[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: [PATCH] Add hypercall to mark superpages to improve performance
On 03/05/2010 17:09, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote: >> It should be simple enough to also check superpage->count_info in those >> places. So the total mappings of a page would be page->count_info + >> superpage->count_info. Good thing you suggested we also have a count in the >> superpage_info struct :) > > I think you're going to have trouble handling two separate reference counts, > for superpages and single pages, in a race-free manner that is any better > than checking/updating reference counts across all pages in a superpage on > first superpage mapping. For example: When making first superpage mapping, how do you know that all pages belong to the relevant domain, without scanning every page_info? When destructing last superpage mapping (or single-page mapping) how do you safely check the 'other' reference count to decide whether the page is freeable, without having races (last single-page and superpage mappings could be destructed concurrently, need to ensure any given page gets freed exactly once). And I could think of others no doubt... Just pointing out how careful you have to be if you think you can avoid the naïve refcount-updatign algorithms I suggested. I'd rather shoot down the obvious races before you do the coding. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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