[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH] Add hypercall to mark superpages to improve performance
On 02/05/2010 14:34, "Dave McCracken" <dcm@xxxxxxxx> wrote: > One outstanding issue I see is how to handle readonly mappings. If we follow > the model of regular page typecount, readonly mappings of superpages would not > conflict with the "conflicts with superpage" type. This means a subsequent > attempt to change it to a read/write mapping could fail, just like with a > regular page. Or we could count all mappings of superpages as if they were > read/write. I'd keep an extra refcount in superpage_info to track read-only mappings (or all superpage mappings, as page->count_info does for 4kB mappings). It's trivial extra space and avoids having unexpected extra restrictions on read-only superpage mappings. > What are your thoughts? It seems fairly simple and elegant to me, and at this > point I don't see any big holes in it. It does mean that creating/destroying pagetable pages causes an extra locked read-modify-write cycle on a non-local cacheline (superpage_info refcount). Would this be significant? Not sure. I guess we'd only be doing it for guests with the superpage capability configured, and we could do some performance comparisons with the capability enabled/disabled. I think overall I quite like your suggestion. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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