Messages in this thread | | | From | "Aneesh Kumar K.V" <> | Subject | Re: [RFC, PATCH] mm: unified interface to handle page table entries on different levels? | Date | Mon, 19 May 2014 23:46:32 +0530 |
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"Kirill A. Shutemov" <kirill@shutemov.name> writes:
> On Sun, May 18, 2014 at 07:45:59PM -0400, Matthew Wilcox wrote: >> On Sat, May 17, 2014 at 03:33:05AM +0300, Kirill A. Shutemov wrote: >> > Below is my attempt to play with the problem. I've took one function -- >> > page_referenced_one() -- which looks ugly because of different APIs for >> > PTE/PMD and convert it to use vpte_t. vpte_t is union for pte_t, pmd_t >> > and pud_t. >> > >> > Basically, the idea is instead of having different helpers to handle >> > PTE/PMD/PUD, we have one, which take pair of vpte_t + pglevel. >> >> I can't find my original attempt at this now (I am lost in a maze of >> twisted git trees, all subtly different), but I called it a vpe (Virtual >> Page Entry). >> >> Rather than using a pair of vpte_t and pglevel, the vpe_t contained >> enough information to discern what level it was; that's only two bits >> and I think all the architectures have enough space to squeeze in two >> more bits to the PTE (the PMD and PUD obviously have plenty of space). > > I'm not sure if it's possible to find a single free bit on all > architectures. Two is near impossible.
On ppc64 we don't have any free bits.
> > And what about 5-level page tables in future? Will we need 3 bits there? > No way.
-aneesh
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