X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fsm%2FScav.c;h=4fa0a220e0dc8a8ff74d436f4baba6f2d3585691;hb=4207605cc8e035e05f651334ef1be90b098d305d;hp=b8fb54bfcd38ce4d397b1e30f1ac5258793fbe2c;hpb=aceacfc45ac040b450e36626723d63cd1977ecee;p=ghc-hetmet.git

diff --git a/rts/sm/Scav.c b/rts/sm/Scav.c
index b8fb54b..4fa0a22 100644
--- a/rts/sm/Scav.c
+++ b/rts/sm/Scav.c
@@ -11,20 +11,22 @@
  *
  * ---------------------------------------------------------------------------*/
 
+#include "PosixSource.h"
 #include "Rts.h"
-#include "RtsFlags.h"
+
 #include "Storage.h"
-#include "MBlock.h"
 #include "GC.h"
 #include "GCThread.h"
 #include "GCUtils.h"
 #include "Compact.h"
+#include "MarkStack.h"
 #include "Evac.h"
 #include "Scav.h"
 #include "Apply.h"
 #include "Trace.h"
-#include "LdvProfile.h"
 #include "Sanity.h"
+#include "Capability.h"
+#include "LdvProfile.h"
 
 static void scavenge_stack (StgPtr p, StgPtr stack_end);
 
@@ -36,7 +38,9 @@ static void scavenge_large_bitmap (StgPtr p,
 # define evacuate(a) evacuate1(a)
 # define recordMutableGen_GC(a,b) recordMutableGen(a,b)
 # define scavenge_loop(a) scavenge_loop1(a)
-# define scavenge_mutable_list(g) scavenge_mutable_list1(g)
+# define scavenge_block(a) scavenge_block1(a)
+# define scavenge_mutable_list(bd,g) scavenge_mutable_list1(bd,g)
+# define scavenge_capability_mut_lists(cap) scavenge_capability_mut_Lists1(cap)
 #endif
 
 /* -----------------------------------------------------------------------------
@@ -67,6 +71,13 @@ scavengeTSO (StgTSO *tso)
         return;
     }
 
+    debugTrace(DEBUG_gc,"scavenging thread %d",(int)tso->id);
+
+    // update the pointer from the Task.
+    if (tso->bound != NULL) {
+        tso->bound->tso = tso;
+    }
+
     saved_eager = gct->eager_promotion;
     gct->eager_promotion = rtsFalse;
 
@@ -85,10 +96,10 @@ scavengeTSO (StgTSO *tso)
     scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
 
     if (gct->failed_to_evac) {
-        tso->flags |= TSO_DIRTY;
+        tso->dirty = 1;
         scavenge_TSO_link(tso);
     } else {
-        tso->flags &= ~TSO_DIRTY;
+        tso->dirty = 0;
         scavenge_TSO_link(tso);
         if (gct->failed_to_evac) {
             tso->flags |= TSO_LINK_DIRTY;
@@ -256,7 +267,7 @@ scavenge_srt (StgClosure **srt, nat srt_bitmap)
 	  // If the SRT entry hasn't got bit 0 set, the SRT entry points to a
 	  // closure that's fixed at link-time, and no extra magic is required.
 	  if ( (unsigned long)(*srt) & 0x1 ) {
-	      evacuate(stgCast(StgClosure**,(stgCast(unsigned long, *srt) & ~0x1)));
+	      evacuate( (StgClosure**) ((unsigned long) (*srt) & ~0x1));
 	  } else {
 	      evacuate(p);
 	  }
@@ -295,11 +306,11 @@ scavenge_fun_srt(const StgInfoTable *info)
 /* -----------------------------------------------------------------------------
    Scavenge a block from the given scan pointer up to bd->free.
 
-   evac_step is set by the caller to be either zero (for a step in a
+   evac_gen is set by the caller to be either zero (for a step in a
    generation < N) or G where G is the generation of the step being
    scavenged.  
 
