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

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Fri, Aug 21, 2026 at 12:32:20PM -0700, Saravanan D wrote:
> 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, always appreciate real world data :)

I will send the actual patch at some point it's on my never ending TODO
list... :)

>
> Thanks,
> Saravanan D.

--
Cheers, Lorenzo