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[209.132.183.28]) by mx.google.com with ESMTPS id y8si3438585qkj.369.2019.08.01.00.18.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Aug 2019 00:18:52 -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 0426BC04BD48; Thu, 1 Aug 2019 07:18:51 +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 6D6CC60623; Thu, 1 Aug 2019 07:18:48 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory To: Michal Hocko , Rashmica Gupta Cc: 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: <2ebfbd36-11bd-9576-e373-2964c458185b@redhat.com> <20190626080249.GA30863@linux> <2750c11a-524d-b248-060c-49e6b3eb8975@redhat.com> <20190626081516.GC30863@linux> <887b902e-063d-a857-d472-f6f69d954378@redhat.com> <9143f64391d11aa0f1988e78be9de7ff56e4b30b.camel@gmail.com> <20190702074806.GA26836@linux> <20190731120859.GJ9330@dhcp22.suse.cz> <4ddee0dd719abd50350f997b8089fa26f6004c0c.camel@gmail.com> <20190801071709.GE11627@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: <20190801071709.GE11627@dhcp22.suse.cz> 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 [10.5.110.31]); Thu, 01 Aug 2019 07:18:51 +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 09:17, Michal Hocko wrote: > On Thu 01-08-19 09:06:40, Rashmica Gupta wrote: >> On Wed, 2019-07-31 at 14:08 +0200, Michal Hocko wrote: >>> On Tue 02-07-19 18:52:01, Rashmica Gupta wrote: >>> [...] >>>>> 2) Why it was designed, what is the goal of the interface? >>>>> 3) When it is supposed to be used? >>>>> >>>>> >>>> There is a hardware debugging facility (htm) on some power chips. >>>> To use >>>> this you need a contiguous portion of memory for the output to be >>>> dumped >>>> to - and we obviously don't want this memory to be simultaneously >>>> used by >>>> the kernel. >>> >>> How much memory are we talking about here? Just curious. >> >> From what I've seen a couple of GB per node, so maybe 2-10GB total. > > OK, that is really a lot to keep around unused just in case the > debugging is going to be used. > > I am still not sure the current approach of (ab)using memory hotplug is > ideal. Sure there is some overlap but you shouldn't really need to > offline the required memory range at all. All you need is to isolate the > memory from any existing user and the page allocator. Have you checked > alloc_contig_range? > Rashmica mentioned somewhere in this thread that the virtual mapping must not be in place, otherwise the HW might prefetch some of this memory, leading to errors with memtrace (which checks that in HW). -- Thanks, David / dhildenb