On Fri, 1 Feb 2008, Andrea Arcangeli wrote: > Note that my #v5 doesn't require to increase the page count all the > time, so GRU will work fine with #v5.
But that comes with the cost of firing invalidate_page for every page being evicted. In order to make your single invalidate_range work without it you need to hold a refcount on the page. > invalidate_page[s] is always called before the page is freed. This > will require modifications to the tlb flushing code logic to take > advantage of _pages in certain places. For now it's just safe. Yes so your invalidate_range is still some sort of dysfunctional optimization? Gazillions of invalidate_page's will have to be executed when tearing down large memory areas. > > How does KVM insure the consistency of the shadow page tables? Atomic ops? > > A per-VM mmu_lock spinlock is taken to serialize the access, plus > atomic ops for the cpu. And that would not be enough to hold of new references? With small tweaks this should work with a common scheme. We could also redefine the role of _start and _end slightly to just require that the refs are removed when _end completes. That would allow the KVM page count ref to work as is now and would avoid the individual invalidate_page() callouts. > > The GRU has no page table on its own. It populates TLB entries on demand > > using the linux page table. There is no way it can figure out when to > > drop page counts again. The invalidate calls are turned directly into tlb > > flushes. > > Yes, this is why it can't serialize follow_page with only the PT lock > with your patch. KVM may do it once you add start,end to range_end > only thanks to the additional pin on the page. Right but that pin requires taking a refcount which we cannot do. Frankly this looks as if this is a solution that would work only for KVM. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
