Fix a mistake in calculating min nursery. Change default min nursery on

64 bits back to 2m (from 20m)

Author: qinsoon

src/util/heap/gc_trigger.rs

@@ -147,7 +147,7 @@ impl<VM: VMBinding> GCTrigger<VM> {
                 let min_bytes = conversions::raw_align_up(min_bytes as usize, BYTES_IN_PAGE);
                 if min_bytes < DEFAULT_MIN_NURSERY {
                     warn!("Proportional nursery with min size {} ({}) is smaller than DEFAULT_MIN_NURSERY ({}). Use DEFAULT_MIN_NURSERY instead.", min, min_bytes, DEFAULT_MIN_NURSERY);
-                    DEFAULT_MAX_NURSERY
+                    DEFAULT_MIN_NURSERY
                 } else {
                     min_bytes
                 }

src/util/options.rs

@@ -101,7 +101,7 @@ impl FromStr for PerfEventOptions {
 /// The default min nursery size. This does not affect the actual space we create as nursery. It is
 /// only used in the GC trigger check.
 #[cfg(target_pointer_width = "64")]
-pub const DEFAULT_MIN_NURSERY: usize = 20 << LOG_BYTES_IN_MBYTE;
+pub const DEFAULT_MIN_NURSERY: usize = 2 << LOG_BYTES_IN_MBYTE;
 /// The default max nursery size. This does not affect the actual space we create as nursery. It is
 /// only used in the GC trigger check.
 #[cfg(target_pointer_width = "64")]