[Xen-devel] confused about the balloon code

[tgh <tianguanhua@xxxxxxxxxx>]

hi
I try to understand the code of balloon ,and got confused about the 
following parts of code:
static int decrease_reservation(unsigned long nr_pages)
{
        ....
       if (!PageHighMem(page)) {
           v = phys_to_virt(pfn << PAGE_SHIFT);
           scrub_pages(v, 1);
           ret = HYPERVISOR_update_va_mapping(
               (unsigned long)v, __pte_ma(0), 0);
           BUG_ON(ret);
       }
#ifdef CONFIG_XEN_SCRUB_PAGES
       else {
           v = kmap(page);
           scrub_pages(v, 1);
           kunmap(page);
       }
#endif
    ....
}

I am confused about the scrub_pages(), what is the meaning of 
scrub_pages, when should we use CONFIG_XEN_SCRUB_PAGES
could you help me
Thanks in advance



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