-   We sometimes temporarily change evac_step back to zero if we're
+   We sometimes temporarily change evac_gen back to zero if we're
    scavenging a mutable object where eager promotion isn't such a good
    idea.  
    -------------------------------------------------------------------------- */
@@ -309,20 +320,20 @@ scavenge_block (bdescr *bd)
 {
   StgPtr p, q;
   StgInfoTable *info;
-  step *saved_evac_step;
+  generation *saved_evac_gen;
   rtsBool saved_eager_promotion;
-  step_workspace *ws;
+  gen_workspace *ws;
 
-  debugTrace(DEBUG_gc, "scavenging block %p (gen %d, step %d) @ %p",
-	     bd->start, bd->gen_no, bd->step->no, bd->u.scan);
+  debugTrace(DEBUG_gc, "scavenging block %p (gen %d) @ %p",
+	     bd->start, bd->gen_no, bd->u.scan);
 
   gct->scan_bd = bd;
-  gct->evac_step = bd->step;
-  saved_evac_step = gct->evac_step;
+  gct->evac_gen = bd->gen;
+  saved_evac_gen = gct->evac_gen;
   saved_eager_promotion = gct->eager_promotion;
   gct->failed_to_evac = rtsFalse;
 
-  ws = &gct->steps[bd->step->abs_no];
+  ws = &gct->gens[bd->gen->no];
 
   p = bd->u.scan;
   
@@ -331,6 +342,7 @@ scavenge_block (bdescr *bd)
   // time around the loop.
   while (p < bd->free || (bd == ws->todo_bd && p < ws->todo_free)) {
 
+      ASSERT(bd->link == NULL);
     ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
     info = get_itbl((StgClosure *)p);
     
@@ -504,8 +516,6 @@ scavenge_block (bdescr *bd)
 	break;
 
     case CAF_BLACKHOLE:
-    case SE_CAF_BLACKHOLE:
-    case SE_BLACKHOLE:
     case BLACKHOLE:
 	p += BLACKHOLE_sizeW();
 	break;
@@ -601,11 +611,11 @@ scavenge_block (bdescr *bd)
     case TVAR_WATCH_QUEUE:
       {
 	StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-	gct->evac_step = 0;
+	gct->evac_gen = 0;
 	evacuate((StgClosure **)&wq->closure);
 	evacuate((StgClosure **)&wq->next_queue_entry);
 	evacuate((StgClosure **)&wq->prev_queue_entry);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	p += sizeofW(StgTVarWatchQueue);
 	break;
@@ -614,10 +624,10 @@ scavenge_block (bdescr *bd)
     case TVAR:
       {
 	StgTVar *tvar = ((StgTVar *) p);
-	gct->evac_step = 0;
+	gct->evac_gen = 0;
 	evacuate((StgClosure **)&tvar->current_value);
 	evacuate((StgClosure **)&tvar->first_watch_queue_entry);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	p += sizeofW(StgTVar);
 	break;
@@ -626,11 +636,11 @@ scavenge_block (bdescr *bd)
     case TREC_HEADER:
       {
         StgTRecHeader *trec = ((StgTRecHeader *) p);
-        gct->evac_step = 0;
+        gct->evac_gen = 0;
 	evacuate((StgClosure **)&trec->enclosing_trec);
 	evacuate((StgClosure **)&trec->current_chunk);
 	evacuate((StgClosure **)&trec->invariants_to_check);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	p += sizeofW(StgTRecHeader);
         break;
@@ -641,14 +651,14 @@ scavenge_block (bdescr *bd)
 	StgWord i;
 	StgTRecChunk *tc = ((StgTRecChunk *) p);
 	TRecEntry *e = &(tc -> entries[0]);
-	gct->evac_step = 0;
+	gct->evac_gen = 0;
 	evacuate((StgClosure **)&tc->prev_chunk);
 	for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
 	  evacuate((StgClosure **)&e->tvar);
 	  evacuate((StgClosure **)&e->expected_value);
 	  evacuate((StgClosure **)&e->new_value);
 	}
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	p += sizeofW(StgTRecChunk);
 	break;
@@ -657,10 +667,10 @@ scavenge_block (bdescr *bd)
     case ATOMIC_INVARIANT:
       {
         StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-        gct->evac_step = 0;
+        gct->evac_gen = 0;
 	evacuate(&invariant->code);
 	evacuate((StgClosure **)&invariant->last_execution);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	p += sizeofW(StgAtomicInvariant);
         break;
@@ -669,11 +679,11 @@ scavenge_block (bdescr *bd)
     case INVARIANT_CHECK_QUEUE:
       {
         StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-        gct->evac_step = 0;
+        gct->evac_gen = 0;
 	evacuate((StgClosure **)&queue->invariant);
 	evacuate((StgClosure **)&queue->my_execution);
 	evacuate((StgClosure **)&queue->next_queue_entry);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	p += sizeofW(StgInvariantCheckQueue);
         break;
@@ -694,7 +704,7 @@ scavenge_block (bdescr *bd)
     if (gct->failed_to_evac) {
 	gct->failed_to_evac = rtsFalse;
 	if (bd->gen_no > 0) {
-	    recordMutableGen_GC((StgClosure *)q, &generations[bd->gen_no]);
+	    recordMutableGen_GC((StgClosure *)q, bd->gen_no);
 	}
     }
   }
@@ -732,14 +742,12 @@ scavenge_mark_stack(void)
 {
     StgPtr p, q;
     StgInfoTable *info;
-    step *saved_evac_step;
+    generation *saved_evac_gen;
 
