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[2003:d8:2f2d:2400:4052:3b5:fff9:4ed0]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b087a9sm17020666f8f.55.2025.06.18.04.52.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Jun 2025 04:52:38 -0700 (PDT) Message-ID: Date: Wed, 18 Jun 2025 13:52:37 +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: Jason Gunthorpe Cc: lizhe.67@bytedance.com, 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: <20250617152210.GA1552699@ziepe.ca> <20250618062820.8477-1-lizhe.67@bytedance.com> <20250618113626.GK1376515@ziepe.ca> <9c31da33-8579-414a-9b2a-21d7d8049050@redhat.com> <20250618114629.GL1376515@ziepe.ca> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18.06.25 13:46, Jason Gunthorpe wrote: > On Wed, Jun 18, 2025 at 01:42:09PM +0200, David Hildenbrand wrote: >> On 18.06.25 13:40, David Hildenbrand wrote: >>> On 18.06.25 13:36, Jason Gunthorpe wrote: >>>> On Wed, Jun 18, 2025 at 02:28:20PM +0800, lizhe.67@bytedance.com wrote: >>>>> On Tue, 17 Jun 2025 12:22:10 -0300, jgg@ziepe.ca wrote: >>>>>> + 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)); >>>>>> + >>>>>> + unpin_user_folio_dirty_locked(folio, nr_pages, >>>>>> + dma->prot & IOMMU_WRITE); >>>>> >>>>> Are you suggesting that we should directly call >>>>> unpin_user_page_range_dirty_lock() here (patch 3/3) instead? >>>> >>>> I'm saying you should not have the word 'folio' inside the VFIO. You >>>> accumulate a contiguous range of pfns, by only checking the pfn, and >>>> then call >>>> >>>> unpin_user_page_range_dirty_lock(pfn_to_page(first_pfn)...); >>>> >>>> No need for any of this. vfio should never look at the struct page >>>> except as the last moment to pass the range. >>> >>> Hah, agreed, that's actually simpler and there is no need to factor >>> anything out. >> >> Ah, no, wait, the problem is that we don't know how many pages we can >> supply, because there might be is_invalid_reserved_pfn() in the range ... > > You stop batching when you hit any invalid_reserved_pfn and flush it. > > It still has to check read back and check every PFN to make sure it is > contiguous, checking reserved too is not a problemm. I thought we also wanted to optimize out the is_invalid_reserved_pfn() check for each subpage of a folio. pfn_valid() + pfn_to_page() are not super cheap in some relevant configs IIRC. -- Cheers, David / dhildenb