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=-10.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 36BF5C33CB1 for ; Mon, 27 Jan 2020 13:34:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 045AB20716 for ; Mon, 27 Jan 2020 13:34:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UJ93hWSN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728420AbgA0Ne1 (ORCPT ); Mon, 27 Jan 2020 08:34:27 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:44054 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726029AbgA0Ne1 (ORCPT ); Mon, 27 Jan 2020 08:34:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580132065; 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=TKAvTXVzm1MzDrmP8jUD3FXUmiynShS7FgS0aUVDSgw=; b=UJ93hWSNB7ubBoothoNoMVO4MAHsHwcIvOGHFasCQT9kTLV4CarI4Ii8OmMjHcpn+a7RXs m1JRkOd3MIJA89qnPU7FDyv1LdCgYh7qe7XeIk3qICixTR2CiieM8wJz6r+zdHZoEZEKg1 4BtbUFEatxDboVHQN64LbeOAYViz36g= 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-387-MseUeNKJMkq-ZhsoUYldkA-1; Mon, 27 Jan 2020 08:34:21 -0500 X-MC-Unique: MseUeNKJMkq-ZhsoUYldkA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1DAFC8010C5; Mon, 27 Jan 2020 13:34:19 +0000 (UTC) Received: from [10.36.118.65] (unknown [10.36.118.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id 214915C219; Mon, 27 Jan 2020 13:34:15 +0000 (UTC) Subject: Re: [PATCH RFC] drivers/base/memory.c: indicate all memory blocks as removable To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dan Williams , Greg Kroah-Hartman , "Rafael J. Wysocki" , Andrew Morton , powerpc-utils-devel@googlegroups.com, util-linux@vger.kernel.org, Badari Pulavarty , Nathan Fontenot , Robert Jennings , Heiko Carstens , Karel Zak References: <20200124155336.17126-1-david@redhat.com> <20200127132950.GH1183@dhcp22.suse.cz> 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: <548fbb8f-9c05-fbf7-4413-b48eeb7e1c8e@redhat.com> Date: Mon, 27 Jan 2020 14:34:15 +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: <20200127132950.GH1183@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: util-linux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: util-linux@vger.kernel.org On 27.01.20 14:29, Michal Hocko wrote: > On Fri 24-01-20 16:53:36, David Hildenbrand wrote: >> We see multiple issues with the implementation/interface to compute >> whether a memory block can be offlined (exposed via >> /sys/devices/system/memory/memoryX/removable) and would like to simplify >> it (remove the implementation). >> >> 1. It runs basically lockless. While this might be good for performance, >> we see possible races with memory offlining/unplug that will require >> at least some sort of locking to fix. >> >> 2. Nowadays, more false positives are possible. No arch-specific checks >> are performed that validate if memory offlining will not be denied >> right away (and such check will require locking). For example, arm64 >> won't allow to offline any memory block that was added during boot - >> which will imply a very high error rate. Other archs have other >> constraints. >> >> 3. The interface is inherently racy. E.g., if a memory block is >> detected to be removable (and was not a false positive at that time), >> there is still no guarantee that offlining will actually succeed. So >> any caller already has to deal with false positives. >> >> 4. It is unclear which performance benefit this interface actually >> provides. The introducing commit 5c755e9fd813 ("memory-hotplug: add >> sysfs removable attribute for hotplug memory remove") mentioned >> "A user-level agent must be able to identify which sections of >> memory are likely to be removable before attempting the >> potentially expensive operation." >> However, no actual performance comparison was included. >> >> Known users: >> - lsmem: Will group memory blocks based on the "removable" property. [1] >> - chmem: Indirect user. It has a RANGE mode where one can specify >> removable ranges identified via lsmem to be offlined. However, it >> also has a "SIZE" mode, which allows a sysadmin to skip the manual >> "identify removable blocks" step. [2] >> - powerpc-utils: Uses the "removable" attribute to skip some memory >> blocks right away when trying to find some to >> offline+remove. However, with ballooning enabled, it >> already skips this information completely (because it >> once resulted in many false negatives). Therefore, the >> implementation can deal with false positives properly >> already. [3] >> >> With CONFIG_MEMORY_HOTREMOVE, always indicating "removable" should not >> break any user space tool. We implement a very bad heuristic now. (in >> contrast: always returning "not removable" would at least affect >> powerpc-utils) >> >> Without CONFIG_MEMORY_HOTREMOVE we cannot offline anything, so report >> "not removable" as before. >> >> Original discussion can be found in [4] ("[PATCH RFC v1] mm: >> is_mem_section_removable() overhaul"). >> >> Other users of is_mem_section_removable() will be removed next, so that >> we can remove is_mem_section_removable() completely. >> >> [1] http://man7.org/linux/man-pages/man1/lsmem.1.html >> [2] http://man7.org/linux/man-pages/man8/chmem.8.html >> [3] https://github.com/ibm-power-utilities/powerpc-utils >> [4] https://lkml.kernel.org/r/20200117105759.27905-1-david@redhat.com >> >> Suggested-by: Michal Hocko >> Cc: Dan Williams >> Cc: Greg Kroah-Hartman >> Cc: "Rafael J. Wysocki" >> Cc: Andrew Morton >> Cc: powerpc-utils-devel@googlegroups.com >> Cc: util-linux@vger.kernel.org >> Cc: Badari Pulavarty >> Cc: Nathan Fontenot >> Cc: Robert Jennings >> Cc: Heiko Carstens >> Cc: Karel Zak >> Signed-off-by: David Hildenbrand > > Please add information provided by Nathan. > Acked-by: Michal Hocko > > Minor nit below. > >> +#ifdef CONFIG_MEMORY_HOTREMOVE >> + return sprintf(buf, "1\n"); >> +#else >> + return sprintf(buf, "0\n"); >> +#endif > int ret = IS_ENABLED(CONFIG_MEMORY_HOTREMOVE); > > return sprintf(buf, "%d\n", ret) > > would be slightly nicer than explicit ifdefs. > Indeed, thanks! -- Thanks, David / dhildenb