Re: [PATCH] mm/huge_memory: let special huge VMAs bypass the THP policy check

[Lorenzo Stoakes (ARM)]

On Wed, Aug 05, 2026 at 09:15:24AM -0300, Jason Gunthorpe wrote:
> On Wed, Aug 05, 2026 at 07:55:40AM +0200, Cédric Le Goater wrote:
>
> > The result: each 256 GB BAR is mapped at 4 KiB granularity -- 67 million
> > page faults per GPU instead of a few thousand PMD/PUD faults. On hosts
> > with 8 GPUs (2 TB of BAR space), this causes VM boot times to degrade
> > severely, with 99.98% of CPU time spent in the VFIO BAR mapping path.
>
> Broadly upstream we expect people to use iommufd and dmabuf for these
> configurations to avoid all this nonsense overhead. :\

Point taken on that :) but I think it's generally reasonable in line with the
huge PFN map changes to do something like I suggested.

>
> Jason

--
Cheers, Lorenzo