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    SubjectRe: Free memory never fully used, swapping
    Date
    > 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;

    Ummm. this doesn't work. this place is processed every 32 pages reclaimed.
    (see below code and comment). Theresore your patch break high order reclaim
    logic.


    /*
    * We do this so kswapd doesn't build up large priorities for
    * example when it is freeing in parallel with allocators. It
    * matches the direct reclaim path behaviour in terms of impact
    * on zone->*_priority.
    */
    if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
    break;

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