Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a time

[Christoph Hellwig]

On Tue, Oct 29, 2024 at 09:30:41PM -0700, John Hubbard wrote:
> I do, yes. And what happens is that when you use GPUs, drivers like
> to pin system memory, and then point the GPU page tables to that
> memory. For older GPUs that don't support replayable page faults,
> that's required.
> 
> So this behavior has been around forever.
> 
> The customer was qualifying their software and noticed that before
> Linux 6.10, they could allocate >2GB, and with 6.11, they could
> not.
> 
> Whether it is "wise" for user space to allocate that much at once
> is a reasonable question, but at least one place is (or was!) doing
> it.

Still missing a callchain, which make me suspect that it is your weird
out of tree driver, in which case this simply does not matter.