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    SubjectRe: Pagecache: find_or_create_page does not call a proper page allocator function
    On Tue, 24 Apr 2007 18:45:03 +0100 (BST) Hugh Dickins <hugh@veritas.com> wrote:

    > On Tue, 24 Apr 2007, Christoph Lameter wrote:
    > > On Tue, 24 Apr 2007, Hugh Dickins wrote:
    > >
    > > > I've not yet looked at the patch under discussion, but this remark
    > > > prompts me... a couple of days ago I got very worried by the various
    > > > hard-wired GFP_HIGHUSER allocations in mm/migrate.c and mm/mempolicy.c,
    > > > and wondered how those would work out if someone has a blockdev mmap'ed.
    > >
    > > Hmmm.... These not that critical given that 32 bit NUMA systems are a bit
    > > rare.
    >
    > That's true. And everybody but the owners of those systems wish
    > fervently that they didn't exist ;)
    >
    > > And if a page is in the wrong area then it can be bounced before I/O
    > > is performed on it.
    >
    > I think that much is also true, but not where the problem lies.
    > Isn't the problem that filesystems using these block devices
    > expect their metadata to be accessible without kmap calls?
    >

    yup. wherever we dereference buffer_head.b_data we're touching
    page_address(buffer_head.b_page) without kmapping.
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