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[209.132.183.28]) by mx.google.com with ESMTPS id b184si37036864qke.35.2019.08.01.02.18.48 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Aug 2019 02:18:48 -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 2FF1BC049D62; Thu, 1 Aug 2019 09:18:47 +0000 (UTC) Received: from [10.36.116.245] (ovpn-116-245.ams2.redhat.com [10.36.116.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id D633319C70; Thu, 1 Aug 2019 09:18:43 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory To: Michal Hocko Cc: Rashmica Gupta , Oscar Salvador , Andrew Morton , Dan Williams , pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190702074806.GA26836@linux> <20190731120859.GJ9330@dhcp22.suse.cz> <4ddee0dd719abd50350f997b8089fa26f6004c0c.camel@gmail.com> <20190801071709.GE11627@dhcp22.suse.cz> <9bcbd574-7e23-5cfe-f633-646a085f935a@redhat.com> <20190801072430.GF11627@dhcp22.suse.cz> <5e6137c9-5269-5756-beaa-d116652be8b9@redhat.com> <20190801073957.GH11627@dhcp22.suse.cz> <20190801074836.GI11627@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/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190801074836.GI11627@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 [10.5.110.31]); Thu, 01 Aug 2019 09:18:47 +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 01.08.19 09:48, Michal Hocko wrote: > On Thu 01-08-19 09:39:57, Michal Hocko wrote: >> On Thu 01-08-19 09:31:09, David Hildenbrand wrote: >>> On 01.08.19 09:26, David Hildenbrand wrote: >> [...] >>>> I am not sure about the implications of having >>>> pfn_valid()/pfn_present()/pfn_online() return true but accessing it >>>> results in crashes. (suspend, kdump, whatever other technology touches >>>> online memory) >>> >>> (oneidea: we could of course go ahead and mark the pages PG_offline >>> before unmapping the pfn range to work around these issues) >> >> PG_reserved and an elevated reference count should be enough to drive >> any pfn walker out. Pfn walkers shouldn't touch any page unless they >> know and recognize their type. > > Btw. this shouldn't be much different from DEBUG_PAGE_ALLOC in > principle. The memory is valid, but not mapped to the kernel virtual > space. Nobody should be really touching it anyway. > I guess that could work (I am happy with anything that gets rid of offline_pages()/device_online() here :D ). So for each node, alloc_contig_range() (if I remember correctly, all pages in the range have to be in the same zone), set them PG_reserved (+ maybe something else, we'll have to see). Then, unmap them. The reverse when freeing the memory. Guess this should leave the current user space interface unmodified. I can see that guard pages use a special page type (PageGuard), not sure if something like that is really required. We'll have to see. -- Thanks, David / dhildenb