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    SubjectRe: FW: [PATCH] powerpc/mm: Export HPAGE_SHIFT
    On Wed, 04 Feb 2009 12:50:48 +1100 Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

    > On Tue, 2009-02-03 at 17:08 -0800, Roland Dreier wrote:
    > > Forwarding Eli's patch below, since PowerPC guys may have missed it. I
    > > guess the question for Ben et al is whether there is any issue with
    > > exporting HPAGE_SHIFT for modules (can be EXPORT_SYMBOL_GPL if you feel
    > > it's an internal detail). It would probably make sense to roll this
    > > change into the mlx4 change that Eli alludes to below and merge through
    > > my tree (with ppc maintainer acks of course), rather than splitting this
    > > patch out and introducing cross-tree dependencies (and also separating
    > > the rationale for the change from the change itself).
    > >
    > > Thanks,
    > > Roland
    > >
    > >
    > > Drivers may want to take advantage of the large pages used for memory obtained
    > > from hugetlbfs. One example is mlx4_ib which can use much less MTT entries (in
    > > the order of HPAGE_SIZE / PAGE_SIZE) when registering such memory, thus scale
    > > significantly better when registering larger memory regions. Other drivers
    > > could also benefit from this.
    >
    > Except that we support multiple large page sizes nowadays ... I think
    > the size can be specified per mountpoint of hugetlbfs no ? Thus things
    > like mellanox would have to query the page size used for a given
    > mapping.
    >
    > Do the generic hugetlbfs code provides such an API ? If not, we may need
    > to add one.
    >

    I think it's something like

    huge_page_size(page_hstate(page))



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