Messages in this thread | | | Date | Tue, 29 Mar 2005 21:50:56 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH 1/6] freepgt: free_pgtables use vma list |
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On Wed, 23 Mar 2005, David S. Miller wrote: > On Wed, 23 Mar 2005 11:16:27 -0800 > "Luck, Tony" <tony.luck@intel.com> wrote: > > > Can we legislate that "end==0" isn't possible. > > It is possible with some out-of-tree patches. > > I could certainly support it on sparc64, the only > glitch is that this is where the virtually mapped > linear page tables sit right now :-)
Though my knowledge of out-of-tree patches is very limited, I believe "end == 0" is not possible on any arch - when "end" originates from vma->vm_end (or vm_struct->addr + size). There are plenty of "BUG_ON(addr >= end)"s dotted around to support that, and other places that would be confused by vm_start > vm_end.
(And when Linus first proposed the sysenter page at 0xfffff000, I protested, and he brought it down to 0xffffe000: I think we'll do well ever to keep that last virtual page invalid.)
But certainly "ceiling == 0" is possible and common, and "rounded-up end" may well be 0 with out-of-tree patches. When I did those free_pgtables tests, it seemed simpler to treat "end" in the same way as "ceiling", implicitly allowing it the 0 case. Perhaps that's not so in Nick's version, I've yet to think through it.
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