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
