Re: [PATCH] mm/huge_memory: allow huge pfnmaps regardless of THP mode

[Saravanan D]

On Fri, Aug 21, 2026 at 09:03:15AM +0100, Lorenzo Stoakes (ARM) wrote:
> In any case if you'd taken 5 minutes to search the mailing list you'd see
> this was:
>
> a. Already submitted (so your patch reads like plagiarism).
> b. Already rejected in favour of me doing an actually sensible solution.
>
> https://lore.kernel.org/linux-mm/anL-NZkNMSSxN0YN@lucifer/

Apologies and please disregard my patch. I had not
searched the list before sending and was unaware of Cédric's patch
and your rework. Mine came from an independent observation of slow
VM boot times on Ubuntu based hosts running cloud-hypervisor with H100
GPUs. The patch was prepared with AI assistance and should have
carried an Assisted-by tag. All of my future submissions will.

I backported the diff you attached in your earlier response to
a 6.17 based kernel and ran it on a HGX host with four H100 GPUs,
each exposing a 128 GiB BAR1, with cloud-hypervisor. THP
mode was the Ubuntu default - madvise in all runs.

                       VFIO_IOMMU_MAP_DMA       4 GPU VM boot
                       per 128 GiB BAR
  6.17 unpatched             20.7s                   97s
  6.17 + your diff            0.4s                   17s

Each BAR mapped with 128 PUD faults. Your approach will definitely
improve VM boot times in our production. Very grateful for your
contribution.

Thanks,
Saravanan D.