> Right, but then you need to set that in the VMA's, and thus gone is your > nice fast g_u_p() that doesn't touch VMAs :-)
Registering memory is a slow path thing in the RDMA world. Speeding it up is nice, so we make userspace do the madvise(VM_DONTCOPY) if it cares but if it doesn't it can leave it out. > > Yes, but unfortunately MPI says apps can allocate memory however they > > damn well please... in any case these issues are all-too-well-known in > > the RDMA world for quite a while. > Yup. What do you think of the idea of pre-COWing pages with an elevated > count at fork time ? Super-duper sucks if the first thing the child does is exec() :) Also if the parent has registered > half the memory in the system then it's instant OOM. So not that useful for the RDMA case :) The one thing that might make sense is to pre-COW any partial pages that the parent has registered -- ie if half a page can be used by the child, at least pre-COW that, but leave all the full pages with VM_DONTCOPY. - R. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev