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    SubjectRe: Free memory never fully used, swapping
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    On Fri, 2010-11-26 at 00:15 +0800, Mel Gorman wrote:
    > On Thu, Nov 25, 2010 at 07:51:44PM +0900, KOSAKI Motohiro wrote:
    > > > kswapd is throwing out many times what is needed for the order 3
    > > > watermark to be met. It seems to be not as bad now, but look at these
    > > > pages being reclaimed (200ms intervals, whitespace-packed buddyinfo
    > > > followed by nr_pages_free calculation and final order-3 watermark test,
    > > > kswapd woken after the second sample):
    > > >
    > > > Normal zone at the same time (shown separately for clarity):
    > > >
    > > > Zone order:0 1 2 3 4 5 6 7 8 9 A nr_free or3-low-chk
    > > >
    > > > Normal 452 1 0 0 0 0 0 0 0 0 0 454 -5 <= 238
    > > > Normal 452 1 0 0 0 0 0 0 0 0 0 454 -5 <= 238
    > > > (kswapd wakes)
    > > > Normal 7618 76 0 0 0 0 0 0 0 0 0 7770 145 <= 238
    > > > Normal 8860 73 1 0 0 0 0 0 0 0 0 9010 143 <= 238
    > > > Normal 8929 25 0 0 0 0 0 0 0 0 0 8979 43 <= 238
    > > > Normal 8917 0 0 0 0 0 0 0 0 0 0 8917 -7 <= 238
    > > > Normal 8978 16 0 0 0 0 0 0 0 0 0 9010 25 <= 238
    > > > Normal 9064 4 0 0 0 0 0 0 0 0 0 9072 1 <= 238
    > > > Normal 9068 2 0 0 0 0 0 0 0 0 0 9072 -3 <= 238
    > > > Normal 8992 9 0 0 0 0 0 0 0 0 0 9010 11 <= 238
    > > > Normal 9060 6 0 0 0 0 0 0 0 0 0 9072 5 <= 238
    > > > Normal 9010 0 0 0 0 0 0 0 0 0 0 9010 -7 <= 238
    > > > Normal 8907 5 0 0 0 0 0 0 0 0 0 8917 3 <= 238
    > > > Normal 8576 0 0 0 0 0 0 0 0 0 0 8576 -7 <= 238
    > > > Normal 8018 0 0 0 0 0 0 0 0 0 0 8018 -7 <= 238
    > > > Normal 6778 0 0 0 0 0 0 0 0 0 0 6778 -7 <= 238
    > > > Normal 6189 0 0 0 0 0 0 0 0 0 0 6189 -7 <= 238
    > > > Normal 6220 0 0 0 0 0 0 0 0 0 0 6220 -7 <= 238
    > > > Normal 6096 0 0 0 0 0 0 0 0 0 0 6096 -7 <= 238
    > > > Normal 6251 0 0 0 0 0 0 0 0 0 0 6251 -7 <= 238
    > > > Normal 6127 0 0 0 0 0 0 0 0 0 0 6127 -7 <= 238
    > > > Normal 6218 1 0 0 0 0 0 0 0 0 0 6220 -5 <= 238
    > > > Normal 6034 0 0 0 0 0 0 0 0 0 0 6034 -7 <= 238
    > > > Normal 6065 0 0 0 0 0 0 0 0 0 0 6065 -7 <= 238
    > > > Normal 6189 0 0 0 0 0 0 0 0 0 0 6189 -7 <= 238
    > > > Normal 6189 0 0 0 0 0 0 0 0 0 0 6189 -7 <= 238
    > > > Normal 6096 0 0 0 0 0 0 0 0 0 0 6096 -7 <= 238
    > > > Normal 6127 0 0 0 0 0 0 0 0 0 0 6127 -7 <= 238
    > > > Normal 6158 0 0 0 0 0 0 0 0 0 0 6158 -7 <= 238
    > > > Normal 6127 0 0 0 0 0 0 0 0 0 0 6127 -7 <= 238
    > > > (kswapd sleeps -- maybe too much turkey)
    > > >
    > > > DMA32 get so much reclaimed that the watermark test succeeded long ago.
    > > > Meanwhile, Normal is being reclaimed as well, but because it's fighting
    > > > with allocations, it tries for a while and eventually succeeds (I think),
    > > > but the 200ms samples didn't catch it.
    > > >
    > > > KOSAKI Motohiro, I'm interested in your commit 73ce02e9. This seems
    > > > to be similar to this problem, but your change is not working here.
    > > > We're seeing kswapd run without sleeping, KSWAPD_SKIP_CONGESTION_WAIT
    > > > is increasing (so has_under_min_watermark_zone is true), and pageoutrun
    > > > increasing all the time. This means that balance_pgdat() keeps being
    > > > called, but sleeping_prematurely() is returning true, so kswapd() just
    > > > keeps re-calling balance_pgdat(). If your approach is correct to stop
    > > > kswapd here, the problem seems to be that balance_pgdat's copy of order
    > > > and sc.order is being set to 0, but not pgdat->kswapd_max_order, so
    > > > kswapd never really sleeps. How is this supposed to work?
    > >
    > > Um. this seems regression since commit f50de2d381 (vmscan: have kswapd sleep
    > > for a short interval and double check it should be asleep)
    > >
    >
    > I wrote my own patch before I saw this but for one of the issues we are doing
    > something similar. You are checking if enough pages got reclaimed where as
    > my patch considers any zone being balanced for high-orders being sufficient
    > for kswapd to go to sleep. I think mine is a little stronger because
    > it's checking what state the zones are in for a given order regardless
    > of what has been reclaimed. Lets see what testing has to say.
    record the order seems not sufficient. in balance_pgdat(), the for look
    exit only when:
    priority <0 or sc.nr_reclaimed >= SWAP_CLUSTER_MAX.
    but we do if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
    order = sc.order = 0;
    this means before we set order to 0, we already reclaimed a lot of
    pages, so I thought we need set order to 0 earlier before there are
    enough free pages. below is a debug patch.

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index d31d7ce..ee5d2ed 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2117,6 +2117,26 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    }
    #endif

    +static int all_zone_enough_free_pages(pg_data_t *pgdat)
    +{
    + int i;
    +
    + for (i = 0; i < pgdat->nr_zones; i++) {
    + struct zone *zone = pgdat->node_zones + i;
    +
    + if (!populated_zone(zone))
    + continue;
    +
    + if (zone->all_unreclaimable)
    + continue;
    +
    + if (!zone_watermark_ok(zone, 0, high_wmark_pages(zone) * 8,
    + 0, 0))
    + return 0;
    + }
    + return 1;
    +}
    +
    /* is kswapd sleeping prematurely? */
    static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
    {
    @@ -2355,7 +2375,8 @@ out:
    * back to sleep. High-order users can still perform direct
    * reclaim if they wish.
    */
    - if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
    + if (sc.nr_reclaimed < SWAP_CLUSTER_MAX ||
    + (order > 0 && all_zone_enough_free_pages(pgdat)))
    order = sc.order = 0;

    goto loop_again;



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