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Mon, 13 Jan 2020 15:01:46 +0000 (UTC) Received: from [10.36.117.201] (ovpn-117-201.ams2.redhat.com [10.36.117.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id 711095DA70; Mon, 13 Jan 2020 15:01:43 +0000 (UTC) Subject: Re: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose is_mem_section_removable() symbol To: Tianyu Lan , Michal Hocko , "lantianyu1986@gmail.com" Cc: KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "sashal@kernel.org" , "akpm@linux-foundation.org" , Michael Kelley , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , vkuznets , "eric.devolder@oracle.com" , "vbabka@suse.cz" , "osalvador@suse.de" , Pasha Tatashin , "rppt@linux.ibm.com" References: <20200107130950.2983-1-Tianyu.Lan@microsoft.com> <20200107130950.2983-3-Tianyu.Lan@microsoft.com> <20200107133623.GJ32178@dhcp22.suse.cz> <99a6db0c-6d73-d982-58b3-7a0172748ae4@redhat.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: Date: Mon, 13 Jan 2020 16:01:42 +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: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13.01.20 15:49, Tianyu Lan wrote: >> From: David Hildenbrand >> Sent: Friday, January 10, 2020 9:42 PM >> To: Michal Hocko ; lantianyu1986@gmail.com >> Cc: KY Srinivasan ; Haiyang Zhang >> ; Stephen Hemminger ; >> sashal@kernel.org; akpm@linux-foundation.org; Michael Kelley >> ; Tianyu Lan ; linux= - >> hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; linux-mm@kvack.o= rg; >> vkuznets ; eric.devolder@oracle.com; vbabka@suse.= cz; >> osalvador@suse.de; Pasha Tatashin ; >> rppt@linux.ibm.com >> Subject: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose >> is_mem_section_removable() symbol >> >> On 07.01.20 14:36, Michal Hocko wrote: >>> On Tue 07-01-20 21:09:42, lantianyu1986@gmail.com wrote: >>>> From: Tianyu Lan >>>> >>>> Hyper-V balloon driver will use is_mem_section_removable() to check >>>> whether memory block is removable or not when receive memory hot >>>> remove msg. Expose it. >>> >>> I do not think this is a good idea. The check is inherently racy. Why >>> cannot the balloon driver simply hotremove the region when asked? >>> >> >> It's not only racy, it also gives no guarantees. False postives and fa= lse negatives >> are possible. >> >> If you want to avoid having to loop forever trying to offline when cal= ling >> offline_and_remove_memory(), you could try to >> alloc_contig_range() the memory first and then play the PG_offline+not= ifier >> game like virtio-mem. >> >> I don't remember clearly, but I think pinned pages can make offlining = loop for a >> long time. And I remember there were other scenarios as well (includin= g out of >> memory conditions and similar). >> >> I sent an RFC [1] for powerpc/memtrace that does the same (just error >> handling is more complicated as it wants to offline and remove multipl= e >> consecutive memory blocks) - if you want to try to go down that path. >> > Hi David & Michal: > Thanks for your review. Some memory blocks are not suitable for hot-pl= ug. > If not check memory block's removable, offline_pages() will report some= failure error > e.g, "failed due to memory holes" and "failure to isolate range". I th= ink the check maybe > added into offline_and_remove_memory()? This may help to not create/exp= ose a new > interface to do such check in module. So it's all about the logging output. Duplicating these checks feels very wrong. And you will still get plenty of page dumps (read below), so that won't help. We have pr_debug() for these "failure ..." message. that should therefore not be an issue on production systems, right? However, you will see dump_page()s quite often, which logs via pr_warn(). Of course, we could add a mechanism to temporarily disable logging output for these call paths, but it might actually be helpful for debugging. We might just want to convert everything that is not actually a warning to pr_debug() - especially in dump_page(). --=20 Thanks, David / dhildenb