[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Balloons, crash-dumps, populate-on-demand, and shared zero pages
Paul recently pointed out that a side-effect of having the balloon driver replace guest p2m memory with empty space is that when Windows does a crash dump (perhaps Linux too), when it reaches the pages in the balloon, it will cause a page fault, which can cause cascading crashes and prevent any useful information from reaching the dump file. After thinking about it for a bit, I wondered if it might be better to replace the "populate-on-demand" concept with a "shared-zero-populate-on-demand". Reads to a PoD page would always map to a read-only shared zero page (or superpage, as the case may be). We can change the balloon driver behavior to fill the p2m entries for the balloon with zPoD entries instead of empy p2m entries. As a side-effect, the balloon driver no longer would need to explicitly fill in the p2m entries with ram when deflating the balloon; the tools already tell Xen about memory target increases, so it can increase the PoD "cache"; the balloon driver would simply need to free memory back to the kernel and it the balloon will be populated on-demand by the guest. Any thoughts? -George _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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