linux-kernel - Re: [PATCH] vfio/type1: optimize vfio_pin_pages

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Message-ID: <20250516141816.GB530183@ziepe.ca>
Date: Fri, 16 May 2025 11:18:16 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: lizhe.67@...edance.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, muchun.song@...ux.dev,
	Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH] vfio/type1: optimize vfio_pin_pages_remote() for
 hugetlbfs folio

On Thu, May 15, 2025 at 03:19:46PM -0600, Alex Williamson wrote:
> On Tue, 13 May 2025 11:57:30 +0800
> lizhe.67@...edance.com wrote:
> 
> > From: Li Zhe <lizhe.67@...edance.com>
> > 
> > When vfio_pin_pages_remote() is called with a range of addresses that
> > includes hugetlbfs 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.
> > 
> > This patch optimize this process by batching the statistics counting
> > operations.
> > 
> > The performance test results for completing the 8G VFIO IOMMU DMA mapping,
> > obtained through trace-cmd, are as follows. In this case, the 8G virtual
> > address space has been mapped to physical memory using hugetlbfs with
> > pagesize=2M.
> > 
> > Before this patch:
> > funcgraph_entry:      # 33813.703 us |  vfio_pin_map_dma();
> > 
> > After this patch:
> > funcgraph_entry:      # 15635.055 us |  vfio_pin_map_dma();
> > 
> > Signed-off-by: Li Zhe <lizhe.67@...edance.com>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 49 +++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> 
> Hi,
> 
> Thanks for looking at improvements in this area...

Why not just use iommufd? Doesn't it already does all these
optimizations?

Indeed today you can use iommufd with a memfd handle which should
return the huge folios directly from the hugetlbfs and we never
iterate with 4K pages.

Jason