On Tue, 2010-04-13 at 11:23 +1000, Benjamin Herrenschmidt wrote: > > + * A comment here about on why we have RCU freed page tables might be > > + * interesting, also explaining why we don't need any sort of grace > > + * period for mm_users == 1, and have some home brewn smp_call_func() > > + * for single frees. > > iirc, we are synchronizing with CPUs walking page tables in their hash > or TLB miss code, which is lockless. The mm_users test is a -little- bit > dubious indeed. It may have to be mm_users < 2 && mm == > current->active_mm, ie, we know for sure nobody else is currently > walking those page tables ... > > Tho even than is fishy nowadays. We -can- walk page tables on behave of > another process. In fact, we do it in the Cell SPU code for faulting > page table entries as a result of SPEs taking faults for example. So I'm > starting to suspect that this mm_users optimisation is bogus. > > We -do- want to optimize out the case where there is no user left > though, ie, the MM is dead. IE. The typical exit case. Can't you fix that by having the SPE code take a reference on these mm_structs they're playing with? Poking at one without a ref seems fishy anyway. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
