tree c0395d9cf775fd9225e81b055fc8f5540a14333a
parent e42c8ff2999de1239a57d434bfbd8e9f2a56e814
author Mel Gorman <mgorman@suse.de> 1353460703 +0000
committer Mel Gorman <mgorman@suse.de> 1355236975 +0000

mm: sched: Adapt the scanning rate if a NUMA hinting fault does not migrate

The PTE scanning rate and fault rates are two of the biggest sources of
system CPU overhead with automatic NUMA placement.  Ideally a proper policy
would detect if a workload was properly placed, schedule and adjust the
PTE scanning rate accordingly. We do not track the necessary information
to do that but we at least know if we migrated or not.

This patch scans slower if a page was not migrated as the result of a
NUMA hinting fault up to sysctl_numa_balancing_scan_period_max which is
now higher than the previous default. Once every minute it will reset
the scanner in case of phase changes.

This is hilariously crude and the numbers are arbitrary. Workloads will
converge quite slowly in comparison to what a proper policy should be able
to do. On the plus side, we will chew up less CPU for workloads that have
no need for automatic balancing.

Signed-off-by: Mel Gorman <mgorman@suse.de>