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    SubjectRe: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints
    On 02/02/2015 08:55 AM, Mel Gorman wrote:
    > This patch identifies when a thread is frequently calling MADV_DONTNEED
    > on the same region of memory and starts ignoring the hint. On an 8-core
    > single-socket machine this was the impact on ebizzy using glibc 2.19.

    The manpage, at least, claims that we zero-fill after MADV_DONTNEED is
    called:

    > MADV_DONTNEED
    > Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources
    > associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents from the
    > underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file.

    So if we have anything depending on the behavior that it's _always_
    zero-filled after an MADV_DONTNEED, this will break it.


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