-    gct->evac_step = &oldest_gen->steps[0];
-    saved_evac_step = gct->evac_step;
+    gct->evac_gen = oldest_gen;
+    saved_evac_gen = gct->evac_gen;
 
-linear_scan:
-    while (!mark_stack_empty()) {
-	p = pop_mark_stack();
+    while ((p = pop_mark_stack())) {
 
 	ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
 	info = get_itbl((StgClosure *)p);
@@ -881,8 +889,6 @@ linear_scan:
 	}
 
 	case CAF_BLACKHOLE:
-	case SE_CAF_BLACKHOLE:
-	case SE_BLACKHOLE:
 	case BLACKHOLE:
 	case ARR_WORDS:
 	    break;
@@ -971,11 +977,11 @@ linear_scan:
 	case TVAR_WATCH_QUEUE:
 	  {
 	    StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-	    gct->evac_step = 0;
+	    gct->evac_gen = 0;
             evacuate((StgClosure **)&wq->closure);
 	    evacuate((StgClosure **)&wq->next_queue_entry);
 	    evacuate((StgClosure **)&wq->prev_queue_entry);
-	    gct->evac_step = saved_evac_step;
+	    gct->evac_gen = saved_evac_gen;
 	    gct->failed_to_evac = rtsTrue; // mutable
 	    break;
 	  }
@@ -983,10 +989,10 @@ linear_scan:
 	case TVAR:
 	  {
 	    StgTVar *tvar = ((StgTVar *) p);
-	    gct->evac_step = 0;
+	    gct->evac_gen = 0;
 	    evacuate((StgClosure **)&tvar->current_value);
 	    evacuate((StgClosure **)&tvar->first_watch_queue_entry);
-	    gct->evac_step = saved_evac_step;
+	    gct->evac_gen = saved_evac_gen;
 	    gct->failed_to_evac = rtsTrue; // mutable
 	    break;
 	  }
@@ -996,14 +1002,14 @@ linear_scan:
 	    StgWord i;
 	    StgTRecChunk *tc = ((StgTRecChunk *) p);
 	    TRecEntry *e = &(tc -> entries[0]);
-	    gct->evac_step = 0;
+	    gct->evac_gen = 0;
 	    evacuate((StgClosure **)&tc->prev_chunk);
 	    for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
 	      evacuate((StgClosure **)&e->tvar);
 	      evacuate((StgClosure **)&e->expected_value);
 	      evacuate((StgClosure **)&e->new_value);
 	    }
-	    gct->evac_step = saved_evac_step;
+	    gct->evac_gen = saved_evac_gen;
 	    gct->failed_to_evac = rtsTrue; // mutable
 	    break;
 	  }
@@ -1011,11 +1017,11 @@ linear_scan:
 	case TREC_HEADER:
 	  {
 	    StgTRecHeader *trec = ((StgTRecHeader *) p);
-	    gct->evac_step = 0;
+	    gct->evac_gen = 0;
 	    evacuate((StgClosure **)&trec->enclosing_trec);
 	    evacuate((StgClosure **)&trec->current_chunk);
   	    evacuate((StgClosure **)&trec->invariants_to_check);
-	    gct->evac_step = saved_evac_step;
+	    gct->evac_gen = saved_evac_gen;
 	    gct->failed_to_evac = rtsTrue; // mutable
 	    break;
 	  }
@@ -1023,10 +1029,10 @@ linear_scan:
         case ATOMIC_INVARIANT:
           {
             StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-            gct->evac_step = 0;
+            gct->evac_gen = 0;
 	    evacuate(&invariant->code);
     	    evacuate((StgClosure **)&invariant->last_execution);
-	    gct->evac_step = saved_evac_step;
+	    gct->evac_gen = saved_evac_gen;
 	    gct->failed_to_evac = rtsTrue; // mutable
             break;
           }
@@ -1034,11 +1040,11 @@ linear_scan:
         case INVARIANT_CHECK_QUEUE:
           {
             StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-            gct->evac_step = 0;
+            gct->evac_gen = 0;
     	    evacuate((StgClosure **)&queue->invariant);
 	    evacuate((StgClosure **)&queue->my_execution);
             evacuate((StgClosure **)&queue->next_queue_entry);
-	    gct->evac_step = saved_evac_step;
+	    gct->evac_gen = saved_evac_gen;
 	    gct->failed_to_evac = rtsTrue; // mutable
             break;
           }
@@ -1050,53 +1056,11 @@ linear_scan:
 
 	if (gct->failed_to_evac) {
 	    gct->failed_to_evac = rtsFalse;
-	    if (gct->evac_step) {
-		recordMutableGen_GC((StgClosure *)q, gct->evac_step->gen);
+	    if (gct->evac_gen) {
+		recordMutableGen_GC((StgClosure *)q, gct->evac_gen->no);
 	    }
 	}
-	
-	// mark the next bit to indicate "scavenged"
-	mark(q+1, Bdescr(q));
-
-    } // while (!mark_stack_empty())
-
-    // start a new linear scan if the mark stack overflowed at some point
-    if (mark_stack_overflowed && oldgen_scan_bd == NULL) {
-	debugTrace(DEBUG_gc, "scavenge_mark_stack: starting linear scan");
-	mark_stack_overflowed = rtsFalse;
-	oldgen_scan_bd = oldest_gen->steps[0].old_blocks;
-	oldgen_scan = oldgen_scan_bd->start;
-    }
-
-    if (oldgen_scan_bd) {
-	// push a new thing on the mark stack
-    loop:
-	// find a closure that is marked but not scavenged, and start
-	// from there.
-	while (oldgen_scan < oldgen_scan_bd->free 
-	       && !is_marked(oldgen_scan,oldgen_scan_bd)) {
-	    oldgen_scan++;
-	}
-
-	if (oldgen_scan < oldgen_scan_bd->free) {
-
-	    // already scavenged?
-	    if (is_marked(oldgen_scan+1,oldgen_scan_bd)) {
-		oldgen_scan += sizeofW(StgHeader) + MIN_PAYLOAD_SIZE;
-		goto loop;
-	    }
-	    push_mark_stack(oldgen_scan);
-	    // ToDo: bump the linear scan by the actual size of the object
-	    oldgen_scan += sizeofW(StgHeader) + MIN_PAYLOAD_SIZE;
-	    goto linear_scan;
-	}
-
-	oldgen_scan_bd = oldgen_scan_bd->link;
-	if (oldgen_scan_bd != NULL) {
-	    oldgen_scan = oldgen_scan_bd->start;
-	    goto loop;
-	}
-    }
+    } // while (p = pop_mark_stack())
 }
 
