Date: Tue, 3 Apr 2012 09:56:06 -0500 From: Mark Tinguely <marktinguely@gmail.com> To: vasanth rao naik sabavat <vasanth.raonaik@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: question about amd64 pagetable page allocation. Message-ID: <CAP%2BM-_Es5A3a0%2BcM6K=qi_kbk0ftnHHmZoazuerhg3TxrVr6SA@mail.gmail.com> In-Reply-To: <CAAuizBhUuWvbYjZewO5LgHPuGfi37mW0sJFAKs-YN-G1ZbNAUQ@mail.gmail.com> References: <CAAuizBhUuWvbYjZewO5LgHPuGfi37mW0sJFAKs-YN-G1ZbNAUQ@mail.gmail.com>
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On Tue, Apr 3, 2012 at 8:33 AM, vasanth rao naik sabavat <vasanth.raonaik@gmail.com> wrote: > Hi, > > I am trying to understand the page table page allocation for a process in > FBSD6.1. I see that the page table pages are allocated by vm_page_alloc()= . > I believe the virtual address for this allocated page can be derived by > PHYS_TO_DMAP(VM_PAGE_TO_PHYS(m)), however when I compare this address wit= h > the virtual address accessed in pmap_remove_pages() they are not the same= . > > The virtual address of a *PTE in pmap_remove_pages() is something like > *0xffff800000643200 > * > However, the virtual address of the page allocated by vm_page_alloc() is = =A0* > 0xffffff033c6a0000 > > *I would also like to understand the importance of loc_PTmap, I believe t= he > pmap_remove_pages() is derving the page table page addresses from loc_PTm= ap? > (kgdb) p loc_PTmap > Cannot access memory at address 0xffff800000000000 > > How do we relate the loc_PTmap to the page table pages allocated by > vm_page_alloc() in _pmap_allocpte(). > > Thanks, > Vasanth The answer to your questions will be more obvious when you get an understanding of the Recursive Page Tables. --Mark Tinguely.
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