On Thu, 3 Dec 2015 13:11:40 +0900 Joonsoo Kim <js1304@xxxxxxxxx> wrote: > Until now, COMPACT_CLUSTER_MAX is defined as SWAP_CLUSTER_MAX. > Commit ("mm: increase SWAP_CLUSTER_MAX to batch TLB flushes") > changes SWAP_CLUSTER_MAX from 32 to 256 to improve tlb flush performance > so COMPACT_CLUSTER_MAX is also changed to 256. "mm: increase SWAP_CLUSTER_MAX to batch TLB flushes" has been in limbo for quite a while. Because it has been unclear whether the patch's benefits exceed its costs+risks. We should make a decision here - either do the appropriate testing or drop the patch. > But, it has > no justification on compaction-side and I think that loss is more than > benefit. > > One example is that migration scanner would isolates and migrates > too many pages unnecessarily with 256 COMPACT_CLUSTER_MAX. It may be > enough to migrate 4 pages in order to make order-2 page, but, now, > compaction will migrate 256 pages. > > To reduce this unneeded overhead, this patch restores > COMPACT_CLUSTER_MAX to 32. > > ... > > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -155,7 +155,7 @@ enum { > }; > > #define SWAP_CLUSTER_MAX 256UL > -#define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX > +#define COMPACT_CLUSTER_MAX 32UL > > /* > * Ratio between zone->managed_pages and the "gap" that above the per-zone -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>