[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] sparse M2P table
I'm in the process of putting together patches to eliminate undue overhead resulting from Xen's current assumption on a non-sparse machine address map. After removing large holes (symmetric across all nodes) from the machine address map and after also mapping the resulting (much smaller) frame table sparsely (to account for smaller holes distinct for one or more nodes), I intended to also map the P2M table sparsely. However, there's a tools side assumption (for domain save) on this table being contiguously populated. While this could be relatively easily fixed in tools, I'm wondering if there are other dependencies on this table (or its read-only equivalent readable by all guests) to be non-sparse. In particular, while I can easily see that Linux has always been careful to access the read-only copy of the table with exception fixup, I don't know whether that would also apply to the other PV OSes (Solaris, NetBSD, ???). One alternative would be to dedicate a zero-filled 2M page for all these holes, but I have to admit that this doesn't seem very attractive. Another option would be to use a made-up MFN to represent the holes, allowing Xen (once they get fed back into mmu_update) to recognize this and simply ignore the mapping request (after all the tools should not access these ranges anyway). This wouldn't address potential issues of non-Linux guests with a sparse R/O M2P table though. Other thoughts? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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