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[2003:cb:c710:8800:a73c:ec5b:c02c:5e0b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4215814f6c0sm44711195e9.46.2024.06.06.00.11.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Jun 2024 00:12:00 -0700 (PDT) Message-ID: <6c1fdc0a-98dd-47b5-933e-e2f6a91bc31f@redhat.com> Date: Thu, 6 Jun 2024 09:11:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/10] mm/ksm: skip subpages of compound pages To: Matthew Wilcox Cc: Alex Shi , alexs@kernel.org, Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, izik.eidus@ravellosystems.com, aarcange@redhat.com, chrisw@sous-sol.org, hughd@google.com References: <20240604042454.2012091-1-alexs@kernel.org> <20240604042454.2012091-3-alexs@kernel.org> <5bb3bbf6-6a22-449f-96f1-b9476357f284@gmail.com> <8a614d01-191e-45d1-b6b6-c36ec0bd9e5a@redhat.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: 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: rspam06 X-Rspamd-Queue-Id: 3B6824000F X-Stat-Signature: wmcnyu15c6aw811p4jg55ianrc673drj X-HE-Tag: 1717657925-848473 X-HE-Meta: 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 fbvzt2N1 N+o2Rg34SqCpUkCKJNJC4+3gW/BXVpYFbCZN9K4/oTZFUTgwR+UuB1QBf4llpZH6PW3gTPwu4ZRMYyc+YbNfcFterR/9ethJNb6pDPfjr5N9wMx06QccalH5bFjhHT/lL3m+wrilVC3RvgRqk9BtC5HdLrq/hudU/ePM03ANiwoL4cEh3VU5beDyxmWxel0j1WWjSgRI/EDW/kaYA9lkp0Vkq8VUR36ODwP2B5NxVUVQouZUFZhqoZrmxM/EEScIKiMCaYP79VlLx1jQVCnyJG71RZHmQUBZVEzxqphC8hrRr5TH0inh74PdEQPn7UUyIS1mwXS0wUhd+Z+dXqEjMh4lzDyOVCA96vD5Qlf5+mAjLbfKrezDTx5jPVBpxWOwyRo6rEZzGwk6dzHYZ1TG4wDokKNAaq2fc2mCrJDLt2WcR0fiLpUOwWfa+AjGpqqaadI8LwUpTd40hyNXRd6LJMhvreLgVHgacxEYn 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 05.06.24 23:12, Matthew Wilcox wrote: > On Wed, Jun 05, 2024 at 09:47:10AM +0200, David Hildenbrand wrote: >> On 05.06.24 08:14, Alex Shi wrote: >>> >>> >>> On 6/5/24 11:52 AM, Matthew Wilcox wrote: >>>> On Tue, Jun 04, 2024 at 12:24:44PM +0800, alexs@kernel.org wrote: >>>>> From: "Alex Shi (tencent)" >>>>> >>>>> When a folio isn't fit for KSM, the subpages are unlikely to be good, >>>>> So let's skip the rest page checking to save some actions. >>>> >>>> Why would you say that is true? We have plenty of evidence that >>>> userspace allocators can allocate large folios, then use only the first >>>> few bytes, leaving many tail pages full of zeroes. >>> >>> Um, that do need tail pages... >>> Is there some way to use more folio in ksm? >> >> My take, and Willy can correct me if I am wrong: >> >> "struct page" is not going to away any time soon, but it might shrink at >> some point. >> >> That is, we can use the "struct page" pointer to point at a page frame, and >> use "struct folio" to lookup/manage the metadata. > > Right. > >> That is, use "struct page" when accessing the actual memory content >> (checksum, testing for identical content), but use the folio part when >> looking up metadata (folio_test_anon() etc). In the future we might want to >> replace the "struct page" pointer by an index into the folio, but that >> doesn't have to happen right now. > > My current thinking is that folio->pfn is how we know where the memory > described by the folio is. Using an index would be memmap[folio->pfn + > index] which isn't terribly expensive, but we may as well pass around the > (folio, page) pair and save the reference to memmap. Right, as soon as the folio does not overlay the head page it's going to be a bit different. A (folio,page) pair, like we use in the RMAP code, is likely the best option for now and gives us sufficient flexibility for the future design. -- Cheers, David / dhildenb