Improve binary garbage collection

The garbage collector in r13b03 is too aggressive in some cases. This
commit raises the level of default initial allowed binary garbage
(virtual heap for binaries) before collecting from 233 words to
46368 words (181 kB on 32-bit).

A new option, min_bin_vheap_size, has been added to spawn_opt,
system_flag and process_flag can be used to change the default values.

The option can also be used with system_info and process_info to
inspect the values.

For symmetry the option min_heap_size has been added to the above
functions where it was previously missing.

Add testcases for min_bin_vheap_size and min_heap_size for
functions process_flag/2, process_info/2, system_info/2 and
spawn_opt/2.

1 files changed, 34 insertions, 12 deletions

diff --git a/erts/emulator/beam/erl_gc.c b/erts/emulator/beam/erl_gc.c
index 363f956b58..e9bf37a173 100644
--- a/erts/emulator/beam/erl_gc.c
+++ b/erts/emulator/beam/erl_gc.c
@@ -2031,23 +2031,45 @@ shrink_new_heap(Process *p, Uint new_sz, Eterm *objv, int nobj)
 }
 
 static Uint
-next_vheap_size(Uint vheap, Uint vheap_sz) {
-    if (vheap < H_MIN_SIZE) {
-    	return H_MIN_SIZE;
-    }
+do_next_vheap_size(Uint vheap, Uint vheap_sz) {
+
+    /*                grow
+     *
+     * vheap_sz ======================
+     *
+     * vheap 75% +    grow
+     *          ----------------------
+     *
+     * vheap 25 - 75% same
+     *          ----------------------
+     *
+     * vheap ~ - 25% shrink
+     *
+     *          ----------------------
+     */
 
-    /* grow */
-    if (vheap > vheap_sz) {
-    	return erts_next_heap_size(2*vheap, 0);
+    if (vheap > (Uint) (vheap_sz*3/4)) {
+
+	while(vheap > (Uint) (vheap_sz*3/4)) {
+	    vheap_sz = vheap_sz*2;
+	}
+
+	return erts_next_heap_size(vheap_sz, 0);
     }
-    /* shrink */
-    if ( vheap < vheap_sz/2) {
-	return (Uint)vheap_sz*3/4;
+
+    if (vheap < (Uint) (vheap_sz/4)) {
+	return erts_next_heap_size((Uint) (vheap_sz / 2), 0);
     }
 
     return vheap_sz;
+
 }
 
+static Uint
+next_vheap_size(Process* p, Uint vheap, Uint vheap_sz) {
+    vheap_sz = do_next_vheap_size(vheap, vheap_sz);
+    return vheap_sz < p->min_vheap_size ? p->min_vheap_size : vheap_sz;
+}
 
 static void
 sweep_proc_externals(Process *p, int fullsweep)
@@ -2250,8 +2272,8 @@ sweep_proc_bins(Process *p, int fullsweep)
         FLAGS(p) |= F_NEED_FULLSWEEP;
     }
 
-    BIN_VHEAP_SZ(p) = next_vheap_size(bin_vheap, BIN_VHEAP_SZ(p));
-    BIN_OLD_VHEAP_SZ(p) = next_vheap_size(BIN_OLD_VHEAP(p), BIN_OLD_VHEAP_SZ(p));
+    BIN_VHEAP_SZ(p) = next_vheap_size(p, bin_vheap, BIN_VHEAP_SZ(p));
+    BIN_OLD_VHEAP_SZ(p) = next_vheap_size(p, BIN_OLD_VHEAP(p), BIN_OLD_VHEAP_SZ(p));
     MSO(p).overhead = bin_vheap;
 
     /*