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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 9887BC2D0DB for ; Fri, 24 Jan 2020 16:20:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6110B2087E for ; Fri, 24 Jan 2020 16:20:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NT9sfgD+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387985AbgAXQUd (ORCPT ); Fri, 24 Jan 2020 11:20:33 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:51353 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389697AbgAXQUa (ORCPT ); Fri, 24 Jan 2020 11:20:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579882828; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=brz54vRaQ0/yHXZ/qNT1DPv+N2eYASm4IBhoPhiL4CI=; b=NT9sfgD+KsW7p9il0wU2RFRClB8KNwnicu9RHlk6MNIG0Q3VkZCVOzTJHqXY5sc6EAxEMH +0mEiWN59P4M+NJJXymIXc4+LRcr5N26eTy8yyKPrqJ3ElE1Sk0mc9Olf8t+mL6pM2nE3F QMacV8kK47WKMv8RYsO/g1/Bltfk/ik= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-186-r2_ovX2VP0e4xPpNy3KAqA-1; Fri, 24 Jan 2020 11:20:24 -0500 X-MC-Unique: r2_ovX2VP0e4xPpNy3KAqA-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id D27BF186925C; Fri, 24 Jan 2020 16:20:20 +0000 (UTC) Received: from [10.36.116.39] (ovpn-116-39.ams2.redhat.com [10.36.116.39]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9785E10016E8; Fri, 24 Jan 2020 16:20:01 +0000 (UTC) Subject: Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting From: David Hildenbrand To: Alexander Graf , Alexander Duyck , kvm@vger.kernel.org, mst@redhat.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz Cc: yang.zhang.wz@gmail.com, nitesh@redhat.com, konrad.wilk@oracle.com, pagupta@redhat.com, riel@surriel.com, lcapitulino@redhat.com, dave.hansen@intel.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com, osalvador@suse.de, "Paterson-Jones, Roland" , hannes@cmpxchg.org, hare@suse.com References: <20200122173040.6142.39116.stgit@localhost.localdomain> <914aa4c3-c814-45e0-830b-02796b00b762@amazon.com> <0e2d04a8-af74-e2db-cab0-c67286e33a2a@redhat.com> <5d2daec8-985c-c0a4-4832-8e5493316306@amazon.com> <86dfc549-c5bc-e8b2-644d-4baceb8dc746@redhat.com> Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <811dbba2-f542-04da-1a7f-00c3785a39d0@redhat.com> Date: Fri, 24 Jan 2020 17:20:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <86dfc549-c5bc-e8b2-644d-4baceb8dc746@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24.01.20 14:25, David Hildenbrand wrote: > On 23.01.20 15:52, Alexander Graf wrote: >> >> >> On 23.01.20 15:05, David Hildenbrand wrote: >>> On 23.01.20 11:20, Alexander Graf wrote: >>>> Hi Alex, >>>> >>>> On 22.01.20 18:43, Alexander Duyck wrote: >>>>> This series provides an asynchronous means of reporting free guest pages >>>>> to a hypervisor so that the memory associated with those pages can be >>>>> dropped and reused by other processes and/or guests on the host. Using >>>>> this it is possible to avoid unnecessary I/O to disk and greatly improve >>>>> performance in the case of memory overcommit on the host. >>>>> >>>>> When enabled we will be performing a scan of free memory every 2 seconds >>>>> while pages of sufficiently high order are being freed. In each pass at >>>>> least one sixteenth of each free list will be reported. By doing this we >>>>> avoid racing against other threads that may be causing a high amount of >>>>> memory churn. >>>>> >>>>> The lowest page order currently scanned when reporting pages is >>>>> pageblock_order so that this feature will not interfere with the use of >>>>> Transparent Huge Pages in the case of virtualization. >>>>> >>>>> Currently this is only in use by virtio-balloon however there is the hope >>>>> that at some point in the future other hypervisors might be able to make >>>>> use of it. In the virtio-balloon/QEMU implementation the hypervisor is >>>>> currently using MADV_DONTNEED to indicate to the host kernel that the page >>>>> is currently free. It will be zeroed and faulted back into the guest the >>>>> next time the page is accessed. >>>>> >>>>> To track if a page is reported or not the Uptodate flag was repurposed and >>>>> used as a Reported flag for Buddy pages. We walk though the free list >>>>> isolating pages and adding them to the scatterlist until we either >>>>> encounter the end of the list, processed as many pages as were