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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532e2324c6sm167302745e9.12.2025.06.17.02.27.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 02:27:51 -0700 (PDT) Message-ID: Date: Tue, 17 Jun 2025 11:27:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty_locked() To: lizhe.67@bytedance.com Cc: akpm@linux-foundation.org, alex.williamson@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterx@redhat.com References: <34560ae6-c598-4474-a094-a657c973156b@redhat.com> <20250617092117.10772-1-lizhe.67@bytedance.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: <20250617092117.10772-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.06.25 11:21, lizhe.67@bytedance.com wrote: > On Tue, 17 Jun 2025 09:43:56 +0200, david@redhat.com wrote: > >> On 17.06.25 06:18, lizhe.67@bytedance.com wrote: >>> From: Li Zhe >>> >>> When vfio_unpin_pages_remote() is called with a range of addresses that >>> includes large folios, the function currently performs individual >>> put_pfn() operations for each page. This can lead to significant >>> performance overheads, especially when dealing with large ranges of pages. >>> >>> This patch optimize this process by batching the put_pfn() operations. >>> >>> The performance test results, based on v6.15, for completing the 16G VFIO >>> IOMMU DMA unmapping, obtained through unit test[1] with slight >>> modifications[2], are as follows. >>> >>> Base(v6.15): >>> ./vfio-pci-mem-dma-map 0000:03:00.0 16 >>> ------- AVERAGE (MADV_HUGEPAGE) -------- >>> VFIO MAP DMA in 0.047 s (338.6 GB/s) >>> VFIO UNMAP DMA in 0.138 s (116.2 GB/s) >>> ------- AVERAGE (MAP_POPULATE) -------- >>> VFIO MAP DMA in 0.280 s (57.2 GB/s) >>> VFIO UNMAP DMA in 0.312 s (51.3 GB/s) >>> ------- AVERAGE (HUGETLBFS) -------- >>> VFIO MAP DMA in 0.052 s (308.3 GB/s) >>> VFIO UNMAP DMA in 0.139 s (115.1 GB/s) >>> >>> Map[3] + This patchset: >>> ------- AVERAGE (MADV_HUGEPAGE) -------- >>> VFIO MAP DMA in 0.028 s (563.9 GB/s) >>> VFIO UNMAP DMA in 0.049 s (325.1 GB/s) >>> ------- AVERAGE (MAP_POPULATE) -------- >>> VFIO MAP DMA in 0.294 s (54.4 GB/s) >>> VFIO UNMAP DMA in 0.296 s (54.1 GB/s) >>> ------- AVERAGE (HUGETLBFS) -------- >>> VFIO MAP DMA in 0.033 s (485.1 GB/s) >>> VFIO UNMAP DMA in 0.049 s (324.4 GB/s) >>> >>> For large folio, we achieve an approximate 64% performance improvement >>> in the VFIO UNMAP DMA item. For small folios, the performance test >>> results appear to show no significant changes. >>> >>> [1]: https://github.com/awilliam/tests/blob/vfio-pci-mem-dma-map/vfio-pci-mem-dma-map.c >>> [2]: https://lore.kernel.org/all/20250610031013.98556-1-lizhe.67@bytedance.com/ >>> [3]: https://lore.kernel.org/all/20250529064947.38433-1-lizhe.67@bytedance.com/ >>> >>> Signed-off-by: Li Zhe >>> --- >>> drivers/vfio/vfio_iommu_type1.c | 35 +++++++++++++++++++++++++++++---- >>> 1 file changed, 31 insertions(+), 4 deletions(-) >>> >>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c >>> index e952bf8bdfab..159ba80082a8 100644 >>> --- a/drivers/vfio/vfio_iommu_type1.c >>> +++ b/drivers/vfio/vfio_iommu_type1.c >>> @@ -806,11 +806,38 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova, >>> bool do_accounting) >>> { >>> long unlocked = 0, locked = vpfn_pages(dma, iova, npage); >>> - long i; >>> >>> - for (i = 0; i < npage; i++) >>> - if (put_pfn(pfn++, dma->prot)) >>> - unlocked++; >>> + while (npage) { >>> + long nr_pages = 1; >>> + >>> + if (!is_invalid_reserved_pfn(pfn)) { >>> + struct page *page = pfn_to_page(pfn); >>> + struct folio *folio = page_folio(page); >>> + long folio_pages_num = folio_nr_pages(folio); >>> + >>> + /* >>> + * For a folio, it represents a physically >>> + * contiguous set of bytes, and all of its pages >>> + * share the same invalid/reserved state. >>> + * >>> + * Here, our PFNs are contiguous. Therefore, if we >>> + * detect that the current PFN belongs to a large >>> + * folio, we can batch the operations for the next >>> + * nr_pages PFNs. >>> + */ >>> + if (folio_pages_num > 1) >>> + nr_pages = min_t(long, npage, >>> + folio_pages_num - >>> + folio_page_idx(folio, page)); >>> + >> >> (I know I can be a pain :) ) > > No, not at all! I really appreciate you taking the time to review my > patch. > >> But the long comment indicates that this is confusing. >> >> >> That is essentially the logic in gup_folio_range_next(). >> >> What about factoring that out into a helper like >> >> /* >> * TODO, returned number includes the provided current page. >> */ >> unsigned long folio_remaining_pages(struct folio *folio, >> struct pages *pages, unsigned long max_pages) >> { >> if (!folio_test_large(folio)) >> return 1; >> return min_t(unsigned long, max_pages, >> folio_nr_pages(folio) - folio_page_idx(folio, page)); >> } >> >> >> Then here you would do >> >> if (!is_invalid_reserved_pfn(pfn)) { >> struct page *page = pfn_to_page(pfn); >> struct folio *folio = page_folio(page); >> >> /* We can batch-process pages belonging to the same folio. */ >> nr_pages = folio_remaining_pages(folio, page, npage); >> >> unpin_user_folio_dirty_locked(folio, nr_pages, >> dma->prot & IOMMU_WRITE); >> unlocked += nr_pages; >> } > > Yes, this indeed makes the code much more comprehensible. Do you think > the implementation of the patch as follows look viable to you? I have > added some brief comments on top of your work to explain why we can > batch-process pages belonging to the same folio. This was suggested by > Alex[1]. > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index e952bf8bdfab..d7653f4c10d5 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -801,16 +801,43 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr, > return pinned; > } > > +/* Returned number includes the provided current page. */ > +static inline unsigned long folio_remaining_pages(struct folio *folio, > + struct page *page, unsigned long max_pages) > +{ > + if (!folio_test_large(folio)) > + return 1; > + return min_t(unsigned long, max_pages, > + folio_nr_pages(folio) - folio_page_idx(folio, page)); > +} Note that I think that should go somewhere into mm.h, and also get used by GUP. So factoring it out from GUP and then using it here. -- Cheers, David / dhildenb