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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. It would be very rare for reserved PFNs and non reserved will to be mixed within the same range. So this patch utilizes the has_rsvd variable introduced in the previous patch to determine whether batch put_pfn() operations can be performed. Moreover, compared to put_pfn(), unpin_user_page_range_dirty_lock() is capable of handling large folio scenarios more efficiently. The performance test results for completing the 16G VFIO IOMMU DMA unmapping are as follows. Base(v6.16): ------- AVERAGE (MADV_HUGEPAGE) -------- VFIO UNMAP DMA in 0.141 s (113.7 GB/s) ------- AVERAGE (MAP_POPULATE) -------- VFIO UNMAP DMA in 0.307 s (52.2 GB/s) ------- AVERAGE (HUGETLBFS) -------- VFIO UNMAP DMA in 0.135 s (118.6 GB/s) With this patchset: ------- AVERAGE (MADV_HUGEPAGE) -------- VFIO UNMAP DMA in 0.044 s (363.2 GB/s) ------- AVERAGE (MAP_POPULATE) -------- VFIO UNMAP DMA in 0.289 s (55.3 GB/s) ------- AVERAGE (HUGETLBFS) -------- VFIO UNMAP DMA in 0.044 s (361.3 GB/s) For large folio, we achieve an over 67% performance improvement in the VFIO UNMAP DMA item. For small folios, the performance test results appear to show a slight improvement. Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Li Zhe <lizhe.67@bytedance.com> Reviewed-by: David Hildenbrand <david@redhat.com> Acked-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/20250814064714.56485-6-lizhe.67@bytedance.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.