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[209.132.183.28]) by mx.google.com with ESMTPS id n94si566901qte.210.2019.06.19.01.52.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Jun 2019 01:52:03 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0913630018E9; Wed, 19 Jun 2019 08:51:50 +0000 (UTC) Received: from [10.36.117.229] (ovpn-117-229.ams2.redhat.com [10.36.117.229]) by smtp.corp.redhat.com (Postfix) with ESMTP id A095D60A9A; Wed, 19 Jun 2019 08:51:48 +0000 (UTC) Subject: Re: [PATCH v2] mm/sparse: set section nid for hot-add memory To: Oscar Salvador , Michal Hocko Cc: Wei Yang , linux-mm@kvack.org, akpm@linux-foundation.org, anshuman.khandual@arm.com References: <20190618005537.18878-1-richardw.yang@linux.intel.com> <20190619062330.GB5717@dhcp22.suse.cz> <20190619075347.GA22552@linux> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190619075347.GA22552@linux> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Wed, 19 Jun 2019 08:52:02 +0000 (UTC) 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 19.06.19 09:53, Oscar Salvador wrote: > On Wed, Jun 19, 2019 at 08:23:30AM +0200, Michal Hocko wrote: >> On Tue 18-06-19 08:55:37, Wei Yang wrote: >>> In case of NODE_NOT_IN_PAGE_FLAGS is set, we store section's node id in >>> section_to_node_table[]. While for hot-add memory, this is missed. >>> Without this information, page_to_nid() may not give the right node id. >> >> Which would mean that NODE_NOT_IN_PAGE_FLAGS doesn't really work with >> the hotpluged memory, right? Any idea why nobody has noticed this >> so far? Is it because NODE_NOT_IN_PAGE_FLAGS is rare and essentially >> unused with the hotplug? page_to_nid providing an incorrect result >> sounds quite serious to me. > > The thing is that for NODE_NOT_IN_PAGE_FLAGS to be enabled we need to run out of > space in page->flags to store zone, nid and section. > Currently, even with the largest values (with pagetable level 5), that is not > possible on x86_64. > It is possible though, that somewhere in the future, when the values get larger > (e.g: we add more zones, NODE_SHIFT grows, or we need more space to store > the section) we finally run out of room for the flags though. > > I am not sure about the other arches though, we probably should audit them > and see which ones can fall in there. > I'd love to see NODE_NOT_IN_PAGE_FLAGS go. -- Thanks, David / dhildenb