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    SubjectRe: [PATCH 10 of 20] ipath - support for userspace apps using core driver

    On Fri, 17 Mar 2006, Bryan O'Sullivan wrote:
    > Hmm. Which of the implementations that you've seen will return
    > something not backed by a struct page? On the half dozen arches I've
    > looked at (i386/x86_64, powerpc, sparc64, ia64, mips), every one uses
    > either kmalloc, __get_free_pages, or __alloc_pages at some point, and I
    > think they all have struct pages behind them.

    kmalloc may be backed by a "struct page", but the point is that it does
    not honor the page _count_, and as such it is totally unsuitable for any
    VM usage.

    The VM relies on the page count very fundamentally, so by doing a
    "get_page()" you'll tell every other user that you have a reference to a
    page, and it won't be free'd until all references are gone. In contrast,
    if you do a "get_page()" on something that has been allocated with
    kmalloc(), the slab code will totally ignore it, and happily re-allocate
    it to something else once the _original_ allocator free's it.

    So kmalloc() really isn't appropriate.

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      Last update: 2009-11-18 23:46    [W:0.020 / U:13.976 seconds]
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