Experimental "mark-region" strategy for the old generation

Sometimes better than the default copying, enabled by +RTS -w

1 files changed, 82 insertions, 0 deletions

diff --git a/rts/sm/Sweep.c b/rts/sm/Sweep.c
new file mode 100644
index 0000000000..979fe9ccea
--- /dev/null
+++ b/rts/sm/Sweep.c
@@ -0,0 +1,82 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team 2008 
+ *
+ * Simple mark/sweep, collecting whole blocks.
+ *
+ * Documentation on the architecture of the Garbage Collector can be
+ * found in the online commentary:
+ * 
+ *   http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
+ *
+ * ---------------------------------------------------------------------------*/
+
+#include "Rts.h"
+#include "Sweep.h"
+#include "Block.h"
+#include "Trace.h"
+
+void
+sweep(step *step)
+{
+    bdescr *bd, *prev, *next;
+    nat i;
+    nat freed, resid, fragd, blocks, live;
+    
+    ASSERT(countBlocks(step->old_blocks) == step->n_old_blocks);
+
+    live = 0; // estimate of live data in this gen
+    freed = 0;
+    fragd = 0;
+    blocks = 0;
+    prev = NULL;
+    for (bd = step->old_blocks; bd != NULL; bd = next)
+    {
+        next = bd->link;
+
+        if (!(bd->flags & BF_MARKED)) { 
+            prev = bd;
+            continue;
+        }
+
+        blocks++;
+        resid = 0;
+        for (i = 0; i < BLOCK_SIZE_W / BITS_IN(W_); i++)
+        {
+            if (bd->u.bitmap[i] != 0) resid++;
+        }
+        live += resid * BITS_IN(W_);
+
+        if (resid == 0)
+        {
+            freed++;
+            step->n_old_blocks--;
+            if (prev == NULL) {
+                step->old_blocks = next;
+            } else {
+                prev->link = next;
+            }
+            freeGroup(bd);
+        }
+        else
+        {
+            prev = bd;
+            if (resid < (BLOCK_SIZE_W * 3) / (BITS_IN(W_) * 4)) {
+                fragd++;
+                bd->flags |= BF_FRAGMENTED;
+            }
+        }
+    }
+
+    step->live_estimate = live;
+
+    trace(DEBUG_gc|TRACE_gc, "sweeping: %d blocks, %d were copied, %d freed (%d%%), %d are fragmented, live estimate: %d%%",
+          step->n_old_blocks + freed,
+          step->n_old_blocks - blocks + freed,
+          freed,
+          blocks == 0 ? 0 : (freed * 100) / blocks,
+          fragd, 
+          (blocks - freed) == 0 ? 0 : ((live / BLOCK_SIZE_W) * 100) / (blocks - freed));
+
+    ASSERT(countBlocks(step->old_blocks) == step->n_old_blocks);
+}