On Tue, Jan 10, 2017 at 01:55:51PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> get_scan_count considers the whole node LRU size when
> - doing SCAN_FILE due to many page cache inactive pages
> - calculating the number of pages to scan
>
> in both cases this might lead to unexpected behavior especially on 32b
> systems where we can expect lowmem memory pressure very often.
The amount of retrofitting zones back into reclaim is disappointing :/
> /*
> + * Return the number of pages on the given lru which are eligible for the
> + * given zone_idx
> + */
> +static unsigned long lruvec_lru_size_eligibe_zones(struct lruvec *lruvec,
> + enum lru_list lru, int zone_idx)
> +{
> + struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> + unsigned long lru_size;
> + int zid;
> +
> + lru_size = lruvec_lru_size(lruvec, lru);
> + for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
> + struct zone *zone = &pgdat->node_zones[zid];
> + unsigned long size;
> +
> + if (!managed_zone(zone))
> + continue;
> +
> + size = lruvec_zone_lru_size(lruvec, lru, zid);
> + lru_size -= min(size, lru_size);
> + }
> +
> + return lru_size;
The only other use of lruvec_lru_size() is also in get_scan_count(),
where it decays the LRU pressure balancing ratios. That caller wants
to operate on the entire lruvec.
Can you instead add the filtering logic to lruvec_lru_size() directly,
and pass MAX_NR_ZONES when operating on the entire lruvec? That would
make the code quite a bit clearer than having 3 different lruvec size
querying functions.
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