From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1F90DC3A5A6 for ; Mon, 23 Sep 2019 09:31:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C75E620673 for ; Mon, 23 Sep 2019 09:31:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C75E620673 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 299A86B0007; Mon, 23 Sep 2019 05:31:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 24A7D6B0008; Mon, 23 Sep 2019 05:31:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 13A0F6B000A; Mon, 23 Sep 2019 05:31:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id E73CA6B0007 for ; Mon, 23 Sep 2019 05:31:38 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 956A7A2C0 for ; Mon, 23 Sep 2019 09:31:38 +0000 (UTC) X-FDA: 75965667876.11.wood32_e314f3362336 X-HE-Tag: wood32_e314f3362336 X-Filterd-Recvd-Size: 8807 Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Mon, 23 Sep 2019 09:31:37 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F3D2CA26685; Mon, 23 Sep 2019 09:31:35 +0000 (UTC) Received: from [10.36.116.207] (ovpn-116-207.ams2.redhat.com [10.36.116.207]) by smtp.corp.redhat.com (Postfix) with ESMTP id BAFD31001B11; Mon, 23 Sep 2019 09:31:31 +0000 (UTC) Subject: Re: [PATCH v1 0/3] mm/memory_hotplug: Export generic_online_page() To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Souptick Joarder , linux-hyperv@vger.kernel.org, Andrew Morton , Dan Williams , Haiyang Zhang , "K. Y. Srinivasan" , Oscar Salvador , Pavel Tatashin , Qian Cai , Sasha Levin , Stephen Hemminger , Wei Yang References: <20190909114830.662-1-david@redhat.com> <20190923085807.GD6016@dhcp22.suse.cz> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: Date: Mon, 23 Sep 2019 11:31:30 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190923085807.GD6016@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.68]); Mon, 23 Sep 2019 09:31:36 +0000 (UTC) Content-Transfer-Encoding: quoted-printable 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 23.09.19 10:58, Michal Hocko wrote: > On Fri 20-09-19 10:17:54, David Hildenbrand wrote: >> On 09.09.19 13:48, David Hildenbrand wrote: >>> Based on linux/next + "[PATCH 0/3] Remove __online_page_set_limits()" >>> >>> Let's replace the __online_page...() functions by generic_online_page= (). >>> Hyper-V only wants to delay the actual onlining of un-backed pages, s= o we >>> can simpy re-use the generic function. >>> >>> Only compile-tested. >>> >>> Cc: Souptick Joarder >>> >>> David Hildenbrand (3): >>> mm/memory_hotplug: Export generic_online_page() >>> hv_balloon: Use generic_online_page() >>> mm/memory_hotplug: Remove __online_page_free() and >>> __online_page_increment_counters() >>> >>> drivers/hv/hv_balloon.c | 3 +-- >>> include/linux/memory_hotplug.h | 4 +--- >>> mm/memory_hotplug.c | 17 ++--------------- >>> 3 files changed, 4 insertions(+), 20 deletions(-) >>> >> >> Ping, any comments on this one? >=20 > Unification makes a lot of sense to me. You can add > Acked-by: Michal Hocko >=20 > I will most likely won't surprise if I asked for more here though ;) I'm not surprised, but definitely not in a negative sense ;) I was asking myself if we could somehow rework this, too. > I have to confess I really detest the whole concept of a hidden callbac= k > with a very weird API. Is this something we can do about? I do realize > that adding a callback would require either cluttering the existing API= s > but maybe we can come up with something more clever. Or maybe existing > external users of online callback can do that as a separate step after > the online is completed - or is this impossible due to locking > guarantees? >=20 The use case of this (somewhat special) callback really is to avoid selected (unbacked in the hypervisor) pages to get put to the buddy just now, but instead to defer that (sometimes, defer till infinity ;) ). Especially, to hinder these pages from getting touched at all. Pages that won't be put to the buddy will usually get PG_offline set (e.g., Hyper-V and XEN) - the only two users I am aware of. For Hyper-V (and also eventually virtio-mem), it is important to set PG_offline before marking the section to be online (SECTION_IS_ONLINE). Only this way, PG_offline is properly set on all pfn_to_online_page() pages, meaning "don't touch this page" - e.g., used to skip over such pages when suspending or by makedumpfile to skip over such offline pages when creating a memory dump. So if we would e.g., try to piggy-back onto the memory_notify() infrastructure, we could 1. Online all pages to the buddy (dropping the callback) 2. E.g., memory_notify(MEM_ONLINE_PAGES, &arg); -> in the notifier, pull pages from the buddy, mark sections online 3. Set all involved sections online (online_mem_sections()) However, I am not sure what actually happens after 1. - we are only holding the device hotplug lock and the memory hotplug lock, so the pages can just get allocated. Also, it sounds like more work and code for the same end result (okay, if the rework is really necessary, though)= . So yeah, while the current callback might not be optimal, I don't see an easy and clean way to rework this. With the change in this series we are at least able to simply defer doing what would have been done without the callback - not perfect but better. Do you have anything in mind that could work out and make this nicer? --=20 Thanks, David / dhildenb