Messages in this thread | | | Subject | Re: [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes | From | Vlastimil Babka <> | Date | Thu, 28 Apr 2016 10:36:35 +0200 |
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On 04/15/2016 11:13 AM, Mel Gorman wrote: > /* > - * If a zone reaches its high watermark, consider it to be no longer > - * congested. It's possible there are dirty pages backed by congested > - * BDIs but as pressure is relieved, speculatively avoid congestion > - * waits. > + * Fragmentation may mean that the system cannot be rebalanced for > + * high-order allocations. If twice the allocation size has been > + * reclaimed then recheck watermarks only at order-0 to prevent > + * excessive reclaim. Assume that a process requested a high-order > + * can direct reclaim/compact.
Also kcompactd is woken up in this case...
> */ > - if (pgdat_reclaimable(zone->zone_pgdat) && > - zone_balanced(zone, sc->order, false, 0, classzone_idx)) { > - clear_bit(PGDAT_CONGESTED, &pgdat->flags); > - clear_bit(PGDAT_DIRTY, &pgdat->flags); > - } > + if (sc->order && sc->nr_reclaimed >= 2UL << sc->order) > + sc->order = 0; > > return sc->nr_scanned >= sc->nr_to_reclaim;
This looks indeed simpler than my earlier zone_balanced() modification you removed. However I think there's still potential of overreclaim due to a stream of kswapd_wakeups where each will have to reclaim 2UL << sc->order pages, regardless of watermarks. Could be some high-order wakeups from GFP_ATOMIC context that have order-0 fallbacks but will cause kswapd to keep reclaiming when kcompactd can't keep up due to fragmentation...
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