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SubjectRe: [PATCH 09/31] mm, vmscan: by default have direct reclaim only shrink once per node
On Fri, Jul 01, 2016 at 09:01:17PM +0100, Mel Gorman wrote:
> Direct reclaim iterates over all zones in the zonelist and shrinking them
> but this is in conflict with node-based reclaim. In the default case,
> only shrink once per node.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> mm/vmscan.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b524d3b72527..34656173a670 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2552,14 +2552,6 @@ static inline bool compaction_ready(struct zone *zone, int order, int classzone_
> * try to reclaim pages from zones which will satisfy the caller's allocation
> * request.
> *
> - * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
> - * Because:
> - * a) The caller may be trying to free *extra* pages to satisfy a higher-order
> - * allocation or
> - * b) The target zone may be at high_wmark_pages(zone) but the lower zones
> - * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
> - * zone defense algorithm.
> - *
> * If a zone is deemed to be full of pinned pages then just give it a light
> * scan then give up on it.
> */
> @@ -2571,6 +2563,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> unsigned long nr_soft_scanned;
> gfp_t orig_mask;
> enum zone_type classzone_idx;
> + pg_data_t *last_pgdat = NULL;
>
> /*
> * If the number of buffer_heads in the machine exceeds the maximum
> @@ -2600,6 +2593,16 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> classzone_idx--;
>
> /*
> + * Shrink each node in the zonelist once. If the zonelist is
> + * ordered by zone (not the default) then a node may be
> + * shrunk multiple times but in that case the user prefers
> + * lower zones being preserved
> + */
> + if (zone->zone_pgdat == last_pgdat)
> + continue;
> + last_pgdat = zone->zone_pgdat;
> +
> + /*

After this change, compaction_ready() which uses zone information
would be called with highest zone in node. So, if some lower zone in
that node is compaction-ready, we cannot stop the reclaim.

Thanks.

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