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    SubjectRe: [PATCH v2 3/3] KVM: remove dummy pages
    On 07/26/2012 04:56 PM, Avi Kivity wrote:
    > On 07/26/2012 06:58 AM, Xiao Guangrong wrote:
    >> Currently, kvm allocates some pages and use them as error indicators,
    >> it wastes memory and is not good for scalability
    >>
    >> Base on Avi's suggestion, we use the error codes instead of these pages
    >> to indicate the error conditions
    >>
    >>
    >> +static pfn_t get_bad_pfn(void)
    >> +{
    >> + return -ENOENT;
    >> +}
    >> +
    >> +pfn_t get_fault_pfn(void)
    >> +{
    >> + return -EFAULT;
    >> +}
    >> +EXPORT_SYMBOL_GPL(get_fault_pfn);
    >> +
    >> +static pfn_t get_hwpoison_pfn(void)
    >> +{
    >> + return -EHWPOISON;
    >> +}
    >> +
    >
    > Would be better as #defines

    Okay.

    >
    >> int is_hwpoison_pfn(pfn_t pfn)
    >> {
    >> - return pfn == hwpoison_pfn;
    >> + return pfn == -EHWPOISON;
    >> }
    >> EXPORT_SYMBOL_GPL(is_hwpoison_pfn);
    >>
    >> int is_noslot_pfn(pfn_t pfn)
    >> {
    >> - return pfn == bad_pfn;
    >> + return pfn == -ENOENT;
    >> }
    >> EXPORT_SYMBOL_GPL(is_noslot_pfn);
    >>
    >> int is_invalid_pfn(pfn_t pfn)
    >> {
    >> - return pfn == hwpoison_pfn || pfn == fault_pfn;
    >> + return !is_noslot_pfn(pfn) && is_error_pfn(pfn);
    >> }
    >> EXPORT_SYMBOL_GPL(is_invalid_pfn);
    >>
    >
    > So is_*_pfn() could go away and be replaced by ==.
    >

    Okay.

    >>
    >> EXPORT_SYMBOL_GPL(gfn_to_page);
    >>
    >> void kvm_release_page_clean(struct page *page)
    >> {
    >> - kvm_release_pfn_clean(page_to_pfn(page));
    >> + if (!is_error_page(page))
    >> + kvm_release_pfn_clean(page_to_pfn(page));
    >> }
    >> EXPORT_SYMBOL_GPL(kvm_release_page_clean);
    >
    > Note, we can remove calls to kvm_release_page_clean() from error paths
    > now, so in the future we can drop the test.
    >

    Right, since the release path (kvm_release_page_clean) is used in many place
    and on many architectures, i did the change as small as possible for good
    review.

    > Since my comments are better done as a separate patch,

    Yes, i will make a patch to apply all your comments. Thank you, Avi!



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