mm, compaction: restrict fragindex to costly orders

Fragmentation index and the vm.extfrag_threshold sysctl is meant as a
heuristic to prevent excessive compaction for costly orders (i.e.  THP).
It's unlikely to make any difference for non-costly orders, especially
with the default threshold.  But we cannot afford any uncertainty for
the non-costly orders where the only alternative to successful
reclaim/compaction is OOM.  After the recent patches we are guaranteed
maximum effort without heuristics from compaction before deciding OOM,
and fragindex is the last remaining heuristic.  Therefore skip fragindex
altogether for non-costly orders.

Suggested-by: Michal Hocko <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions