Messages in this thread | | | Subject | Re: [RFC 5/7] LTTng instrumentation mm | From | Dave Hansen <> | Date | Mon, 19 Nov 2007 10:07:05 -0800 |
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On Fri, 2007-11-16 at 09:47 -0500, Mathieu Desnoyers wrote: > * Dave Hansen (haveblue@us.ibm.com) wrote: > > For most (all?) architectures, the PFN and the virtual address in the > > kernel's linear are interchangeable with pretty trivial arithmetic. All > > pages have a pfn, but not all have a virtual address. Thus, I suggested > > using the pfn. What kind of virtual addresses are you talking about? > > > > Hrm, in asm-generic/memory_model.h, we have various versions of > __page_to_pfn. Normally they all cast the result to (unsigned long), > except for : > > > #elif defined(CONFIG_SPARSEMEM_VMEMMAP) > > /* memmap is virtually contigious. */ > #define __pfn_to_page(pfn) (vmemmap + (pfn)) > #define __page_to_pfn(page) ((page) - vmemmap) > > So I guess the result is a pointer ? Should this be expected ?
Nope. 'pointer - pointer' is an integer. Just solve this equation for integer:
'pointer + integer = pointer'
-- Dave
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