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[209.132.180.67]) by mx.google.com with ESMTP id w135si3534406oiw.44.2020.02.06.23.24.45; Thu, 06 Feb 2020 23:24:57 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=Av6DTn9d; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727243AbgBGHX1 (ORCPT + 99 others); Fri, 7 Feb 2020 02:23:27 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:20476 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726642AbgBGHX0 (ORCPT ); Fri, 7 Feb 2020 02:23:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581060204; 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=AEOHHq1NHXQs3ZsnGWPJx6llX/TbhDB3MJJr3fAxidE=; b=Av6DTn9dvo7Bg9o58V/82EUXPA1l0Y8TkKxXlJ7AX0sQr1KetubIeD+irYUut/ZrHQ9bIl duhycVjlnULad8L1hh/3NDrz46Zc/lXPv7LvEzqvHeYsqWAczgQbNCJ+eoHbDTDbLIw8QJ G/1E5lt9QoU4lvsQLCoAPuf/Zk9/HBQ= 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-140-Suz8BHsCNou3jELJ_ApsZg-1; Fri, 07 Feb 2020 02:23:21 -0500 X-MC-Unique: Suz8BHsCNou3jELJ_ApsZg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ADBD6801A01; Fri, 7 Feb 2020 07:23:19 +0000 (UTC) Received: from localhost (ovpn-12-30.pek2.redhat.com [10.72.12.30]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F196E5DA7D; Fri, 7 Feb 2020 07:23:16 +0000 (UTC) Date: Fri, 7 Feb 2020 15:23:13 +0800 From: Baoquan He To: David Hildenbrand Cc: Wei Yang , akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/sparsemem: pfn_to_page is not valid yet on SPARSEMEM Message-ID: <20200207072313.GH26758@MiWiFi-R3L-srv> References: <20200206125343.9070-1-richardw.yang@linux.intel.com> <6d9e36cb-ee4a-00c8-447b-9b75a0262c3a@redhat.com> <20200206135016.GA25537@MiWiFi-R3L-srv> <87bb4563-481d-cce9-b916-50a098558210@redhat.com> <20200206140703.GB25537@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/06/20 at 03:37pm, David Hildenbrand wrote: > On 06.02.20 15:07, Baoquan He wrote: > > On 02/06/20 at 02:55pm, David Hildenbrand wrote: > >> On 06.02.20 14:50, Baoquan He wrote: > >>> On 02/06/20 at 02:28pm, David Hildenbrand wrote: > >>>> On 06.02.20 13:53, Wei Yang wrote: > >>>>> When we use SPARSEMEM instead of SPARSEMEM_VMEMMAP, pfn_to_page() > >>>>> doesn't work before sparse_init_one_section() is called. This leads to a > >>>>> crash when hotplug memory. > >>>>> > >>>>> We should use memmap as it did. > >>>>> > >>>>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > >>>>> Signed-off-by: Wei Yang > >>>>> CC: Dan Williams > >>>>> --- > >>>>> mm/sparse.c | 2 +- > >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>>>> > >>>>> diff --git a/mm/sparse.c b/mm/sparse.c > >>>>> index 5a8599041a2a..2efb24ff8f96 100644 > >>>>> --- a/mm/sparse.c > >>>>> +++ b/mm/sparse.c > >>>>> @@ -882,7 +882,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn, > >>>>> * Poison uninitialized struct pages in order to catch invalid flags > >>>>> * combinations. > >>>>> */ > >>>>> - page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages); > >>>>> + page_init_poison(memmap, sizeof(struct page) * nr_pages); > >>>> > >>>> If you add sub-sections that don't fall onto the start of the section, > >>>> > >>>> pfn_to_page(start_pfn) != memmap > >>>> > >>>> and your patch would break that under SPARSEMEM_VMEMMAP if I am not wrong. > >>> > >>> It returns the pfn_to_page(pfn) from __populate_section_memmap() and > >>> assign to memmap in vmemmap case, how come it breaks anything. Correct > >>> me if I was wrong. > >> > >> I'm sorry, I can't follow :) Can you elaborate? > >> > >> Was your comment targeted at why the old code cannot be broken or why > >> this patch cannot be broken? > > > > Sorry for the confusion :-) the latter. I mean the returned memmap has been > > at the pfn_to_page(start_pfn) in SPARSEMEM_VMEMMAP case. > > Yeah, at least for SPARSEMEM_VMEMMAP it is indeed right. Thanks :) > > > Now, about SPARSEMEM: > > populate_section_memmap() does not care about nr_pages and will allocate > a memmap for the whole section. So, whenever we add sub-sections to a > section, we allocate a new memmap for the whole section. And we do > overwrite the memmap pointer in our section. ( sparse_add_section() ) > > That makes me assume that sub-section hot-add under SPARSEMEM is either > > a) never enabled and only works with SPARSEMEM_VMEMMAP > b) horribly broken > > And I think a) applies (looking at pfn_section_valid()). Therefore, we > don't have to care about sub-section hot-add specifics (and I would be > broken already) Yeah, I have the same thought as you. And later Dan's words confirms it in another threaad.