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    SubjectRe: [patch] rfc: introduce /dev/hugetlb
    On Sat, 24 Mar 2007 00:11:32 -0700 "Ken Chen" <kenchen@google.com> wrote:

    > On 3/23/07, Andrew Morton <akpm@linux-foundation.org> wrote:
    > > a) Ken observes that obtaining private hugetlb memory via hugetlbfs
    > > involves "fuss".
    > >
    > > b) the libhugetlbfs maintainers then go off and implement a no-fuss way of
    > > doing this.
    >
    > Hmm, what started this thread was libhugetlbfs maintainer complained
    > how "fuss" it was to create private hugetlb mapping and suggested an
    > even bigger kernel change with pagetable_operations API.

    OK. I wasn't paying particularly close attention. But my rant still
    stands ;)

    > The new API
    > was designed with an end goal of introduce /dev/hugetlb (as one of the
    > feature, they might be thinking more). What motivated me here is to
    > point out that we can achieve the same goal of having a /dev/hugetlb
    > with existing hugetlbfs infrastructure and the implementation is
    > relatively straightforward. What it also buys us is a bit more
    > flexibility to the end user who wants to use the interface directly.

    OK.

    Why is it a "fuss" to do this with hugetlbfs files, btw?

    Having read back through the thread, the only substantiation I can really
    see is

    The pagetable_operations API opens up possibilities to do some
    additional (and completely sane) things. For example, I have a patch
    that alters the character device code below to make use of a hugetlb
    ZERO_PAGE. This eliminates almost all the up-front fault time, allowing
    pages to be COW'ed only when first written to. We cannot do things like
    this with hugetlbfs anymore because we have a set of complex semantics to
    preserve.


    Why is this actually a useful feature?

    What does "complex semantics to preserve" mean?


    I dunno. I see a lot of code flying around, but comparatively little
    effort to describe the actual problems which we're trying to solve.

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