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=-2.5 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 F066AC5ACAE for ; Wed, 11 Sep 2019 13:03:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C4494206A1 for ; Wed, 11 Sep 2019 13:03:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728079AbfIKND7 (ORCPT ); Wed, 11 Sep 2019 09:03:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42242 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727976AbfIKND6 (ORCPT ); Wed, 11 Sep 2019 09:03:58 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A49701918654; Wed, 11 Sep 2019 13:03:57 +0000 (UTC) Received: from [10.36.117.155] (ovpn-117-155.ams2.redhat.com [10.36.117.155]) by smtp.corp.redhat.com (Postfix) with ESMTP id 389E75DC18; Wed, 11 Sep 2019 13:03:40 +0000 (UTC) Subject: Re: [PATCH v9 0/8] stg mail -e --version=v9 \ To: Michal Hocko Cc: "Michael S. Tsirkin" , Alexander Duyck , Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm list , Catalin Marinas , Dave Hansen , LKML , Matthew Wilcox , linux-mm , Andrew Morton , will@kernel.org, linux-arm-kernel@lists.infradead.org, Oscar Salvador , Yang Zhang , Pankaj Gupta , Konrad Rzeszutek Wilk , Nitesh Narayan Lal , Rik van Riel , lcapitulino@redhat.com, "Wang, Wei W" , Andrea Arcangeli , ying.huang@intel.com, Paolo Bonzini , Dan Williams , Fengguang Wu , "Kirill A. Shutemov" References: <20190910144713.GF2063@dhcp22.suse.cz> <20190910175213.GD4023@dhcp22.suse.cz> <1d7de9f9f4074f67c567dbb4cc1497503d739e30.camel@linux.intel.com> <20190911113619.GP4023@dhcp22.suse.cz> <20190911080804-mutt-send-email-mst@kernel.org> <20190911121941.GU4023@dhcp22.suse.cz> <20190911122526.GV4023@dhcp22.suse.cz> <4748a572-57b3-31da-0dde-30138e550c3a@redhat.com> <20190911125413.GY4023@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: <736594d6-b9ae-ddb9-2b96-85648728ef33@redhat.com> Date: Wed, 11 Sep 2019 15:03:39 +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: <20190911125413.GY4023@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Wed, 11 Sep 2019 13:03:58 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.09.19 14:54, Michal Hocko wrote: > On Wed 11-09-19 14:42:41, David Hildenbrand wrote: >> On 11.09.19 14:25, Michal Hocko wrote: >>> On Wed 11-09-19 14:19:41, Michal Hocko wrote: >>>> On Wed 11-09-19 08:08:38, Michael S. Tsirkin wrote: >>>>> On Wed, Sep 11, 2019 at 01:36:19PM +0200, Michal Hocko wrote: >>>>>> On Tue 10-09-19 14:23:40, Alexander Duyck wrote: >>>>>> [...] >>>>>>> We don't put any limitations on the allocator other then that it needs to >>>>>>> clean up the metadata on allocation, and that it cannot allocate a page >>>>>>> that is in the process of being reported since we pulled it from the >>>>>>> free_list. If the page is a "Reported" page then it decrements the >>>>>>> reported_pages count for the free_area and makes sure the page doesn't >>>>>>> exist in the "Boundary" array pointer value, if it does it moves the >>>>>>> "Boundary" since it is pulling the page. >>>>>> >>>>>> This is still a non-trivial limitation on the page allocation from an >>>>>> external code IMHO. I cannot give any explicit reason why an ordering on >>>>>> the free list might matter (well except for page shuffling which uses it >>>>>> to make physical memory pattern allocation more random) but the >>>>>> architecture seems hacky and dubious to be honest. It shoulds like the >>>>>> whole interface has been developed around a very particular and single >>>>>> purpose optimization. >>>>>> >>>>>> I remember that there was an attempt to report free memory that provided >>>>>> a callback mechanism [1], which was much less intrusive to the internals >>>>>> of the allocator yet it should provide a similar functionality. Did you >>>>>> see that approach? How does this compares to it? Or am I completely off >>>>>> when comparing them? >>>>>> >>>>>> [1] mostly likely not the latest version of the patchset >>>>>> http://lkml.kernel.org/r/1502940416-42944-5-git-send-email-wei.w.wang@intel.com >>>>> >>>>> Linus nacked that one. He thinks invoking callbacks with lots of >>>>> internal mm locks is too fragile. >>>> >>>> I would be really curious how much he would be happy about injecting >>>> other restrictions on the allocator like this patch proposes. This is >>>> more intrusive as it has a higher maintenance cost longterm IMHO. >>> >>> Btw. I do agree that callbacks with internal mm locks are not great >>> either. We do have a model for that in mmu_notifiers and it is something >>> I do consider PITA, on the other hand it is mostly sleepable part of the >>> interface which makes it the real pain. The above callback mechanism was >>> explicitly documented with restrictions and that the context is >>> essentially atomic with no access to particular struct pages and no >>> expensive operations possible. So in the end I've considered it >>> acceptably painful. Not that I want to override Linus' nack but if >>> virtualization usecases