Date: Tue, 3 Apr 2012 11:18:10 -0400 From: vasanth rao naik sabavat <vasanth.raonaik@gmail.com> To: Mark Tinguely <marktinguely@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: question about amd64 pagetable page allocation. Message-ID: <CAAuizBh0M_wpUvWU%2B0-CMC9XveqQNXOqtB92NhABnGGUVuq4DQ@mail.gmail.com> In-Reply-To: <CAP%2BM-_Es5A3a0%2BcM6K=qi_kbk0ftnHHmZoazuerhg3TxrVr6SA@mail.gmail.com> References: <CAAuizBhUuWvbYjZewO5LgHPuGfi37mW0sJFAKs-YN-G1ZbNAUQ@mail.gmail.com> <CAP%2BM-_Es5A3a0%2BcM6K=qi_kbk0ftnHHmZoazuerhg3TxrVr6SA@mail.gmail.com>
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Hello Mark, Thank you for replying, Could you please point me to any document which illustrates the implementation of recursive page tables in FreeBSD for amd64. Also, I just found that with the following patch from Alon, the usage of vtopte() is removed in pmap_remove_pages(). Why was this removed? http://lists.freebsd.org/pipermail/svn-src-all/2009-March/006006.html Thanks, Vasanth On Tue, Apr 3, 2012 at 10:56 AM, Mark Tinguely <marktinguely@gmail.com>wrote: > 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 > with > > 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 > * > > 0xffffff033c6a0000 > > > > *I would also like to understand the importance of loc_PTmap, I believe > the > > pmap_remove_pages() is derving the page table page addresses from > loc_PTmap? > > (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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