Implement a new heap-tuning option: -H

-H alone causes the RTS to use a larger nursery, but without exceeding
the amount of memory that the application is already using.  It trades
off GC time against locality: the default setting is to use a
fixed-size 512k nursery, but this is sometimes worse than using a very
large nursery despite the worse locality.

Not all programs get faster, but some programs that use large heaps do
much better with -H.  e.g. this helps a lot with #3061 (binary-trees),
though not as much as specifying -H<large>.  Typically using -H<large>
is better than plain -H, because the runtime doesn't know ahead of
time how much memory you want to use.

Should -H be on by default?  I'm not sure, it makes some programs go
slower, but others go faster.

1 files changed, 1 insertions, 0 deletions

diff --git a/includes/rts/Flags.h b/includes/rts/Flags.h
index e78bed2d85..b86146148b 100644
--- a/includes/rts/Flags.h
+++ b/includes/rts/Flags.h
@@ -34,6 +34,7 @@ struct GC_FLAGS {
     nat     minAllocAreaSize;   /* in *blocks* */
     nat     minOldGenSize;      /* in *blocks* */
     nat     heapSizeSuggestion; /* in *blocks* */
+    rtsBool heapSizeSuggestionAuto;
     double  oldGenFactor;
     double  pcFreeHeap;