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    Subjectvmscan.c heuristic adjustment for smaller systems
    Marc Singer reported an issue where an embedded ARM system performed
    poorly due to page replacement potentially prematurely replacing
    mapped memory where there was very little mapped pagecache in use to
    begin with.

    The following patch attempts to address the issue by using the
    _maximum_ of vm_swappiness and distress to add to the mapped ratio, so
    that distress doesn't contribute to swap_tendency until it exceeds
    vm_swappiness, and afterward the effect is not cumulative.

    The intended effect is that swap_tendency should vary in a more jagged
    way, and not be elevated by distress beyond vm_swappiness until distress
    exceeds vm_swappiness. For instance, since distress is 100 >>
    zone->prev_priority, no distinction is made between a vm_swappiness of
    50 or a vm_swappiness of 90 given the same mapped_ratio.

    Marc Singer has results where this is an improvement, and hopefully can
    clarify as-needed. Help determining whether this policy change is an
    improvement for a broader variety of systems would be appreciated.

    -- wli

    Index: singer-2.6.5-mm6/mm/vmscan.c
    --- singer-2.6.5-mm6.orig/mm/vmscan.c 2004-04-14 23:21:19.000000000 -0700
    +++ singer-2.6.5-mm6/mm/vmscan.c 2004-04-17 11:09:35.000000000 -0700
    @@ -636,7 +636,7 @@
    * A 100% value of vm_swappiness overrides this algorithm altogether.
    - swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
    + swap_tendency = mapped_ratio / 2 + max(distress, vm_swappiness);

    * Now use this metric to decide whether to start moving mapped memory
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