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    Subject[RFC][PATCH] Fix area->nr_free-- went (-1) issue in buddy system
    Hi all,

    When I setup two zones (NORMAL and DMA) in my system, I got the
    following wired result from /proc/buddyinfo.
    -----------------------------------------------------------------------------------------
    root:~> cat /proc/buddyinfo
    Node 0, zone DMA 2 1 2 1 1 0 0
    1 1 2 2 0 0 0
    Node 0, zone Normal 1 1 1 1 1 1 0
    0 4294967295 0 4294967295 2 0 0
    -----------------------------------------------------------------------------------------

    As you see, two area->nr_free went -1.

    After dig into the code, I found the problem is in the fun
    __free_one_page() when the kernel boot up call free_all_bootmem(). If
    two zones setup, it's possible NORMAL zone merged a block whose order
    =8 at the first time(this time zone[NORMA]->free_area[8].nr_free = 0)
    and found its buddy in the DMA zone. So the two blocks will be merged
    and area->nr_free went to -1.

    My proposed patch is as follows:


    Signed-off-by: Aubrey Li <aubreylee@gmail.com>
    ---------------------------------------------------------------------------------------------------
    --- page_alloc.c.orig 2006-12-19 10:45:25.000000000 +0800
    +++ page_alloc.c 2006-12-19 10:44:48.000000000 +0800
    @@ -407,7 +407,8 @@ static inline void __free_one_page(struc

    list_del(&buddy->lru);
    area = zone->free_area + order;
    - area->nr_free--;
    + if (area->nr_free > 0)
    + area->nr_free--;
    rmv_page_order(buddy);
    combined_idx = __find_combined_index(page_idx, order);
    page = page + (combined_idx - page_idx);
    ----------------------------------------------------------------------------------------------------
    Any comments?
    Thanks,
    -Aubrey
    -
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