[Xen-devel] a question about count_info

["strongerwill" <strongerwill@xxxxxxxxx>]

Hi guys:

   I am working on Xen 4.0.0. In my project, I need to know the reference number of a paticular page. But I found the result do not match what I think. I need your help.

 

For example, I allocate a buffer in kernel (dom0)

char * buf = kmalloc( 4096, ...);

Then I use my designed hypercall to read the count_info like this way:

// add is the location of the buffer

l1_pgentry_t nl1e = guest_map_l1e(current, add, &tmp);

                unsigned long pfn = 0, mfn = 0;

                p2m_type_t p2mt = 0;

                struct page_info *page = NULL;

                pfn = l1e_get_pfn(nl1e);

                mfn = mfn_x( gfn_to_mfn( current->domain, pfn, &p2mt ) );

                debug_trace(printk("pfn %lx, mfn %lx, p2mt %x nl1e.l1 %llx\n", pfn, mfn, p2mt, nl1e.l1));

// here I check the validation of mfn, then try to get page

                page = mfn_to_page(mfn);

                debug_trace(printk("page count %lx, marked count %lx, page typeinfo %lx\n",

                        page->count_info, page->count_info & PGC_count_mask, page->u.inuse.type_info));

 

the output likes this:

 

pfn 5a4d0, mfn 5a4d0, p2mt 1  nl1e.l1 800000005a4d0063 

page count 80000002, marked count 2, page typeinfo 74000001

 

When I allocate memory using vmalloc

the output likes this:

 

pfn 351ed, mfn 351ed, p2mt 1 nl1e.l1 80000000351ed063

page count 80000003, marked count 3, page typeinfo 74000002

 

previously I think the referece number (count_info) of  these new allocated buffers should be "1". Now the output confuses me. Any one can explain this?

Thanks very much

 

 

Yueqiang

 

2010-08-05

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strongerwill

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