On Wed, Aug 25, 2021 at 02:27:08PM +0200, Christian König wrote:
Am 25.08.21 um 14:18 schrieb Jason Gunthorpe:
On Wed, Aug 25, 2021 at 08:17:51AM +0200, Christian König wrote:
The only real option where you could do P2P with buffer pinning are those compute boards where we know that everything is always accessible to everybody and we will never need to migrate anything. But even then you want some mechanism like cgroups to take care of limiting this. Otherwise any runaway process can bring down your whole system.
Why? It is not the pin that is the problem, it was allocating GPU dedicated memory in the first place. pinning it just changes the sequence to free it. No different than CPU memory.
Pinning makes the memory un-evictable.
In other words as long as we don't pin anything we can support as many processes as we want until we run out of swap space. Swapping sucks badly because your applications become pretty much unuseable, but you can easily recover from it by killing some process.
With pinning on the other hand somebody sooner or later receives an -ENOMEM or -ENOSPC and there is no guarantee that this goes to the right process.
It is not really different - you have the same failure mode once the system runs out of swap.
This is really the kernel side trying to push a policy to the user side that the user side doesn't want..
Dedicated systems are a significant use case here and should be supported, even if the same solution wouldn't be applicable to someone running a desktop.
Jason