linux-kernel - Re: [PATCH v4 0/5] vfio/type1: optimize vfio_pin_pages_remote() and vfio_unpin_pages

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Message-ID: <20250716142102.1db0ec85.alex.williamson@redhat.com>
Date: Wed, 16 Jul 2025 14:21:02 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: lizhe.67@...edance.com
Cc: akpm@...ux-foundation.org, david@...hat.com, jgg@...pe.ca,
 peterx@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH v4 0/5] vfio/type1: optimize vfio_pin_pages_remote() and
 vfio_unpin_pages_remote()

On Thu, 10 Jul 2025 16:53:50 +0800
lizhe.67@...edance.com wrote:

> From: Li Zhe <lizhe.67@...edance.com>
> 
> This patchset is an integration of the two previous patchsets[1][2].
> 
> When vfio_pin_pages_remote() is called with a range of addresses that
> includes large folios, the function currently performs individual
> statistics counting operations for each page. This can lead to significant
> performance overheads, especially when dealing with large ranges of pages.
> 
> The function vfio_unpin_pages_remote() has a similar issue, where executing
> put_pfn() for each pfn brings considerable consumption.
> 
> This patchset primarily optimizes the performance of the relevant functions
> by batching the less efficient operations mentioned before.
> 
> The first two patch optimizes the performance of the function
> vfio_pin_pages_remote(), while the remaining patches optimize the
> performance of the function vfio_unpin_pages_remote().
> 
> The performance test results, based on v6.16-rc4, for completing the 16G
> VFIO MAP/UNMAP DMA, obtained through unit test[3] with slight
> modifications[4], are as follows.
> 
> Base(6.16-rc4):
> ./vfio-pci-mem-dma-map 0000:03:00.0 16
> ------- AVERAGE (MADV_HUGEPAGE) --------
> VFIO MAP DMA in 0.047 s (340.2 GB/s)
> VFIO UNMAP DMA in 0.135 s (118.6 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 (310.5 GB/s)
> VFIO UNMAP DMA in 0.136 s (117.3 GB/s)
> 
> With this patchset:
> ------- AVERAGE (MADV_HUGEPAGE) --------
> VFIO MAP DMA in 0.027 s (600.7 GB/s)
> VFIO UNMAP DMA in 0.045 s (357.0 GB/s)
> ------- AVERAGE (MAP_POPULATE) --------
> VFIO MAP DMA in 0.261 s (61.4 GB/s)
> VFIO UNMAP DMA in 0.288 s (55.6 GB/s)
> ------- AVERAGE (HUGETLBFS) --------
> VFIO MAP DMA in 0.031 s (516.4 GB/s)
> VFIO UNMAP DMA in 0.045 s (353.9 GB/s)
> 
> For large folio, we achieve an over 40% performance improvement for VFIO
> MAP DMA and an over 66% performance improvement for VFIO DMA UNMAP. For
> small folios, the performance test results show a slight improvement with
> the performance before optimization.
> 
> [1]: https://lore.kernel.org/all/20250529064947.38433-1-lizhe.67@bytedance.com/
> [2]: https://lore.kernel.org/all/20250620032344.13382-1-lizhe.67@bytedance.com/#t
> [3]: https://github.com/awilliam/tests/blob/vfio-pci-mem-dma-map/vfio-pci-mem-dma-map.c
> [4]: https://lore.kernel.org/all/20250610031013.98556-1-lizhe.67@bytedance.com/
> 
> Li Zhe (5):
>   mm: introduce num_pages_contiguous()
>   vfio/type1: optimize vfio_pin_pages_remote()
>   vfio/type1: batch vfio_find_vpfn() in function
>     vfio_unpin_pages_remote()
>   vfio/type1: introduce a new member has_rsvd for struct vfio_dma
>   vfio/type1: optimize vfio_unpin_pages_remote()
> 
>  drivers/vfio/vfio_iommu_type1.c | 111 ++++++++++++++++++++++++++------
>  include/linux/mm.h              |  23 +++++++
>  2 files changed, 113 insertions(+), 21 deletions(-)

Applied to vfio next branch for v6.17.  Thanks,

Alex