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[2003:cb:c70c:3c00:686e:317c:3ed4:d7b8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42100fb8f4asm216961205e9.41.2024.05.29.08.58.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 May 2024 08:58:05 -0700 (PDT) Message-ID: <3771cb2d-932f-49ee-aac2-e67206b94ebe@redhat.com> Date: Wed, 29 May 2024 17:58:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 26] mm allow reuse of the lower 16 bit of the page type with an actual type To: wang wei Cc: 42.hyeyoo@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, minchan@kernel.org, rppt@kernel.org, senozhatsky@chromium.org, willy@infradead.org References: <20240527141454.113132-3-david@redhat.com> <20240529155520.33161-1-a929244872@163.com> From: David Hildenbrand 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: <20240529155520.33161-1-a929244872@163.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 365ECA0008 X-Stat-Signature: 1d3t5wo4p5zqjpupunns1uo5yruzry4o X-HE-Tag: 1716998290-144646 X-HE-Meta: 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 v4f1CgBp 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 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: List-Subscribe: List-Unsubscribe: On 29.05.24 17:55, wang wei wrote: > --- >> As long as the owner sets a page type first, we can allow reuse of the >> lower 18 bit: sufficient to store an offset into a 64 KiB page, which >> is the maximum base page size in *common* configurations (ignoring the >> 256 KiB variant). Restrict it to the head page. >> >> We'll use that for zsmalloc next, to set a proper type while still >> reusing that field to store information (offset into a base page) that >> cannot go elsewhere for now. >> >> Fear of running out of bits for storing the actual type? Actually, we >> don't need one bit per type, we could store a single value instead. >> Further, we could likely limit PAGE_TYPE_BASE to a single (highest) bit. >> >> Signed-off-by: David Hildenbrand >> --- >> include/linux/mm_types.h | 5 +++++ >> include/linux/page-flags.h | 20 ++++++++++++-------- >> 2 files changed, 17 insertions(+), 8 deletions(-) >> >> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h >> index 6b2aeba792c4..598cfedbbfa0 100644 >> --- a/include/linux/mm_types.h >> +++ b/include/linux/mm_types.h >> @@ -157,6 +157,11 @@ struct page { >> * >> * See page-flags.h for a list of page types which are currently >> * stored here. >> + * >> + * Owners of typed folios may reuse the lower 16 bit of the >> + * head page page_type field after setting the page type, >> + * but must reset these 16 bit to -1 before clearing the >> + * page type. >> */ >> unsigned int page_type; >> >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index 104078afe0b1..b43e380ffa0b 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h >> @@ -945,14 +945,18 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) >> */ >> >> #define PAGE_TYPE_BASE 0xf0000000 >> -/* Reserve 0x0000007f to catch underflows of _mapcount */ >> -#define PAGE_MAPCOUNT_RESERVE -128 >> -#define PG_buddy 0x00000080 >> -#define PG_offline 0x00000100 >> -#define PG_table 0x00000200 >> -#define PG_guard 0x00000400 >> -#define PG_hugetlb 0x00000800 >> -#define PG_slab 0x00001000 >> +/* >> + * Reserve 0x0000ffff to catch underflows of _mapcount and >> + * allow owners that set a type to reuse the lower 16 bit for their own >> + * purposes. >> + */ >> +#define PAGE_MAPCOUNT_RESERVE -65536 >> +#define PG_buddy 0x00010000 >> +#define PG_offline 0x00020000 >> +#define PG_table 0x00040000 >> +#define PG_guard 0x00080000 >> +#define PG_hugetlb 0x00100800 > > Every PG_XX occupies one bit in my understanding. But why PG_hugetlb occupies two bits? Because it's wrong (although not harmful). Same issue in v2, fat fingers. Thanks for pointing that out! -- Cheers, David / dhildenb