really require some form of reporting and no >>> other way to do that push people to invent even more interesting >>> approaches then we should simply give them/you something reasonable >>> and least intrusive to our internals. >>> >> >> The issue with "[PATCH v14 4/5] mm: support reporting free page blocks" >> is that it cannot really handle the use case we have here if I am not >> wrong. While a page is getting processed by the hypervisor (e.g. >> MADV_DONTNEED), it must not get reused. > > What prevents to use the callback to get a list of pfn ranges to work on > and then use something like start_isolate_page_range on the collected > pfn ranges to make sure nobody steals pages from under your feet, do > your thing and drop the isolated state afterwards. > > I am saying somethig like because you wouldn't really want a generic > has_unmovable_pages but rather > if (!page_ref_count(page)) { > if (PageBuddy(page)) > iter += (1 << page_order(page)) - 1; > continue; > } > subset of it. > Something slightly similar is being performed by Nitesh's patch set. On every free of a certain granularity, he records it in the bitmap. These bits are "hints of free pages". A thread then walks over the bitmap and tries to allocate the "hints". If the pages were already reused, the bit is silently cleared. Instead of allocating/freeing, we could only try to isolate the pageblock, then test if free. (One of the usual issues to work around is MAX_ORDER-1 crossing pageblocks, that might need special care) I think you should have a look at the rough idea of Nitesh's patch set to see if something like that is going into a better direction. The bitmap part is in place to do bulk reporting and avoid duplicate reports. I think main points we want (and what I am missing from callback idea being discussed) are 1. Do bulk reporting only when a certain threshold is reached 2. Report only bigger granularities (especially, avoid THP splits in the hypervisor - >= 2MB proofed to be effective) 3. Avoid reporting what has just been reported. 4. Continuously report, not the "one time report everything" approach. -- Thanks, David / dhildenb 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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 1A7C6C49ED6 for ; Wed, 11 Sep 2019 13:04:08 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E071C20863 for ; Wed, 11 Sep 2019 13:04:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="lA5WMp0Y" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E071C20863 Authentication-Results: mail.kernel.org; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190911125413.GY4023@dhcp22.suse.cz> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Wed, 11 Sep 2019 13:03:58 +0000 (UTC) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190911_060358_419405_0416A71F X-CRM114-Status: GOOD ( 29.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Yang Zhang , Pankaj Gupta , kvm list , "Michael S. Tsirkin" , Catalin Marinas , Alexander Duyck , lcapitulino@redhat.com, linux-mm , Alexander Duyck , will@kernel.org, Andrea Arcangeli , virtio-dev@lists.oasis-open.org, Rik van Riel , Matthew Wilcox , "Wang, Wei W" , ying.huang@intel.com, Konrad Rzeszutek Wilk , Dan Williams , linux-arm-kernel@lists.infradead.org, Oscar Salvador , Nitesh Narayan Lal , Dave Hansen , LKML , Paolo Bonzini , Andrew Morton , Fengguang Wu , "Kirill A. Shutemov" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 11.09.19 14:54, Michal Hocko wrote: > On Wed 11-09-19 14:42:41, David Hildenbrand wrote: >> On 11.09.19 14:25, Michal Hocko wrote: >>> On Wed 11-09-19 14:19:41, Michal Hocko wrote: >>>> On Wed 11-09-19 08:08:38, Michael S. Tsirkin wrote: >>>>> On Wed, Sep 11, 2019 at 01:36:19PM +0200, Michal Hocko wrote: >>>>>> On Tue 10-09-19 14:23:40, Alexander Duyck wrote: >>>>>> [...] >>>>>>> We don't put any limitations on the allocator other then that it needs to >>>>>>> clean up the metadata on allocation, and that it cannot allocate a page >>>>>>> that is in the process of being reported since we pulled it from the >>>>>>> free_list. If the page is a "Reported" page then it decrements the >>>>>>> reported_pages count for the free_area and makes sure the page doesn't >>>>>>> exist in the "Boundary" array pointer value, if it does it moves the >>>>>>> "Boundary" since it is pulling the page. >>>>>> >>>>>> This is still a non-trivial limitation on the page allocation from an >>>>>> external code IMHO. I cannot give any explicit reason why an ordering on >>>>>> the free list might matter (well except for page shuffling which uses it >>>>>> to make physical memory pattern allocation more random) but the >>>>>> architecture seems hacky and dubious to be honest. It shoulds like the >>>>>> whole interface has been developed around a very particular and single >>>>>> purpose optimization. >>>>>> >>>>>> I remember that there was an attempt to report free memory that provided >>>>>> a callback mechanism [1], which was much less intrusive to the internals >>>>>> of the allocator yet it should provide a similar functionality. Did you >>>>>> see that approach? How does this compares to it? Or am I completely off >>>>>> when comparing them? >>>>>> >>>>>> [1] mostly likely not the latest version of the patchset >>>>>> http://lkml.kernel.org/r/1502940416-42944-5-git-send-email-wei.w.wang@intel.com >>>>> >>>>> Linus nacked that one. He thinks invoking callbacks with lots of >>>>> internal mm locks is too fragile. >>>> >>>> I would be really curious how much he would be happy about injecting >>>> other restrictions on the allocator like this patch proposes. This is >>>> more intrusive as it has a higher maintenance cost longterm IMHO. >>> >>> Btw. I do agree that callbacks with internal mm locks are not great >>> either. We do have a model for that in mmu_notifiers and it is something >>> I do consider PITA, on the other hand it is mostly sleepable part of the >>> interface which makes it the real pain. The above callback mechanism was >>> explicitly documented with restrictions and that the context is >>> essentially atomic with no access to particular struct pages and no >>> expensive operations possible. So in the end I've considered it >>> acceptably painful. Not that I want to override Linus' nack but if >>> virtualization usecases really require some form of reporting and no >>> other way to do that push people to invent even more interesting >>> approaches then we should simply give them/you something reasonable >>> and least intrusive to our internals. >>> >> >> The issue with "[PATCH v14 4/5] mm: support reporting free page blocks" >> is that it cannot really handle the use case we have here if I am not >> wrong. While a page is getting processed by the hypervisor (e.g. >> MADV_DONTNEED), it must not get reused. > > What prevents to use the callback to get a list of pfn ranges to work on > and then use something like start_isolate_page_range on the collected > pfn ranges to make sure nobody steals pages from under your feet, do > your thing and drop the isolated state afterwards. > > I am saying somethig like because you wouldn't really want a generic > has_unmovable_pages but rather > if (!page_ref_count(page)) { > if (PageBuddy(page)) > iter += (1 << page_order(page)) - 1; > continue; > } > subset of it. > Something slightly similar is being performed by Nitesh's patch set. On every free of a certain granularity, he records it in the bitmap. These bits are "hints of free pages". A thread then walks over the bitmap and tries to allocate the "hints". If the pages were already reused, the bit is silently cleared. Instead of allocating/freeing, we could only try to isolate the pageblock, then test if free. (One of the usual issues to work around is MAX_ORDER-1 crossing pageblocks, that might need special care) I think you should have a look at the rough idea of Nitesh's patch set to see if something like that is going into a better direction. The bitmap part is in place to do bulk reporting and avoid duplicate reports. I think main points we want (and what I am missing from callback idea being discussed) are 1. Do bulk reporting only when a certain threshold is reached 2. Report only bigger granularities (especially, avoid THP splits in the hypervisor - >= 2MB proofed to be effective) 3. Avoid reporting what has just been reported. 4. Continuously report, not the "one time report everything" approach. -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-6118-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 99EDD985B47 for ; Wed, 11 Sep 2019 13:03:59 +0000 (UTC) References: <20190910144713.GF2063@dhcp22.suse.cz> <20190910175213.GD4023@dhcp22.suse.cz> <1d7de9f9f4074f67c567dbb4cc1497503d739e30.camel@linux.intel.com> <20190911113619.GP4023@dhcp22.suse.cz> <20190911080804-mutt-send-email-mst@kernel.org> <20190911121941.GU4023@dhcp22.suse.cz> <20190911122526.GV4023@dhcp22.suse.cz> <4748a572-57b3-31da-0dde-30138e550c3a@redhat.com> <20190911125413.GY4023@dhcp22.suse.cz> From: David Hildenbrand Message-ID: <736594d6-b9ae-ddb9-2b96-85648728ef33@redhat.com> Date: Wed, 11 Sep 2019 15:03:39 +0200 MIME-Version: 1.0 In-Reply-To: <20190911125413.GY4023@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: [virtio-dev] Re: [PATCH v9 0/8] stg mail -e --version=v9 \ To: Michal Hocko Cc: "Michael S. Tsirkin" , Alexander Duyck , Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm list , Catalin Marinas , Dave Hansen , LKML , Matthew Wilcox , linux-mm , Andrew Morton , will@kernel.org, linux-arm-kernel@lists.infradead.org, Oscar Salvador , Yang Zhang , Pankaj Gupta , Konrad Rzeszutek Wilk , Nitesh Narayan Lal , Rik van Riel , lcapitulino@redhat.com, "Wang, Wei W" , Andrea Arcangeli , ying.huang@intel.com, Paolo Bonzini , Dan Williams , Fengguang Wu , "Kirill A. Shutemov" List-ID: On 11.09.19 14:54, Michal Hocko wrote: > On Wed 11-09-19 14:42:41, David Hildenbrand wrote: >> On 11.09.19 