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    SubjectRe: [PATCH] vmscan: evict use-once pages first (v3)
    Andrew Morton wrote:
    > On Wed, 29 Apr 2009 13:14:36 -0400
    > Rik van Riel <riel@redhat.com> wrote:
    >
    >> When the file LRU lists are dominated by streaming IO pages,
    >> evict those pages first, before considering evicting other
    >> pages.
    >>
    >> This should be safe from deadlocks or performance problems
    >> because only three things can happen to an inactive file page:
    >> 1) referenced twice and promoted to the active list
    >> 2) evicted by the pageout code
    >> 3) under IO, after which it will get evicted or promoted
    >>
    >> The pages freed in this way can either be reused for streaming
    >> IO, or allocated for something else. If the pages are used for
    >> streaming IO, this pageout pattern continues. Otherwise, we will
    >> fall back to the normal pageout pattern.
    >>
    >> ..
    >>
    >> +int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
    >> +{
    >> + unsigned long active;
    >> + unsigned long inactive;
    >> +
    >> + inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
    >> + active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);
    >> +
    >> + return (active > inactive);
    >> +}
    >
    > This function could trivially be made significantly more efficient by
    > changing it to do a single pass over all the zones of all the nodes,
    > rather than two passes.

    How would I do that in a clean way?

    The function mem_cgroup_inactive_anon_is_low and
    the global versions all do the same. It would be
    nice to make all four of them go fast :)

    If there is no standardized infrastructure for
    getting multiple statistics yet, I can probably
    whip something up.

    >> static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
    >> struct zone *zone, struct scan_control *sc, int priority)
    >> {
    >> int file = is_file_lru(lru);
    >>
    >> - if (lru == LRU_ACTIVE_FILE) {
    >> + if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
    >> shrink_active_list(nr_to_scan, zone, sc, priority, file);
    >> return 0;
    >> }
    >
    > And it does get called rather often.

    Same as inactive_anon_is_low.

    Optimizing them might make sense if it turns out to
    use a significant amount of CPU.

    --
    All rights reversed.


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