[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Seamlessly sharing identical memory pages among domains
> > > > Doing a proper shared cache is slightly trickier given the > > paravirtualised memory interface -- we'd have to introduce guests > > to a new kind of write fault: "A write fault has occurred, and > > you'll have to copy the page because this machine page is > > immutable as it is already shared with other domains". Modifying > > Linux to handle this wouldn't be hard. > > Would this just involve adding an extra error code to what x86 already > uses and then modifying the guest to understand that that error code > means that the page has to be COWed? Yep. The only slight subtlety is that that the page in question may appear in multiple page tables and at multiple VAs: if the page is truly read-write shared in the guest (e.g. sysv shared memory [*]) then it it will be necessary to find all the ptes and patch them to the newly allocated machine frame. I think such pages are rare, and tracking them down by scanning the list of vma's that are mapping the object (e.g. a file) in question is pretty easy and quick. However, this would most sensibly be done by making minor modifications to architecture independent code, which is something we try to avoid. I guess we could just have arch xen grub its way through the higher-level data structures... Ian [*] Hmm, do memory mapped files behave like this too? I can't remember. ------------------------------------------------------- This SF.Net email is sponsored by: Oracle 10g Get certified on the hottest thing ever to hit the market... Oracle 10g. Take an Oracle 10g class now, and we'll give you the exam FREE. http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/xen-devel
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