On 09/13/2011 07:07 PM, Avi Kivity wrote: > On 08/30/2011 05:38 AM, Xiao Guangrong wrote: >> Detecting write-flooding does not work well, when we handle page written, if >> the last speculative spte is not accessed, we treat the page is >> write-flooding, however, we can speculative spte on many path, such as pte >> prefetch, page synced, that means the last speculative spte may be not point >> to the written page and the written page can be accessed via other sptes, so >> depends on the Accessed bit of the last speculative spte is not enough >> >> Instead of detected page accessed, we can detect whether the spte is accessed >> after it is written, if the spte is not accessed but it is written frequently, >> we treat is not a page table or it not used for a long time >> >> > > The spte may not be accessed, but other sptes in the same page can be accessed. An example is the fixmap area for kmap_atomic(), there will be a lot of pte writes but other sptes will be accessed without going through soft-mmu at all. I think this kind of shadow pae is mostly the last page table(level=1), maybe we can skip the write-flooding for the last shadow page, because the last shadow page can become unsync and it can not let page table write-protected. > I think you have to read the parent_ptes->spte.accessed bits to be sure. > I guess the overload of this way is little high: - it needs to walk parent ptes for every shadow pages - we need to clear the parent_ptes->spte.accessed bit when the page is written, and the tlb flush is needed. no? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
