On Thu, Jun 28, 2012 at 01:55:20PM -0400, Rik van Riel wrote: > Order > 0 compaction stops when enough free pages of the correct > page order have been coalesced. When doing subsequent higher order > allocations, it is possible for compaction to be invoked many times. > > However, the compaction code always starts out looking for things to > compact at the start of the zone, and for free pages to compact things > to at the end of the zone. > > This can cause quadratic behaviour, with isolate_freepages starting > at the end of the zone each time, even though previous invocations > of the compaction code already filled up all free memory on that end > of the zone. > > This can cause isolate_freepages to take enormous amounts of CPU > with certain workloads on larger memory systems. > > The obvious solution is to have isolate_freepages remember where > it left off last time, and continue at that point the next time > it gets invoked for an order > 0 compaction. This could cause > compaction to fail if cc->free_pfn and cc->migrate_pfn are close > together initially, in that case we restart from the end of the > zone and try once more. > > Forced full (order == -1) compactions are left alone. > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> > Reported-by: Jim Schutt <jaschut@xxxxxxxxxx> > Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> > --- > v2: implement Mel's suggestions, handling wrap-around etc > I have not tested it myself but it looks correct! Thanks very much. Acked-by: Mel Gorman <mel@xxxxxxxxx> -- Mel Gorman SUSE Labs -- 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>