Messages in this thread | | | Subject | Re: [PATCH 05/27] mm, vmscan: Have kswapd only scan based on the highest requested zone | From | Vlastimil Babka <> | Date | Wed, 15 Jun 2016 15:13:13 +0200 |
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On 06/09/2016 08:04 PM, Mel Gorman wrote: > kswapd checks all eligible zones to see if they need balancing even if it was > woken for a lower zone. This made sense when we reclaimed on a per-zone basis > because we wanted to shrink zones fairly so avoid age-inversion problems.
Now we reclaim a single lru, but still will skip over pages from the higher zones than reclaim_idx, so this is not much different from per-zone basis wrt age-inversion?
> Ideally this is completely unnecessary when reclaiming on a per-node basis. > In theory, there may still be anomalies when all requests are for lower > zones and very old pages are preserved in higher zones but this should be > the exceptional case. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
I don't see the argument, but agree it should be exceptional in any case, and if there's such a case, it's better to focus on pages from the zone(s) where a pending (potentially atomic) allocation is restricted to. Or rather, this is the only way we can focus reclaim on such pages now that there's a single lru list.
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> --- > mm/vmscan.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index ab1b28e7e20a..0a619241c576 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3171,11 +3171,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) > > sc.nr_reclaimed = 0; > > - /* > - * Scan in the highmem->dma direction for the highest > - * zone which needs scanning > - */ > - for (i = pgdat->nr_zones - 1; i >= 0; i--) { > + /* Scan from the highest requested zone to dma */ > + for (i = classzone_idx; i >= 0; i--) { > struct zone *zone = pgdat->node_zones + i; > > if (!populated_zone(zone)) >
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