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[209.132.183.28]) by mx.google.com with ESMTPS id x69si3136821qka.208.2019.02.27.23.38.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Feb 2019 23:38:37 -0800 (PST) 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-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 693E6C067C36; Thu, 28 Feb 2019 07:38:36 +0000 (UTC) Received: from [10.36.116.113] (ovpn-116-113.ams2.redhat.com [10.36.116.113]) by smtp.corp.redhat.com (Postfix) with ESMTP id 386EF619D5; Thu, 28 Feb 2019 07:38:35 +0000 (UTC) Subject: Re: [RFC PATCH] mm,memory_hotplug: Unlock 1GB-hugetlb on x86_64 To: Mike Kravetz , Oscar Salvador , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, mhocko@suse.com References: <20190221094212.16906-1-osalvador@suse.de> <20190227215109.cpiaheyqs2qdbl7p@d104.suse.de> <201cc8d8-953f-f198-bbfe-96470136db68@oracle.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <201cc8d8-953f-f198-bbfe-96470136db68@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 28 Feb 2019 07:38:36 +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 27.02.19 23:00, Mike Kravetz wrote: > On 2/27/19 1:51 PM, Oscar Salvador wrote: >> On Thu, Feb 21, 2019 at 10:42:12AM +0100, Oscar Salvador wrote: >>> [1] https://lore.kernel.org/patchwork/patch/998796/ >>> >>> Signed-off-by: Oscar Salvador >> >> Any further comments on this? >> I do have a "concern" I would like to sort out before dropping the RFC: >> >> It is the fact that unless we have spare gigantic pages in other notes, the >> offlining operation will loop forever (until the customer cancels the operation). >> While I do not really like that, I do think that memory offlining should be done >> with some sanity, and the administrator should know in advance if the system is going >> to be able to keep up with the memory pressure, aka: make sure we got what we need in >> order to make the offlining operation to succeed. >> That translates to be sure that we have spare gigantic pages and other nodes >> can take them. >> >> Given said that, another thing I thought about is that we could check if we have >> spare gigantic pages at has_unmovable_pages() time. >> Something like checking "h->free_huge_pages - h->resv_huge_pages > 0", and if it >> turns out that we do not have gigantic pages anywhere, just return as we have >> non-movable pages. > > Of course, that check would be racy. Even if there is an available gigantic > page at has_unmovable_pages() time there is no guarantee it will be there when > we want to allocate/use it. But, you would at least catch 'most' cases of > looping forever. > >> But I would rather not convulate has_unmovable_pages() with such checks and "trust" >> the administrator. I think we have the exact same issue already with huge/ordinary pages if we are low on memory. We could loop forever. In the long run, we should properly detect such issues and abort instead of looping forever I guess. But as we all know, error handling in the whole offlining part is still far away from being perfect ... -- Thanks, David / dhildenb