On Thu, Feb 23, 2023 at 09:18:23AM -0800, T.J. Mercier wrote: > > Solving that problem means figuring out when every cgroup stops using > > the memory - pinning or not. That seems to be very costly. > > > This is the current behavior of accounting for memfds, and I suspect > any kind of shared memory. > > If cgroup A creates a memfd, maps and faults in pages, shares the > memfd with cgroup B and then A unmaps and closes the memfd, then > cgroup A is still charged for the pages it faulted in. As we discussed, as long as the memory is swappable then eventually memory pressure on cgroup A will evict the memfd pages and then cgroup B will swap it in and be charged for it. > FWIW this is also the behavior I was trying to use to attribute > dma-buffers to their original allocators. Whoever touches it first > gets charged as long as the memory is alive somewhere. > > Can't we do the same thing for pins? If pins are tracked independently from memcg then definately not, a process in cgroup A should never be able to make a charge on cgroup B as a matter of security. If pins are part of the memcg then we can't always turn the pin request in to a NOP - the current cgroup always has to be charged for the memory. Otherwise what is the point from a security perspective? Jason
