On Tue, Feb 05, 2008 at 02:06:23PM -0800, Christoph Lameter wrote: > On Tue, 5 Feb 2008, Andrea Arcangeli wrote: > > > On Tue, Feb 05, 2008 at 10:17:41AM -0800, Christoph Lameter wrote: > > > The other approach will not have any remote ptes at that point. Why would > > > there be a coherency issue? > > > > It never happens that two threads writes to two different physical > > pages by working on the same process virtual address. This is an issue > > only for KVM which is probably ok with it but certainly you can't > > consider the dependency on the page-pin less fragile or less complex > > than my PT lock approach. > > You can avoid the page-pin and the pt lock completely by zapping the > mappings at _start and then holding off new references until _end.
Avoid the PT lock? The PT lock has to be taken anyway by the linux VM. "holding off new references until _end" = per-range mutex less scalar and more expensive than the PT lock that has to be taken anyway. > As I said the implementation is up to the caller. Not sure what > XPmem is using there but then XPmem is not using follow_page. The GRU > would be using a lightway way of locking not rbtrees. "lightway way of locking" = mm-wide-mutex (not necessary at all if we take advantage of the per-pte-scalar PT lock that has to be taken anyway like in my patch) > Maybe that is true for KVM but certainly not true for the GRU. The GRU is > designed to manage several petabytes of memory that may be mapped by a > series of Linux instances. If a process only maps a small chunk of 4 > Gigabytes then we already have to deal with 1 mio callbacks. KVM is also going to map a lot of stuff, but mapping involves mmap, munmap/mremap/mprotect not. The size of mmap is irrelevant in both approaches. optimizing do_exit by making the tlb-miss runtime slower doesn't sound great to me and that's your patch does if you force GRU to use it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
