Do RCEC_GC when approaching the max nr of RCEC, not when reaching it.

Otherwise, long running applications still see the max nr of RCEC
slowly growing, which increases the memory usage and
makes the (fixed) contextTab hash table slower to search.
Without this margin, the max could increase as the GC code
is not called at exactly the moment we reach the previous max,
but rather when a thread has run a bunch of basic blocks.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15126

diff --git a/helgrind/libhb_core.c b/helgrind/libhb_core.c
index 6f830bfc8604f8a53d91c850cf453801e4ee608d..a187e28fd065f7293c5f987162d52033f318b983 100644 (file)
--- a/helgrind/libhb_core.c
+++ b/helgrind/libhb_core.c
@@ -6416,13 +6416,19 @@ void libhb_copy_shadow_state ( Thr* thr, Addr src, Addr dst, SizeT len )
 void libhb_maybe_GC ( void )
 {
    /* GC the unreferenced (zero rc) RCECs when
-        (1) reaching a significant nr of RCECs (to avoid scanning a contextTab
-            with mostly NULL ptr)
-    and (2) reaching at least the max nr of RCEC (as we have in any case
-            at least that amount of RCEC in the pool allocator)
-    and (3) the nr of referenced RCECs is less than 75% than total nr RCECs. */
+         (1) reaching a significant nr of RCECs (to avoid scanning a contextTab
+             with mostly NULL ptr)
+     and (2) approaching the max nr of RCEC (as we have in any case
+             at least that amount of RCEC in the pool allocator)
+             Note: the margin allows to avoid a small but constant increase
+             of the max nr of RCEC due to the fact that libhb_maybe_GC is
+             not called when the current nr of RCEC exactly reaches the max.
+     and (3) the nr of referenced RCECs is less than 75% than total nr RCECs.
+     Avoid growing too much the nr of RCEC keeps the memory use low,
+     and avoids to have too many elements in the (fixed) contextTab hashtable.
+   */
    if (UNLIKELY(stats__ctxt_tab_curr > N_RCEC_TAB/2
-                && stats__ctxt_tab_curr >= stats__ctxt_tab_max
+                && stats__ctxt_tab_curr + 1000 >= stats__ctxt_tab_max
                 && stats__ctxt_tab_curr * 0.75 > RCEC_referenced))
       do_RCEC_GC();