On 06/28/2012 06:29 AM, Mel Gorman wrote:
Lets say there are two parallel compactions running. Process A meets
the migration PFN and moves to the end of the zone to restart. Process B
finishes scanning mid-way through the zone and updates last_free_pfn. This
will cause Process A to "jump" to where Process B left off which is not
necessarily desirable.
Another side effect is that a workload that allocations/frees
aggressively will not compact as well as the "free" scanner is not
scanning the end of the zone each time. It would be better if
last_free_pfn was updated when a full pageblock was encountered
So;
1. Initialise last_free_pfn to the end of the zone
2. On compaction, scan from last_free_pfn and record where it started
3. If a pageblock is full, update last_free_pfn
4. If the migration and free scanner meet, reset last_free_pfn and
the free scanner. Abort if the free scanner wraps to where it started
Does that make sense?
Yes, that makes sense. We still have to keep track
of whether we have wrapped around, but I guess that
allows for a better name for the bool :)
Maybe cc->wrapped?
Does anyone have a better name?
As for point (4), should we abort when we wrap
around to where we started, or should we abort
when free_pfn and migrate_pfn meet after we
wrapped around?
diff --git a/mm/internal.h b/mm/internal.h
index 2ba87fb..b041874 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -120,6 +120,7 @@ struct compact_control {
unsigned long free_pfn; /* isolate_freepages search base */
unsigned long migrate_pfn; /* isolate_migratepages search base */
bool sync; /* Synchronous migration */
+ bool last_round; /* Last round for order>0 compaction */
I don't get what you mean by last_round. Did you mean "wrapped". When
false, it means the free scanner started from last_pfn and when true it
means it started from last_pfn, met the migrate scanner and wrapped
around to the end of the zone?
Yes, I do mean "wrapped" :)
--
All rights reversed
--
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>