On Tue, Mar 23, 2010 at 01:31:43PM -0500, Christoph Lameter wrote: > On Tue, 23 Mar 2010, Mel Gorman wrote: > > > The fragmentation index may indicate that a failure it due to external > > s/it/is/ > Correct. > > fragmentation, a compaction run complete and an allocation failure still > > ??? > I was having some sort of fit when I wrote that obviously. Try this on for size The fragmentation index may indicate that a failure is due to external fragmentation but after a compaction run completes, it is still possible for an allocation to fail. > > fail. There are two obvious reasons as to why > > > > o Page migration cannot move all pages so fragmentation remains > > o A suitable page may exist but watermarks are not met > > > > In the event of compaction and allocation failure, this patch prevents > > compaction happening for a short interval. It's only recorded on the > > compaction is "recorded"? deferred? > deferred makes more sense. What I was thinking at the time was that compact_resume was stored in struct zone - i.e. that is where it is recorded. > > preferred zone but that should be enough coverage. This could have been > > implemented similar to the zonelist_cache but the increased size of the > > zonelist did not appear to be justified. > > > @@ -1787,6 +1787,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order, > > */ > > count_vm_event(COMPACTFAIL); > > > > + /* On failure, avoid compaction for a short time. */ > > + defer_compaction(preferred_zone, jiffies + HZ/50); > > + > > 20ms? How was that interval determined? > Matches the time the page allocator would defer to an event like congestion. The choice is somewhat arbitrary. Ideally, there would be some sort of event that would re-enable compaction but there wasn't an obvious candidate so I used time. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>