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(p200300cbc7302200722983b1524e283a.dip0.t-ipconnect.de. [2003:cb:c730:2200:7229:83b1:524e:283a]) by smtp.gmail.com with ESMTPSA id t6-20020a05600c450600b0040fc56712e8sm8754772wmo.17.2024.02.12.05.43.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Feb 2024 05:43:37 -0800 (PST) Message-ID: <6d452a1a-1edc-4e97-8b39-99dc48315bb8@redhat.com> Date: Mon, 12 Feb 2024 14:43:35 +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" References: <20240202080756.1453939-1-ryan.roberts@arm.com> <20240202080756.1453939-23-ryan.roberts@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: <20240202080756.1453939-23-ryan.roberts@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: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-mm@kvack.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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 think there are some more details to it, but I'm hoping something along the lines above is sufficient. > + > #ifndef pte_advance_pfn > static inline pte_t pte_advance_pfn(pte_t pte, unsigned long nr) > { > diff --git a/mm/memory.c b/mm/memory.c > index 65fbe4f886c1..902665b27702 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -988,16 +988,21 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > { > unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); > const pte_t *end_ptep = start_ptep + max_nr; > - pte_t expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, 1), flags); > - pte_t *ptep = start_ptep + 1; > + pte_t expected_pte = __pte_batch_clear_ignored(pte, flags); > + pte_t *ptep = start_ptep; > bool writable; > + int nr; > > if (any_writable) > *any_writable = false; > > VM_WARN_ON_FOLIO(!pte_present(pte), folio); > > - while (ptep != end_ptep) { > + nr = pte_batch_hint(ptep, pte); > + expected_pte = pte_advance_pfn(expected_pte, nr); > + ptep += nr; > + *Maybe* it's easier to get when initializing expected_pte+ptep only once. Like: [...] pte_t expected_pte, *ptep; [...] nr = pte_batch_hint(start_ptep, pte); expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags); ptep = start_ptep + nr; > + while (ptep < end_ptep) { > pte = ptep_get(ptep); > if (any_writable) > writable = !!pte_write(pte); > @@ -1011,17 +1016,18 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > * corner cases the next PFN might fall into a different > * folio. > */ > - if (pte_pfn(pte) == folio_end_pfn) > + if (pte_pfn(pte) >= folio_end_pfn) > break; > > if (any_writable) > *any_writable |= writable; > > - expected_pte = pte_advance_pfn(expected_pte, 1); > - ptep++; > + nr = pte_batch_hint(ptep, pte); > + expected_pte = pte_advance_pfn(expected_pte, nr); > + ptep += nr; > } > > - return ptep - start_ptep; > + return min(ptep - start_ptep, max_nr); > } Acked-by: David Hildenbrand -- Cheers, David / dhildenb