Messages in this thread | | | From | Roland Dreier <> | Subject | Re: FW: [PATCH] powerpc/mm: Export HPAGE_SHIFT | Date | Wed, 04 Feb 2009 21:33:34 -0800 |
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> 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.
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