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[209.132.183.28]) by mx.google.com with ESMTPS id k129si12239140qkc.35.2019.06.19.02.07.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Jun 2019 02:07:34 -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-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 mx1.redhat.com (Postfix) with ESMTPS id 5220E223872; Wed, 19 Jun 2019 09:07:33 +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 D319C19C6A; Wed, 19 Jun 2019 09:07:31 +0000 (UTC) Subject: Re: [PATCH v2] mm/sparse: set section nid for hot-add memory To: Michal Hocko Cc: Oscar Salvador , 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> <20190619090405.GJ2968@dhcp22.suse.cz> 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: <20190619090405.GJ2968@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Wed, 19 Jun 2019 09:07:33 +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 11:04, Michal Hocko wrote: > On Wed 19-06-19 10:51:47, David Hildenbrand wrote: >> 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. > > NODE_NOT_IN_PAGE_FLAGS is an implementation detail on where the > information is stored. Yes and no. Storing it per section clearly doesn't allow storing node information on smaller granularity, like storing in page->flags does. So no, it is not only an implementation detail. I cannot say how much it is really needed now but > I can see there will be a demand for it in a longer term because > page->flags space is scarce and very interesting storage. So I do not > see it go away I am afraid. Depends on how performance-critical pfn_to_nid() is. I can't tell. -- Thanks, David / dhildenb