Received: by 2002:a25:c205:0:0:0:0:0 with SMTP id s5csp2321753ybf; Mon, 2 Mar 2020 06:24:17 -0800 (PST) X-Google-Smtp-Source: APXvYqxE9d+YO/IiOfGG/T+xfo7hXS2UIhwljDQD4WpX5bDtnuQgZqa8OgT4mmTE/EHQCGRnmOFk X-Received: by 2002:aca:4843:: with SMTP id v64mr11236343oia.13.1583159056956; Mon, 02 Mar 2020 06:24:16 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1583159056; cv=none; d=google.com; s=arc-20160816; b=eP6R/y4xRfcXsGr9uOM8PB09QA4pWrmVDk+fbydY3dpndvxtqsGieHgAx1pTZtgMIt XZNSRunJ33zK8uNmxfm59PBqRd75mLAVyDX73i7hfcS4oZEkmpyOWvZMVDoa0vR1Ol4a bbQVU31EkTX5XAksu8SzeDCYc+HB5F4cKRypEjjEpEaj+lpVPbiy6YMr3riXPmaI4e+x +VY8owLtAWkFL3oaVAiNbYidOuJSAlghIhYW+/4l0nSDGJwzbqaCKQ+HgCjz7iyM/51Y bKK0J13z2JuzoVFXEr/jD94qtOdnIfNaItmLrMahoE4Tga6KHozpaslxufz0R/MQH6l7 6nQQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding :content-language:in-reply-to:mime-version:user-agent:date :message-id:organization:autocrypt:from:references:cc:to:subject :dkim-signature; bh=qzHi0fYePwF5PDGy1PMUYXlkuJi/8ZgjqOT16BelPC4=; b=mBFCWC+Df6nkDy97c8sLqc1hqilBIWxJ5UwZ9pDNH4ACyfjRZuABUGG1Sn2QpmnR35 dOt76Xhq8HWCzqEbgS+eXKoWS3n1EuPdAS4byEIQMGSzTeEDwICDnODSLnE6zdbu+RlP rtVFJv8cEBBcqu/C5ot5RiU69hskAiKeCuCnfrSUDjGqqDxxiakzxjiUPS5a/KHOwvU2 7cx+bzVZilIEstEEELE93WzrQA/21ZDVwDjGBvXUWxrTq3Ka289NOKyoc91/PBeBGu6n RxUjR56Kf7EM8Sv8R+aZoeWZXJ3WgTCF6xGMLeNYUprCzsesMPSSTUhCnREh+nQSemUT +pYQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=aApkJ8Xr; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id z21si6392730oti.199.2020.03.02.06.24.04; Mon, 02 Mar 2020 06:24:16 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=aApkJ8Xr; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727231AbgCBOXa (ORCPT + 99 others); Mon, 2 Mar 2020 09:23:30 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:60970 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726969AbgCBOX3 (ORCPT ); Mon, 2 Mar 2020 09:23:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583159008; 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=qzHi0fYePwF5PDGy1PMUYXlkuJi/8ZgjqOT16BelPC4=; b=aApkJ8XrgRU7fVPkhQmugZTxSXCvfq6321onF46D509UlnO/rMxnFLZ2sOL/WlHyIdMH+9 dk2iSo1+USAySIS6MDKYCauIQoej4uzq4TLbu5pg8yiOU9IEpm59yaVHcLR6LeSQMZAH2j bYfNWE48IlzvJv0nvYEg3ZIJ17VgNsA= 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-416-EoTnE-xIPnOj9K6Jmttt1w-1; Mon, 02 Mar 2020 09:23:26 -0500 X-MC-Unique: EoTnE-xIPnOj9K6Jmttt1w-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 22EDC801E76; Mon, 2 Mar 2020 14:23:24 +0000 (UTC) Received: from [10.36.116.114] (ovpn-116-114.ams2.redhat.com [10.36.116.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2647661069; Mon, 2 Mar 2020 14:23:17 +0000 (UTC) Subject: Re: [RFC 0/3] mm: Discard lazily freed pages when migrating To: "Huang, Ying" , Michal Hocko Cc: Matthew Wilcox , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Vlastimil Babka , Zi Yan , Peter Zijlstra , Dave Hansen , Minchan Kim , Johannes Weiner , Hugh Dickins , Alexander Duyck References: <20200228033819.3857058-1-ying.huang@intel.com> <20200228034248.GE29971@bombadil.infradead.org> <87a7538977.fsf@yhuang-dev.intel.com> <871rqf850z.fsf@yhuang-dev.intel.com> <20200228095048.GK3771@dhcp22.suse.cz> <87d09u7sm2.fsf@yhuang-dev.intel.com> From: David Hildenbrand 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: <8005e5a1-e2f2-1e57-ccb4-0cb9371b080d@redhat.com> Date: Mon, 2 Mar 2020 15:23:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <87d09u7sm2.fsf@yhuang-dev.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02.03.20 15:12, Huang, Ying wrote: > Michal Hocko writes: > >> On Fri 28-02-20 16:55:40, Huang, Ying wrote: >>> David Hildenbrand writes: >> [...] >>>> E.g., free page reporting in QEMU wants to use MADV_FREE. The guest will >>>> report currently free pages to the hypervisor, which will MADV_FREE the >>>> reported memory. As long as there is no memory pressure, there is no >>>> need to actually free the pages. Once the guest reuses such a page, it >>>> could happen that there is still the old page and pulling in in a fresh >>>> (zeroed) page can be avoided. >>>> >>>> AFAIKs, after your change, we would get more pages discarded from our >>>> guest, resulting in more fresh (zeroed) pages having to be pulled in >>>> when a guest touches a reported free page again. But OTOH, page >>>> migration is speed up (avoiding to migrate these pages). >>> >>> Let's look at this problem in another perspective. To migrate the >>> MADV_FREE pages of the QEMU process from the node A to the node B, we >>> need to free the original pages in the node A, and (maybe) allocate the >>> same number of pages in the node B. So the question becomes >>> >>> - we may need to allocate some pages in the node B >>> - these pages may be accessed by the application or not >>> - we should allocate all these pages in advance or allocate them lazily >>> when they are accessed. >>> >>> We thought the common philosophy in Linux kernel is to allocate lazily. >> >> The common philosophy is to cache as much as possible. > > Yes. This is another common philosophy. And MADV_FREE pages is > different from caches such as the page caches because it has no valid > contents. Side note: It might contain valid content until discarded/zeroed out. E.g., an application could use a marker bit (e.g., first bit) to detect if the page still contains valid data or not. If the data is still marked valid, the content could be reuse immediately. Not sure if there is any such application, though :) -- Thanks, David / dhildenb