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

[Alistair Popple]

John Hubbard <jhubbard@xxxxxxxxxx> writes:

> On 10/29/24 9:42 PM, Christoph Hellwig wrote:
>> On Tue, Oct 29, 2024 at 09:39:15PM -0700, John Hubbard wrote:
>>> I expect I could piece together something with Nouveau, given enough
>>> time and help from Ben Skeggs and Danillo and all...
>>>
>>> Yes, this originated with the out of tree driver. But it never occurred
>>> to me that upstream be uninterested in an obvious fix to an obvious
>>> regression.
>> 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.

- Alistair

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

> thanks,