On Fri, 2009-12-04 at 08:09 -0600, Kumar Gala wrote: > On Dec 4, 2009, at 2:58 AM, Benjamin Herrenschmidt wrote: > > > On Fri, 2009-12-04 at 01:18 -0600, Kumar Gala wrote: > >> Ben, David, > >> > >> If we want to support true 4G/4G split on ppc32 using the MSB of the > >> address to determine of the pgd_t is for hugetlbfs isn't going to > >> work. Since every pointer in the pgd_t -> pud_t -> pmd_t is point to > >> at least a 4K page I would think the low order 12-bits should always > >> be 0. > > > > On 32 bit maybe. On 64, the pg/u/md's can be smaller. I don't really > > want to have a different encoding for both types though. > > What do you mean they can be smaller? We have some scenario when we > dont allocate a full page? I agree having the encodings be different > would be bad. I'm trying to avoid having it be different between 32 > bit and 64 (but maybe that will be impossible).
Yes. The intermediary levels are smaller on 64-bit. Also, with hugetlbfs it can create special levels of various sizes depending on the requirements to fit a given huge page size. And that would be true of both 32 and 64-bit in fact. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