listed in >>>>> nr_free prior to us starting, or have filled the scatterlist with pages to >>>>> be reported. If we fill the scatterlist before we reach the end of the >>>>> list we rotate the list so that the first unreported page we encounter is >>>>> moved to the head of the list as that is where we will resume after we >>>>> have freed the reported pages back into the tail of the list. >>>>> >>>>> Below are the results from various benchmarks. I primarily focused on two >>>>> tests. The first is the will-it-scale/page_fault2 test, and the other is >>>>> a modified version of will-it-scale/page_fault1 that was enabled to use >>>>> THP. I did this as it allows for better visibility into different parts >>>>> of the memory subsystem. The guest is running with 32G for RAM on one >>>>> node of a E5-2630 v3. The host has had some features such as CPU turbo >>>>> disabled in the BIOS. >>>>> >>>>> Test page_fault1 (THP) page_fault2 >>>>> Name tasks Process Iter STDEV Process Iter STDEV >>>>> Baseline 1 1012402.50 0.14% 361855.25 0.81% >>>>> 16 8827457.25 0.09% 3282347.00 0.34% >>>>> >>>>> Patches Applied 1 1007897.00 0.23% 361887.00 0.26% >>>>> 16 8784741.75 0.39% 3240669.25 0.48% >>>>> >>>>> Patches Enabled 1 1010227.50 0.39% 359749.25 0.56% >>>>> 16 8756219.00 0.24% 3226608.75 0.97% >>>>> >>>>> Patches Enabled 1 1050982.00 4.26% 357966.25 0.14% >>>>> page shuffle 16 8672601.25 0.49% 3223177.75 0.40% >>>>> >>>>> Patches enabled 1 1003238.00 0.22% 360211.00 0.22% >>>>> shuffle w/ RFC 16 8767010.50 0.32% 3199874.00 0.71% >>>>> >>>>> The results above are for a baseline with a linux-next-20191219 kernel, >>>>> that kernel with this patch set applied but page reporting disabled in >>>>> virtio-balloon, the patches applied and page reporting fully enabled, the >>>>> patches enabled with page shuffling enabled, and the patches applied with >>>>> page shuffling enabled and an RFC patch that makes used of MADV_FREE in >>>>> QEMU. These results include the deviation seen between the average value >>>>> reported here versus the high and/or low value. I observed that during the >>>>> test memory usage for the first three tests never dropped whereas with the >>>>> patches fully enabled the VM would drop to using only a few GB of the >>>>> host's memory when switching from memhog to page fault tests. >>>>> >>>>> Any of the overhead visible with this patch set enabled seems due to page >>>>> faults caused by accessing the reported pages and the host zeroing the page >>>>> before giving it back to the guest. This overhead is much more visible when >>>>> using THP than with standard 4K pages. In addition page shuffling seemed to >>>>> increase the amount of faults generated due to an increase in memory churn. >>>>> The overhead is reduced when using MADV_FREE as we can avoid the extra >>>>> zeroing of the pages when they are reintroduced to the host, as can be seen >>>>> when the RFC is applied with shuffling enabled. >>>>> >>>>> The overall guest size is kept fairly small to only a few GB while the test >>>>> is running. If the host memory were oversubscribed this patch set should >>>>> result in a performance improvement as swapping memory in the host can be >>>>> avoided. >>>> >>>> >>>> I really like the approach overall. Voluntarily propagating free memory >>>> from a guest to the host has been a sore point ever since KVM was >>>> around. This solution looks like a very elegant way to do so. >>>> >>>> The big piece I'm missing is the page cache. Linux will by default try >>>> to keep the free list as small as it can in favor of page cache, so most >>>> of the benefit of this patch set will be void in real world scenarios. >>> >>> One approach is to move (parts of) the page cache from the guest to the >>> hypervisor - e.g., using emulated NVDIMM or virtio-pmem. >> >> Whether you can do that depends heavily on your virtualization >> environment. On a host with single tenant VMs, that's definitely >> feasible. In a Kubernetes environment, it might also be feasible. > > I would be interesting in which environments this is an actual problem > that can't be solved in the hypervisor (e.g., see below). Okay, as Alex told me offline, (somewhat obvious) environments are where the hypervisor page cache is not involved (e.g., vfio etc.) -- Thanks, David / dhildenb