14:25, Michal Hocko wrote: >>> On Wed 11-09-19 14:19:41, Michal Hocko wrote: >>>> On Wed 11-09-19 08:08:38, Michael S. Tsirkin wrote: >>>>> On Wed, Sep 11, 2019 at 01:36:19PM +0200, Michal Hocko wrote: >>>>>> On Tue 10-09-19 14:23:40, Alexander Duyck wrote: >>>>>> [...] >>>>>>> We don't put any limitations on the allocator other then that it needs to >>>>>>> clean up the metadata on allocation, and that it cannot allocate a page >>>>>>> that is in the process of being reported since we pulled it from the >>>>>>> free_list. If the page is a "Reported" page then it decrements the >>>>>>> reported_pages count for the free_area and makes sure the page doesn't >>>>>>> exist in the "Boundary" array pointer value, if it does it moves the >>>>>>> "Boundary" since it is pulling the page. >>>>>> >>>>>> This is still a non-trivial limitation on the page allocation from an >>>>>> external code IMHO. I cannot give any explicit reason why an ordering on >>>>>> the free list might matter (well except for page shuffling which uses it >>>>>> to make physical memory pattern allocation more random) but the >>>>>> architecture seems hacky and dubious to be honest. It shoulds like the >>>>>> whole interface has been developed around a very particular and single >>>>>> purpose optimization. >>>>>> >>>>>> I remember that there was an attempt to report free memory that provided >>>>>> a callback mechanism [1], which was much less intrusive to the internals >>>>>> of the allocator yet it should provide a similar functionality. Did you >>>>>> see that approach? How does this compares to it? Or am I completely off >>>>>> when comparing them? >>>>>> >>>>>> [1] mostly likely not the latest version of the patchset >>>>>> http://lkml.kernel.org/r/1502940416-42944-5-git-send-email-wei.w.wang@intel.com >>>>> >>>>> Linus nacked that one. He thinks invoking callbacks with lots of >>>>> internal mm locks is too fragile. >>>> >>>> I would be really curious how much he would be happy about injecting >>>> other restrictions on the allocator like this patch proposes. This is >>>> more intrusive as it has a higher maintenance cost longterm IMHO. >>> >>> Btw. I do agree that callbacks with internal mm locks are not great >>> either. We do have a model for that in mmu_notifiers and it is something >>> I do consider PITA, on the other hand it is mostly sleepable part of the >>> interface which makes it the real pain. The above callback mechanism was >>> explicitly documented with restrictions and that the context is >>> essentially atomic with no access to particular struct pages and no >>> expensive operations possible. So in the end I've considered it >>> acceptably painful. Not that I want to override Linus' nack but if >>> virtualization usecases really require some form of reporting and no >>> other way to do that push people to invent even more interesting >>> approaches then we should simply give them/you something reasonable >>> and least intrusive to our internals. >>> >> >> The issue with "[PATCH v14 4/5] mm: support reporting free page blocks" >> is that it cannot really handle the use case we have here if I am not >> wrong. While a page is getting processed by the hypervisor (e.g. >> MADV_DONTNEED), it must not get reused. > > What prevents to use the callback to get a list of pfn ranges to work on > and then use something like start_isolate_page_range on the collected > pfn ranges to make sure nobody steals pages from under your feet, do > your thing and drop the isolated state afterwards. > > I am saying somethig like because you wouldn't really want a generic > has_unmovable_pages but rather > if (!page_ref_count(page)) { > if (PageBuddy(page)) > iter += (1 << page_order(page)) - 1; > continue; > } > subset of it. > Something slightly similar is being performed by Nitesh's patch set. On every free of a certain granularity, he records it in the bitmap. These bits are "hints of free pages". A thread then walks over the bitmap and tries to allocate the "hints". If the pages were already reused, the bit is silently cleared. Instead of allocating/freeing, we could only try to isolate the pageblock, then test if free. (One of the usual issues to work around is MAX_ORDER-1 crossing pageblocks, that might need special care) I think you should have a look at the rough idea of Nitesh's patch set to see if something like that is going into a better direction. The bitmap part is in place to do bulk reporting and avoid duplicate reports. I think main points we want (and what I am missing from callback idea being discussed) are 1. Do bulk reporting only when a certain threshold is reached 2. Report only bigger granularities (especially, avoid THP splits in the hypervisor - >= 2MB proofed to be effective) 3. Avoid reporting what has just been reported. 4. Continuously report, not the "one time report everything" approach. -- Thanks, David / dhildenb --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org