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    SubjectRe: Free memory never fully used, swapping
    Date
    > On Fri, 2010-11-26 at 10:31 +0800, KOSAKI Motohiro wrote:
    > > > 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.
    > Yes, this will break high order reclaim, but we need a compromise.
    > wrongly reclaim pages is more worse. could increase the watermark in
    > all_zone_enough_free_pages() better?
    >

    Hmm..
    I guess I haven't catch your mention. you wrote

    > > > 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

    and I wrote it's not a lot. So, I don't understand why you are talking
    about watermark increasing now. Personally you seems to talk unrelated
    topic. Can you please elablate your point more?








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