Re: [patch 7/8] mm: vmscan: compaction works against zones, not lruvecs

From: Rik van Riel
Date: Wed Dec 12 2012 - 17:33:50 EST

On 12/12/2012 04:43 PM, Johannes Weiner wrote:
The restart logic for when reclaim operates back to back with
compaction is currently applied on the lruvec level. But this does
not make sense, because the container of interest for compaction is a
zone as a whole, not the zone pages that are part of a certain memory

Negative impact is bounded. For one, the code checks that the lruvec
has enough reclaim candidates, so it does not risk getting stuck on a
condition that can not be fulfilled. And the unfairness of hammering
on one particular memory cgroup to make progress in a zone will be
amortized by the round robin manner in which reclaim goes through the
memory cgroups. Still, this can lead to unnecessary allocation
latencies when the code elects to restart on a hard to reclaim or
small group when there are other, more reclaimable groups in the zone.

Move this logic to the zone level and restart reclaim for all memory
cgroups in a zone when compaction requires more free pages from it.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

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