Zhao Forrest wrote: >>> Normally swapping mechanism choose the Least Recently Used(LRU) pages >>> of a process to be swapped out. When KVM uses MMU notifier in linux >>> kernel to implement swapping for VM, could KVM choose LRU pages of a >>> VM to swap out? If so, could you give a brief description about how >>> this is implemented? >>> >>> >> The Linux memory manager approximates LRU by scanning pages for the >> accessed bit, which is set in the pte by the processor when a page is >> accessed through that pte. mmu notifiers provide a callback for the >> check, so that kvm can check the accessed bit on the shadow ptes. >> > > Linux kernel maintains a reverse mapping from a page frame to all page tables > pointing to this page frame. Does KVM need to maintain a similar reverse > mapping > from a page frame to all shadow page tables pointing to this page frame? >
Yes, look for 'rmap' in mmu.c. The purpose was initially to be able to write-protect shadowed guest page tables without horrible worst-case performance, and was later extended to swapping. With mmu notifiers, when the kernel swaps a page, it first scans its own rmap, then calls kvm which scans the kvm rmap. So one way to look at mmu notifiers is as rmap extenders (that's not the whole story -- kvm ptes are in a different format than Linux ptes, so the code has to be different). -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- 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