 /* -----------------------------------------------------------------------------
@@ -1111,7 +1075,7 @@ static rtsBool
 scavenge_one(StgPtr p)
 {
     const StgInfoTable *info;
-    step *saved_evac_step = gct->evac_step;
+    generation *saved_evac_gen = gct->evac_gen;
     rtsBool no_luck;
     
     ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
@@ -1197,8 +1161,6 @@ scavenge_one(StgPtr p)
     }
 
     case CAF_BLACKHOLE:
-    case SE_CAF_BLACKHOLE:
-    case SE_BLACKHOLE:
     case BLACKHOLE:
 	break;
 	
@@ -1290,11 +1252,11 @@ scavenge_one(StgPtr p)
     case TVAR_WATCH_QUEUE:
       {
 	StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-	gct->evac_step = 0;
+	gct->evac_gen = 0;
         evacuate((StgClosure **)&wq->closure);
         evacuate((StgClosure **)&wq->next_queue_entry);
         evacuate((StgClosure **)&wq->prev_queue_entry);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	break;
       }
@@ -1302,10 +1264,10 @@ scavenge_one(StgPtr p)
     case TVAR:
       {
 	StgTVar *tvar = ((StgTVar *) p);
-	gct->evac_step = 0;
+	gct->evac_gen = 0;
 	evacuate((StgClosure **)&tvar->current_value);
         evacuate((StgClosure **)&tvar->first_watch_queue_entry);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	break;
       }
@@ -1313,11 +1275,11 @@ scavenge_one(StgPtr p)
     case TREC_HEADER:
       {
         StgTRecHeader *trec = ((StgTRecHeader *) p);
-        gct->evac_step = 0;
+        gct->evac_gen = 0;
 	evacuate((StgClosure **)&trec->enclosing_trec);
 	evacuate((StgClosure **)&trec->current_chunk);
         evacuate((StgClosure **)&trec->invariants_to_check);
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
         break;
       }
@@ -1327,14 +1289,14 @@ scavenge_one(StgPtr p)
 	StgWord i;
 	StgTRecChunk *tc = ((StgTRecChunk *) p);
 	TRecEntry *e = &(tc -> entries[0]);
-	gct->evac_step = 0;
+	gct->evac_gen = 0;
 	evacuate((StgClosure **)&tc->prev_chunk);
 	for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
 	  evacuate((StgClosure **)&e->tvar);
 	  evacuate((StgClosure **)&e->expected_value);
 	  evacuate((StgClosure **)&e->new_value);
 	}
-	gct->evac_step = saved_evac_step;
+	gct->evac_gen = saved_evac_gen;
 	gct->failed_to_evac = rtsTrue; // mutable
 	break;
       }
@@ -1342,10 +1304,10 @@ scavenge_one(StgPtr p)
     case ATOMIC_INVARIANT:
     {
       StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-      gct->evac_step = 0;
+      gct->evac_gen = 0;
       evacuate(&invariant->code);
       evacuate((StgClosure **)&invariant->last_execution);
-      gct->evac_step = saved_evac_step;
+      gct->evac_gen = saved_evac_gen;
       gct->failed_to_evac = rtsTrue; // mutable
       break;
     }
@@ -1353,32 +1315,23 @@ scavenge_one(StgPtr p)
     case INVARIANT_CHECK_QUEUE:
     {
       StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-      gct->evac_step = 0;
+      gct->evac_gen = 0;
       evacuate((StgClosure **)&queue->invariant);
       evacuate((StgClosure **)&queue->my_execution);
       evacuate((StgClosure **)&queue->next_queue_entry);
-      gct->evac_step = saved_evac_step;
+      gct->evac_gen = saved_evac_gen;
       gct->failed_to_evac = rtsTrue; // mutable
       break;
     }
 
