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    Subject[PATCH 04/14] readahead: thrashing recovery method: check unbalanced aging
    Always check for unbalanced aging in thrashing_recovery_readahead(), and
    account RA_EVENT_READAHEAD_MUTILATE/RA_EVENT_READAHEAD_THRASHING events.

    Unbalanced zone/node aging can come from abnormal system loads, or
    misconfigured NUMA policies.

    Thrashings are rare events, hence the cost of probe_page() is not a concern.

    Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
    ---
    mm/readahead.c | 11 ++++-------
    1 file changed, 4 insertions(+), 7 deletions(-)

    --- linux-2.6.21-rc3-mm2.orig/mm/readahead.c
    +++ linux-2.6.21-rc3-mm2/mm/readahead.c
    @@ -1546,14 +1546,11 @@ thrashing_recovery_readahead(struct addr
    pgoff_t offset, unsigned long ra_max)
    {
    unsigned long ra_size;
    + int unbalanced_aging = probe_page(mapping, offset - 1);

    -#ifdef CONFIG_DEBUG_READAHEAD
    - if (probe_page(mapping, offset - 1))
    - ra_account(ra, RA_EVENT_READAHEAD_MUTILATE,
    - ra->readahead_index - offset);
    - ra_account(ra, RA_EVENT_READAHEAD_THRASHING,
    - ra->readahead_index - offset);
    -#endif
    + ra_account(ra, unbalanced_aging ? RA_EVENT_READAHEAD_MUTILATE :
    + RA_EVENT_READAHEAD_THRASHING,
    + ra->readahead_index - offset);

    if (offset < ra->ra_index) {
    /*
    --
    -
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