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(p200300d82f221000d72dfd5f4118c70b.dip0.t-ipconnect.de. [2003:d8:2f22:1000:d72d:fd5f:4118:c70b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259d58f3sm9266294f8f.73.2025.02.16.02.32.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 16 Feb 2025 02:32:36 -0800 (PST) Message-ID: Date: Sun, 16 Feb 2025 11:32:34 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 4/8] mm/huge_memory: add buddy allocator like (non-uniform) folio_split() To: Zi Yan , linux-mm@kvack.org, Andrew Morton , "Kirill A . Shutemov" , "Matthew Wilcox (Oracle)" Cc: Ryan Roberts , Hugh Dickins , Yang Shi , Miaohe Lin , Kefeng Wang , Yu Zhao , John Hubbard , Baolin Wang , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250211155034.268962-1-ziy@nvidia.com> <20250211155034.268962-5-ziy@nvidia.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250211155034.268962-5-ziy@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11.02.25 16:50, Zi Yan wrote: > folio_split() splits a large folio in the same way as buddy allocator > splits a large free page for allocation. The purpose is to minimize the > number of folios after the split. For example, if user wants to free the > 3rd subpage in a order-9 folio, folio_split() will split the order-9 folio > as: > O-0, O-0, O-0, O-0, O-2, O-3, O-4, O-5, O-6, O-7, O-8 if it is anon, > since anon folio does not support order-1 yet. > ----------------------------------------------------------------- > | | | | | | | | | > |O-0|O-0|O-0|O-0| O-2 |...| O-7 | O-8 | > | | | | | | | | | > ----------------------------------------------------------------- > > O-1, O-0, O-0, O-2, O-3, O-4, O-5, O-6, O-7, O-9 if it is pagecache > --------------------------------------------------------------- > | | | | | | | | > | O-1 |O-0|O-0| O-2 |...| O-7 | O-8 | > | | | | | | | | > --------------------------------------------------------------- > > It generates fewer folios (i.e., 11 or 10) than existing page split > approach, which splits the order-9 to 512 order-0 folios. It also reduces > the number of new xa_node needed during a pagecache folio split from > 8 to 1, potentially decreasing the folio split failure rate due to memory > constraints. > > folio_split() and existing split_huge_page_to_list_to_order() share > the folio unmapping and remapping code in __folio_split() and the common > backend split code in __split_unmapped_folio() using > uniform_split variable to distinguish their operations. > > uniform_split_supported() and non_uniform_split_supported() are added > to factor out check code and will be used outside __folio_split() in the > following commit. > > Signed-off-by: Zi Yan > --- > mm/huge_memory.c | 137 ++++++++++++++++++++++++++++++++++------------- > 1 file changed, 100 insertions(+), 37 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 21ebe2dec5a4..400dfe8a6e60 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3853,12 +3853,68 @@ static int __split_unmapped_folio(struct folio *folio, int new_order, > return ret; > } > > +static bool non_uniform_split_supported(struct folio *folio, unsigned int new_order, > + bool warns) > +{ > + /* order-1 is not supported for anonymous THP. */ > + if (folio_test_anon(folio) && new_order == 1) { > + VM_WARN_ONCE(warns, "Cannot split to order-1 folio"); > + return false; > + } > + > + /* > + * No split if the file system does not support large folio. > + * Note that we might still have THPs in such mappings due to > + * CONFIG_READ_ONLY_THP_FOR_FS. But in that case, the mapping > + * does not actually support large folios properly. > + */ > + if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && > + !mapping_large_folio_support(folio->mapping)) { In this (and a similar case below), you need if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !folio_test_anon(folio) && !mapping_large_folio_support(folio->mapping)) { Otherwise mapping_large_folio_support() is unhappy: [root@localhost mm]# ./split_huge_page_test TAP version 13 1..20 ok 1 Split zero filled huge pages successful ok 2 Split huge pages to order 0 successful [ 144.936764][T15389] ------------[ cut here ]------------ [ 144.937948][T15389] Anonymous mapping always supports large folio [ 144.938164][T15389] WARNING: CPU: 5 PID: 15389 at ./include/linux/pagemap.h:494 uniform_split_supported+0x270/0x290 [ 144.941442][T15389] Modules linked in: [ 144.942212][T15389] CPU: 5 UID: 0 PID: 15389 Comm: split_huge_page Not tainted 6.14.0-rc2-00200-gdcbc194183fd #153 [ 144.944188][T15389] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014 [ 144.945934][T15389] RIP: 0010:uniform_split_supported+0x270/0x290 [ 144.947144][T15389] Code: ff 89 de e8 c2 20 ca ff 84 db 0f 85 47 fe ff ff e8 05 26 ca ff c6 05 f6 c2 22 06 01 90 48 c7 c7 18 44 fa 86 e8 31 2a ac ff 90 <0f> 0b 90 90 e9 24 fe ff ff e8 e2 25 ca ff 48 c7 c6 08 52 f7 86 48 [ 144.950897][T15389] RSP: 0018:ffffc90022813990 EFLAGS: 00010286 [ 144.952058][T15389] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8120ed77 [ 144.953559][T15389] RDX: ffff8881326f3880 RSI: ffffffff8120ed8a RDI: ffff8881326f3880 [ 144.955045][T15389] RBP: ffffea00062a0000 R08: 0000000000000001 R09: 0000000000000000 [ 144.956544][T15389] R10: 0000000000000000 R11: 0000000000000003 R12: 0000000000000001 [ 144.958043][T15389] R13: 0000000000000001 R14: ffff8881328b3951 R15: 0000000000000001 [ 144.959898][T15389] FS: 00007fb74cda4740(0000) GS:ffff888277b40000(0000) knlGS:0000000000000000 [ 144.961627][T15389] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 144.962886][T15389] CR2: 00007fb74ca00000 CR3: 000000013e072000 CR4: 0000000000750ef0 [ 144.964418][T15389] PKRU: 55555554 [ 144.965100][T15389] Call Trace: [ 144.965746][T15389] [ 144.966331][T15389] ? uniform_split_supported+0x270/0x290 -- Cheers, David / dhildenb