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    Subject[PATCH 0/5] mm: rework sys_move_pages() to avoid vmalloc and reduce the overhead
    Hello,

    Here's the first patchset reworking sys_move_pages() as discussed earlier.
    It removes the possibly large vmalloc by using multiple chunks when migrating
    large buffers. It also dramatically increases the throughput for large buffers
    since the lookup in new_page_node() is now limited to a single chunk, causing
    the quadratic complexity to have a much slower impact. There is no need to use
    any radix-tree-like structure to improve this lookup.

    sys_move_pages() duration on a 4-quadcore-opteron 2347HE (1.9Gz), migrating
    between nodes #2 and #3:
    length move_pages (us) move_pages+patch (us)
    4kB 126 98
    40kB 198 168
    400kB 963 937
    4MB 12503 11930
    40MB 246867 11848

    Patches #1 and #4 are the important ones:
    1) stop returning -ENOENT from sys_move_pages() if nothing got migrated
    2) don't vmalloc a huge page_to_node array for do_pages_stat()
    3) extract do_pages_move() out of sys_move_pages()
    4) rework do_pages_move() to work on page_sized chunks
    5) move_pages: no need to set pp->page to ZERO_PAGE(0) by default

    thanks,
    Brice




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