+    case IND:
+        // IND can happen, for example, when the interpreter allocates
+        // a gigantic AP closure (more than one block), which ends up
+        // on the large-object list and then gets updated.  See #3424.
     case IND_OLDGEN:
     case IND_OLDGEN_PERM:
     case IND_STATIC:
-    {
-	/* Careful here: a THUNK can be on the mutable list because
-	 * it contains pointers to young gen objects.  If such a thunk
-	 * is updated, the IND_OLDGEN will be added to the mutable
-	 * list again, and we'll scavenge it twice.  evacuate()
-	 * doesn't check whether the object has already been
-	 * evacuated, so we perform that check here.
-	 */
-	StgClosure *q = ((StgInd *)p)->indirectee;
-	if (HEAP_ALLOCED(q) && Bdescr((StgPtr)q)->flags & BF_EVACUATED) {
-	    break;
-	}
 	evacuate(&((StgInd *)p)->indirectee);
-    }
 
 #if 0 && defined(DEBUG)
       if (RtsFlags.DebugFlags.gc) 
@@ -1386,21 +1339,21 @@ scavenge_one(StgPtr p)
        * promoted 
        */
       { 
-	StgPtr start = gen->steps[0].scan;
-	bdescr *start_bd = gen->steps[0].scan_bd;
+	StgPtr start = gen->scan;
+	bdescr *start_bd = gen->scan_bd;
 	nat size = 0;
-	scavenge(&gen->steps[0]);
-	if (start_bd != gen->steps[0].scan_bd) {
+	scavenge(&gen);
+	if (start_bd != gen->scan_bd) {
 	  size += (P_)BLOCK_ROUND_UP(start) - start;
 	  start_bd = start_bd->link;
-	  while (start_bd != gen->steps[0].scan_bd) {
+	  while (start_bd != gen->scan_bd) {
 	    size += BLOCK_SIZE_W;
 	    start_bd = start_bd->link;
 	  }
-	  size += gen->steps[0].scan -
-	    (P_)BLOCK_ROUND_DOWN(gen->steps[0].scan);
+	  size += gen->scan -
+	    (P_)BLOCK_ROUND_DOWN(gen->scan);
 	} else {
-	  size = gen->steps[0].scan - start;
+	  size = gen->scan - start;
 	}
 	debugBelch("evac IND_OLDGEN: %ld bytes", size * sizeof(W_));
       }
@@ -1425,14 +1378,11 @@ scavenge_one(StgPtr p)
    -------------------------------------------------------------------------- */
 
 void
-scavenge_mutable_list(generation *gen)
+scavenge_mutable_list(bdescr *bd, generation *gen)
 {
-    bdescr *bd;
     StgPtr p, q;
 
-    bd = gen->saved_mut_list;
-
-    gct->evac_step = &gen->steps[0];
+    gct->evac_gen = gen;
     for (; bd != NULL; bd = bd->link) {
 	for (q = bd->start; q < bd->free; q++) {
 	    p = (StgPtr)*q;
@@ -1462,23 +1412,23 @@ scavenge_mutable_list(generation *gen)
 	    // definitely doesn't point into a young generation.
 	    // Clean objects don't need to be scavenged.  Some clean
 	    // objects (MUT_VAR_CLEAN) are not kept on the mutable
-	    // list at all; others, such as MUT_ARR_PTRS_CLEAN and
-	    // TSO, are always on the mutable list.
+	    // list at all; others, such as MUT_ARR_PTRS_CLEAN
+	    // are always on the mutable list.
 	    //
 	    switch (get_itbl((StgClosure *)p)->type) {
 	    case MUT_ARR_PTRS_CLEAN:
-		recordMutableGen_GC((StgClosure *)p,gen);
+		recordMutableGen_GC((StgClosure *)p,gen->no);
 		continue;
 	    case TSO: {
 		StgTSO *tso = (StgTSO *)p;
-		if ((tso->flags & TSO_DIRTY) == 0) {
+		if (tso->dirty == 0) {
                     // Must be on the mutable list because its link
                     // field is dirty.
                     ASSERT(tso->flags & TSO_LINK_DIRTY);
 
