Re: [RFC 08/13] mm, compaction: simplify contended compaction handling

[Vlastimil Babka]

On 05/13/2016 03:09 PM, Michal Hocko wrote:
> > >@@ -1564,14 +1564,11 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
> > >  	trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
> > >  				cc->free_pfn, end_pfn, sync, ret);
> > >
> > >-	if (ret == COMPACT_CONTENDED)
> > >-		ret = COMPACT_PARTIAL;
> > >-
> > >  	return ret;
> > >  }
> This took me a while to grasp but then I realized this is correct
> because we shouldn't pretend progress when there was none in fact,
> especially when __alloc_pages_direct_compact basically replaced this
> "fake" COMPACT_PARTIAL by COMPACT_CONTENDED anyway.

Yes. Actually COMPACT_CONTENDED compact_result used to be just for the 
tracepoint, and __alloc_pages_direct_compact used another function 
parameter to signal contention. You changed it with the oom rework so 
COMPACT_CONTENDED result value was used, so this hunk just makes sure 
it's still reported correctly.