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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id fm13-20020a05600c0c0d00b0040b37f107c4sm2664041wmb.16.2023.12.21.01.29.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Dec 2023 01:29:10 -0800 (PST) Message-ID: <71f2ceb0-ee76-4832-ace5-24403ba54283@redhat.com> Date: Thu, 21 Dec 2023 10:29:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 04/40] mm/rmap: introduce and use hugetlb_try_dup_anon_rmap() To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Hugh Dickins , Ryan Roberts , Yin Fengwei , Mike Kravetz , Muchun Song , Peter Xu References: <20231220224504.646757-1-david@redhat.com> <20231220224504.646757-5-david@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-Rspamd-Queue-Id: A39C718000B X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: weua18irpe67tc8qhr9jaipy8rfteuob X-HE-Tag: 1703150956-138891 X-HE-Meta: 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 QzUN3I8a 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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 21.12.23 05:40, Matthew Wilcox wrote: > On Wed, Dec 20, 2023 at 11:44:28PM +0100, David Hildenbrand wrote: >> hugetlb rmap handling differs quite a lot from "ordinary" rmap code. >> For example, hugetlb currently only supports entire mappings, and treats >> any mapping as mapped using a single "logical PTE". Let's move it out >> of the way so we can overhaul our "ordinary" rmap. >> implementation/interface. >> >> So let's introduce and use hugetlb_try_dup_anon_rmap() to make all >> hugetlb handling use dedicated hugetlb_* rmap functions. >> >> Add sanity checks that we end up with the right folios in the right >> functions. >> >> Note that is_device_private_page() does not apply to hugetlb. >> >> Reviewed-by: Yin Fengwei >> Reviewed-by: Ryan Roberts >> Signed-off-by: David Hildenbrand > > Reviewed-by: Matthew Wilcox (Oracle) > Thanks! >> +static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma, >> + struct folio *folio) > > I particularly like it that you introduced this. And a later patch even removes page_needs_cow_for_dma() :) A note that we have one remaining user of page_maybe_dma_pinned(). Instead of converting that code to folios, we should probably just remove that pte_is_pinned() handling completely: it's inconsistent (only checks PTEs) and cannot handle concurrent GUP-fast. It's a leftover from the COW issues we had before PageAnonExclusive. [I've had patch lying around to do that for a long time, but never sent it] > >> +static inline int hugetlb_try_dup_anon_rmap(struct folio *folio, >> + struct vm_area_struct *vma) >> +{ >> + VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio); >> + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); >> + >> + if (PageAnonExclusive(&folio->page)) { > > I wonder if we need a folio_test_hugetlb_anon_exclusive() to make this > a little more ergonomic? > >> + if (unlikely(folio_needs_cow_for_dma(vma, folio))) >> + return -EBUSY; >> + ClearPageAnonExclusive(&folio->page); > > ... and set/clear variants. > I thought about that as well, and even going a step further and instead of having PageAnonExclusive checks outside rmap code, have something like the following instead: hugetlb_test_anon_rmap_exclusive() folio_test_anon_rmap_exclusive_[pte|pmd]() I added that to my TODO list, because it results again in a bigger patchset (especially also in GUP). -- Cheers, David / dhildenb