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(p200300cbc7302200722983b1524e283a.dip0.t-ipconnect.de. [2003:cb:c730:2200:7229:83b1:524e:283a]) by smtp.gmail.com with ESMTPSA id jj19-20020a05600c6a1300b0040fccf7e8easm9024482wmb.36.2024.02.12.08.27.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Feb 2024 08:28:00 -0800 (PST) Message-ID: Date: Mon, 12 Feb 2024 17:27:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 22/25] mm: Add pte_batch_hint() to reduce scanning in folio_pte_batch() To: Ryan Roberts , Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , Mark Rutland , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Cc: linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240202080756.1453939-1-ryan.roberts@arm.com> <20240202080756.1453939-23-ryan.roberts@arm.com> <6d452a1a-1edc-4e97-8b39-99dc48315bb8@redhat.com> <82c59a7f-328e-4521-8855-ccacc3dc4ce5@arm.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: <82c59a7f-328e-4521-8855-ccacc3dc4ce5@arm.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: 8bit X-Rspamd-Queue-Id: 1A5491C0007 X-Rspam-User: X-Stat-Signature: jrbezq1wycsundiur8c6ka5jeysdmu7y X-Rspamd-Server: rspam03 X-HE-Tag: 1707755286-926111 X-HE-Meta: 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 rCpP2vy1 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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 12.02.24 16:47, Ryan Roberts wrote: > On 12/02/2024 13:43, David Hildenbrand wrote: >> On 02.02.24 09:07, Ryan Roberts wrote: >>> Some architectures (e.g. arm64) can tell from looking at a pte, if some >>> follow-on ptes also map contiguous physical memory with the same pgprot. >>> (for arm64, these are contpte mappings). >>> >>> Take advantage of this knowledge to optimize folio_pte_batch() so that >>> it can skip these ptes when scanning to create a batch. By default, if >>> an arch does not opt-in, folio_pte_batch() returns a compile-time 1, so >>> the changes are optimized out and the behaviour is as before. >>> >>> arm64 will opt-in to providing this hint in the next patch, which will >>> greatly reduce the cost of ptep_get() when scanning a range of contptes. >>> >>> Tested-by: John Hubbard >>> Signed-off-by: Ryan Roberts >>> --- >>>   include/linux/pgtable.h | 18 ++++++++++++++++++ >>>   mm/memory.c             | 20 +++++++++++++------- >>>   2 files changed, 31 insertions(+), 7 deletions(-) >>> >>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >>> index 50f32cccbd92..cba31f177d27 100644 >>> --- a/include/linux/pgtable.h >>> +++ b/include/linux/pgtable.h >>> @@ -212,6 +212,24 @@ static inline int pmd_dirty(pmd_t pmd) >>>   #define arch_flush_lazy_mmu_mode()    do {} while (0) >>>   #endif >>>   +#ifndef pte_batch_hint >>> +/** >>> + * pte_batch_hint - Number of pages that can be added to batch without scanning. >>> + * @ptep: Page table pointer for the entry. >>> + * @pte: Page table entry. >>> + * >>> + * Some architectures know that a set of contiguous ptes all map the same >>> + * contiguous memory with the same permissions. In this case, it can provide a >>> + * hint to aid pte batching without the core code needing to scan every pte. >> >> I think we might want to document here the expectation regarding >> dirty/accessed bits. folio_pte_batch() will ignore dirty bits only with >> FPB_IGNORE_DIRTY. But especially for arm64, it makes sense to ignore them >> always when batching, because the dirty bit may target any pte part of the >> cont-pte group either way. >> >> Maybe something like: >> >> " >> An architecture implementation may only ignore the PTE accessed and dirty bits. >> Further, it may only ignore the dirty bit if that bit is already not >> maintained with precision per PTE inside the hinted batch, and ptep_get() >> would already have to collect it from various PTEs. >> " > > I'm proposing to simplify this to: > > " > An architecture implementation may ignore the PTE accessed state. Further, the > dirty state must apply atomically to all the PTEs described by the hint. > " > > Which I think more accurately describes the requirement. Shout if you disagree. I'm not 100% sure if the "must apply atomically" is clear without all of the cont-pte details and ptep_get(). But I fail to describe it in a better way. It's all better compared to what we had before, so LGTM :) -- Cheers, David / dhildenb