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[2003:d8:2f1a:f500:4346:f17c:2bde:808c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b4708d0959sm13336298f8f.27.2025.07.08.09.05.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 09:05:24 -0700 (PDT) Message-ID: <9a9cea9e-82e7-4411-8927-8ac911b2eb06@redhat.com> Date: Tue, 8 Jul 2025 18:05:23 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 10/11] fuse: optimize direct io large folios processing To: Joanne Koong Cc: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, jlayton@kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, bernd.schubert@fastmail.fm, willy@infradead.org, kernel-team@meta.com References: <20250426000828.3216220-1-joannelkoong@gmail.com> <20250426000828.3216220-11-joannelkoong@gmail.com> <6d9c08dd-c1d0-48bd-aacb-b4300f87d525@redhat.com> From: David Hildenbrand Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.07.25 01:27, Joanne Koong wrote: > On Fri, Jul 4, 2025 at 3:24 AM David Hildenbrand wrote: >> >> On 26.04.25 02:08, Joanne Koong wrote: >>> Optimize processing folios larger than one page size for the direct io >>> case. If contiguous pages are part of the same folio, collate the >>> processing instead of processing each page in the folio separately. >>> >>> Signed-off-by: Joanne Koong >>> Reviewed-by: Jeff Layton >>> --- >>> fs/fuse/file.c | 55 +++++++++++++++++++++++++++++++++++++------------- >>> 1 file changed, 41 insertions(+), 14 deletions(-) >>> >>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c >>> index 9a31f2a516b9..61eaec1c993b 100644 >>> --- a/fs/fuse/file.c >>> +++ b/fs/fuse/file.c >>> @@ -1490,7 +1490,8 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii, >>> } >>> >>> while (nbytes < *nbytesp && nr_pages < max_pages) { >>> - unsigned nfolios, i; >>> + struct folio *prev_folio = NULL; >>> + unsigned npages, i; >>> size_t start; >>> >>> ret = iov_iter_extract_pages(ii, &pages, >>> @@ -1502,23 +1503,49 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii, >>> >>> nbytes += ret; >>> >>> - nfolios = DIV_ROUND_UP(ret + start, PAGE_SIZE); >>> + npages = DIV_ROUND_UP(ret + start, PAGE_SIZE); >>> >>> - for (i = 0; i < nfolios; i++) { >>> - struct folio *folio = page_folio(pages[i]); >>> - unsigned int offset = start + >>> - (folio_page_idx(folio, pages[i]) << PAGE_SHIFT); >>> - unsigned int len = min_t(unsigned int, ret, PAGE_SIZE - start); >>> + /* >>> + * We must check each extracted page. We can't assume every page >>> + * in a large folio is used. For example, userspace may mmap() a >>> + * file PROT_WRITE, MAP_PRIVATE, and then store to the middle of >>> + * a large folio, in which case the extracted pages could be >>> + * >>> + * folio A page 0 >>> + * folio A page 1 >>> + * folio B page 0 >>> + * folio A page 3 >>> + * >>> + * where folio A belongs to the file and folio B is an anonymous >>> + * COW page. >>> + */ >>> + for (i = 0; i < npages && ret; i++) { >>> + struct folio *folio; >>> + unsigned int offset; >>> + unsigned int len; >>> + >>> + WARN_ON(!pages[i]); >>> + folio = page_folio(pages[i]); >>> + >>> + len = min_t(unsigned int, ret, PAGE_SIZE - start); >>> + >>> + if (folio == prev_folio && pages[i] != pages[i - 1]) { >> >> I don't really understand the "pages[i] != pages[i - 1]" part. >> >> Why would you have to equal page pointers in there? >> > > The pages extracted are user pages from a userspace iovec. AFAICT, > there's the possibility, eg if userspace mmaps() the file with > copy-on-write, that the same physical page could back multiple > contiguous virtual addresses. Yes, I but I was rather curious why that would be a condition we are checking. It's quite the ... corner case :) > >> >> Something that might be simpler to understand and implement would be using >> >> num_pages_contiguous() >> >> from >> >> https://lore.kernel.org/all/20250704062602.33500-2-lizhe.67@bytedance.com/T/#u >> >> and then just making sure that we don't exceed the current folio, if we >> ever get contiguous pages that cross a folio. > > Thanks for the link. I think here it's common that the pages array > would hold pages from multiple different folios, so maybe a new helper > num_pages_contiguous_folio() would be useful to return back the number > of contiguous pages that are within the scope of the same folio. Yes, something like that can be useful. -- Cheers, David / dhildenb