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Shutemov" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Michal Hocko , Oscar Salvador References: <0B77E39C-BD38-4A61-AB28-3578B519952F@redhat.com> <20200114104119.pybggnb4b2mq45wr@box> 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: <4de17591-e2c4-daff-e4b2-d03dd8792d0f@redhat.com> Date: Tue, 14 Jan 2020 11:49:19 +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: <20200114104119.pybggnb4b2mq45wr@box> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 14.01.20 11:41, Kirill A. Shutemov wrote: > On Tue, Jan 14, 2020 at 12:02:00AM +0100, David Hildenbrand wrote: >> >> >>> Am 13.01.2020 um 23:57 schrieb David Hildenbrand : >>> >>> =EF=BB=BF >>> >>>>> Am 13.01.2020 um 23:41 schrieb Kirill A. Shutemov : >>>>> >>>>> =EF=BB=BFOn Mon, Jan 13, 2020 at 03:40:35PM +0100, David Hildenbran= d wrote: >>>>> Let's move it to the header and use the shorter variant from >>>>> mm/page_alloc.c (the original one will also check >>>>> "__highest_present_section_nr + 1", which is not necessary). While = at it, >>>>> make the section_nr in next_pfn() const. >>>>> >>>>> In next_pfn(), we now return section_nr_to_pfn(-1) instead of -1 on= ce >>>>> we exceed __highest_present_section_nr, which doesn't make a differ= ence in >>>>> the caller as it is big enough (>=3D all sane end_pfn). >>>>> >>>>> Cc: Andrew Morton >>>>> Cc: Michal Hocko >>>>> Cc: Oscar Salvador >>>>> Cc: Kirill A. Shutemov >>>>> Signed-off-by: David Hildenbrand >>>>> --- >>>>> include/linux/mmzone.h | 10 ++++++++++ >>>>> mm/page_alloc.c | 11 ++--------- >>>>> mm/sparse.c | 10 ---------- >>>>> 3 files changed, 12 insertions(+), 19 deletions(-) >>>>> >>>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>>>> index c2bc309d1634..462f6873905a 100644 >>>>> --- a/include/linux/mmzone.h >>>>> +++ b/include/linux/mmzone.h >>>>> @@ -1379,6 +1379,16 @@ static inline int pfn_present(unsigned long = pfn) >>>>> return present_section(__nr_to_section(pfn_to_section_nr(pfn))); >>>>> } >>>>> >>>>> +static inline unsigned long next_present_section_nr(unsigned long = section_nr) >>>>> +{ >>>>> + while (++section_nr <=3D __highest_present_section_nr) { >>>>> + if (present_section_nr(section_nr)) >>>>> + return section_nr; >>>>> + } >>>>> + >>>>> + return -1; >>>>> +} >>>>> + >>>>> /* >>>>> * These are _only_ used during initialisation, therefore they >>>>> * can use __initdata ... They could have names to indicate >>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>>> index a92791512077..26e8044e9848 100644 >>>>> --- a/mm/page_alloc.c >>>>> +++ b/mm/page_alloc.c >>>>> @@ -5852,18 +5852,11 @@ overlap_memmap_init(unsigned long zone, uns= igned long *pfn) >>>>> /* Skip PFNs that belong to non-present sections */ >>>>> static inline __meminit unsigned long next_pfn(unsigned long pfn) >>>>> { >>>>> - unsigned long section_nr; >>>>> + const unsigned long section_nr =3D pfn_to_section_nr(++pfn); >>>>> >>>>> - section_nr =3D pfn_to_section_nr(++pfn); >>>>> if (present_section_nr(section_nr)) >>>>> return pfn; >>>>> - >>>>> - while (++section_nr <=3D __highest_present_section_nr) { >>>>> - if (present_section_nr(section_nr)) >>>>> - return section_nr_to_pfn(section_nr); >>>>> - } >>>>> - >>>>> - return -1; >>>>> + return section_nr_to_pfn(next_present_section_nr(section_nr)); >>>> >>>> This changes behaviour in the corner case: if next_present_section_n= r() >>>> returns -1, we call section_nr_to_pfn() for it. It's unlikely would = give >>>> any valid pfn, but I can't say for sure for all archs. I guess the w= orst >>>> case scenrio would be endless loop over the same secitons/pfns. >>>> >>>> Have you considered the case? >>> >>> Yes, see the patch description. We return -1 << PFN_SECTION_SHIFT, so= a number close to the end of the address space (0xfff...000). (Will doub= le check tomorrow if any 32bit arch could be problematic here) >> >> ... but thinking again, 0xfff... is certainly an invalid PFN, so this = should work just fine. >> >> (biggest possible pfn is -1 >> PFN_SHIFT) >> >> But it=E2=80=98s late in Germany, will double check tomorrow :) >=20 > If the end_pfn happens the be more than -1UL << PFN_SECTION_SHIFT we ar= e > screwed: the pfn is invalid, next_present_section_nr() returns -1, the > next iterartion is on the same pfn and we have endless loop. >=20 > The question is whether we can prove end_pfn is always less than > -1UL << PFN_SECTION_SHIFT in any configuration of any arch. >=20 > It is not obvious for me. memmap_init_zone() is called for a physical memory region: pfn + size (nr_pages) The highest possible PFN you can have is "-1(unsigned long) >> PFN_SHIFT". So even if you would want to add the very last section, the PFN would still be smaller than -1UL << PFN_SECTION_SHIFT. --=20 Thanks, David / dhildenb