTC) Received: from localhost (ovpn-12-31.pek2.redhat.com [10.72.12.31]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 07EFB1A835; Wed, 24 Jun 2020 03:52:38 +0000 (UTC) Date: Wed, 24 Jun 2020 11:52:36 +0800 From: Baoquan He To: Wei Yang Cc: Dan Williams , Andrew Morton , Oscar Salvador , Linux MM , Linux Kernel Mailing List , David Hildenbrand Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section Message-ID: <20200624035236.GI3346@MiWiFi-R3L-srv> References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200624014737.GG3346@MiWiFi-R3L-srv> <20200624034638.GA10687@L-31X9LVDL-1304.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624034638.GA10687@L-31X9LVDL-1304.local> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Rspamd-Queue-Id: 3111C3D663 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 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. > > > paging_init() > > ->sparse_init() > > ->sparse_init_nid() > > { > > ... > > for_each_present_section_nr(pnum_begin, pnum) { > > ... > > map = __populate_section_memmap(pfn, PAGES_PER_SECTION, > > nid, NULL); > > ... > > } > > } > > ... > > ->zone_sizes_init() > > ->free_area_init() > > { > > for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) { > > subsection_map_init(start_pfn, end_pfn - start_pfn); > > } > > { > > > > __add_pages() > > ->sparse_add_section() > > ->section_activate() > > { > > ... > > fill_subsection_map(); > > if (nr_pages < PAGES_PER_SECTION && early_section(ms)) <----------********* > > return pfn_to_page(pfn); > > ... > > } > >> > > -- > Wei Yang > Help you, Help me >