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    SubjectRe: [RFC 0/4] Transparent on-demand struct page initialization embedded in the buddy allocator
    On Thu, Jul 11, 2013 at 09:03:51PM -0500, Robin Holt wrote:
    > We have been working on this since we returned from shutdown and have
    > something to discuss now. We restricted ourselves to 2MiB initialization
    > to keep the patch set a little smaller and more clear.
    >
    > First, I think I want to propose getting rid of the page flag. If I knew
    > of a concrete way to determine that the page has not been initialized,
    > this patch series would look different. If there is no definitive
    > way to determine that the struct page has been initialized aside from
    > checking the entire page struct is zero, then I think I would suggest
    > we change the page flag to indicate the page has been initialized.

    Ingo or HPA,

    Did I implement this wrong or is there a way to get rid of the page flag
    which is not going to impact normal operation? I don't want to put too
    much more effort into this until I know we are stuck going this direction.
    Currently, the expand() function has a relatively expensive checked
    against the 2MiB aligned pfn's struct page. I do not know of a way to
    eliminate that check against the other page as the first reference we
    see for a page is in the middle of that 2MiB aligned range.

    To identify this as an area of concern, we had booted with a simulator,
    setting watch points on the struct page array region once the
    Uninitialized flag was set and maintaining that until it was cleared.

    Thanks,
    Robin


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