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

[John Hubbard <jhubbard@nvidia.com>]

On 10/29/24 11:18 PM, Alistair Popple wrote:
> John Hubbard <jhubbard@nvidia.com> writes:
>> On 10/29/24 9:42 PM, Christoph Hellwig wrote:
>>> On Tue, Oct 29, 2024 at 09:39:15PM -0700, John Hubbard wrote:
...
>>> Because pinning down these amounts of memoryt is completely insane.
>>> I don't mind the switch to kvmalloc, but we need to put in an upper
>>> bound of what can be pinned.
>>
>> I'm wondering though, how it is that we decide how much of the user's
>> system we prevent them from using? :)  People with hardware accelerators
>> do not always have page fault capability, and yet these troublesome
>> users insist on stacking their system full of DRAM and then pointing
>> the accelerator to it.
>>
>> How would we choose a value? Memory sizes keep going up...
> 
> The obvious answer is you let users decide. I did have a patch series to
> do that via a cgroup[1]. However I dropped that series mostly because I
> couldn't find any users of such a limit to provide feedback on how they
> would use it or how they wanted it to work.
> 

Trawling through the discussion there, I see that Jason Gunthorpe mentioned:

"Things like VFIO & KVM use cases effectively pin 90% of all system memory"

...which means that we'll be able to get that in-tree call trace that 
Christoph
is asking for, pretty soon. No GPUs required. :)


thanks,
-- 
John Hubbard

> - Alistair
> 
> [1] - https://lore.kernel.org/linux-mm/cover.c238416f0e82377b449846dbb2459ae9d7030c8e.1675669136.git-series.apopple@nvidia.com/
>