linux-kernel - [PATCH v2 0/5] vfio/type1: optimize vfio_pin_pages_remote() and vfio_unpin_pages

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Message-ID: <20250704062602.33500-1-lizhe.67@bytedance.com>
Date: Fri,  4 Jul 2025 14:25:57 +0800
From: lizhe.67@...edance.com
To: alex.williamson@...hat.com,
	akpm@...ux-foundation.org,
	david@...hat.com,
	peterx@...hat.com,
	jgg@...pe.ca
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lizhe.67@...edance.com
Subject: [PATCH v2 0/5] vfio/type1: optimize vfio_pin_pages_remote() and vfio_unpin_pages_remote()

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              |  20 ++++++
 2 files changed, 110 insertions(+), 21 deletions(-)

---
Changelogs:

v1->v2:
- Update the performance test results.
- The function num_pages_contiguous() is extracted and placed in a
  separate commit.
- The phrase 'for large folio' has been removed from the patchset title.

v1: https://lore.kernel.org/all/20250630072518.31846-1-lizhe.67@bytedance.com/

-- 
2.20.1