                     scavenge_TSO_link(tso);
                     if (gct->failed_to_evac) {
-                        recordMutableGen_GC((StgClosure *)p,gen);
+                        recordMutableGen_GC((StgClosure *)p,gen->no);
                         gct->failed_to_evac = rtsFalse;
                     } else {
                         tso->flags &= ~TSO_LINK_DIRTY;
@@ -1493,14 +1443,28 @@ scavenge_mutable_list(generation *gen)
 	    if (scavenge_one(p)) {
 		// didn't manage to promote everything, so put the
 		// object back on the list.
-		recordMutableGen_GC((StgClosure *)p,gen);
+		recordMutableGen_GC((StgClosure *)p,gen->no);
 	    }
 	}
     }
+}
 
-    // free the old mut_list
-    freeChain_sync(gen->saved_mut_list);
-    gen->saved_mut_list = NULL;
+void
+scavenge_capability_mut_lists (Capability *cap)
+{
+    nat g;
+
+    /* Mutable lists from each generation > N
+     * we want to *scavenge* these roots, not evacuate them: they're not
+     * going to move in this GC.
+     * Also do them in reverse generation order, for the usual reason:
+     * namely to reduce the likelihood of spurious old->new pointers.
+     */
+    for (g = RtsFlags.GcFlags.generations-1; g > N; g--) {
+        scavenge_mutable_list(cap->saved_mut_lists[g], &generations[g]);
+        freeChain_sync(cap->saved_mut_lists[g]);
+        cap->saved_mut_lists[g] = NULL;
+    }
 }
 
 /* -----------------------------------------------------------------------------
@@ -1521,7 +1485,7 @@ scavenge_static(void)
 
   /* Always evacuate straight to the oldest generation for static
    * objects */
-  gct->evac_step = &oldest_gen->steps[0];
+  gct->evac_gen = oldest_gen;
 
   /* keep going until we've scavenged all the objects on the linked
      list... */
@@ -1566,7 +1530,7 @@ scavenge_static(void)
 	 */
 	if (gct->failed_to_evac) {
 	  gct->failed_to_evac = rtsFalse;
-	  recordMutableGen_GC((StgClosure *)p,oldest_gen);
+	  recordMutableGen_GC((StgClosure *)p,oldest_gen->no);
 	}
 	break;
       }
@@ -1686,24 +1650,34 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
 	// the indirection into an IND_PERM, so that evacuate will
 	// copy the indirection into the old generation instead of
 	// discarding it.
+        //
+        // Note [upd-black-hole]
+        // One slight hiccup is that the THUNK_SELECTOR machinery can
+        // overwrite the updatee with an IND.  In parallel GC, this
+        // could even be happening concurrently, so we can't check for
+        // the IND.  Fortunately if we assume that blackholing is
+        // happening (either lazy or eager), then we can be sure that
+        // the updatee is never a THUNK_SELECTOR and we're ok.
+        // NB. this is a new invariant: blackholing is not optional.
     {
         nat type;
         const StgInfoTable *i;
+        StgClosure *updatee;
 
-        i = ((StgUpdateFrame *)p)->updatee->header.info;
+        updatee = ((StgUpdateFrame *)p)->updatee;
+        i = updatee->header.info;
         if (!IS_FORWARDING_PTR(i)) {
-            type = get_itbl(((StgUpdateFrame *)p)->updatee)->type;
+            type = get_itbl(updatee)->type;
             if (type == IND) {
-                ((StgUpdateFrame *)p)->updatee->header.info = 
-                    (StgInfoTable *)&stg_IND_PERM_info;
+                updatee->header.info = &stg_IND_PERM_info;
             } else if (type == IND_OLDGEN) {
-                ((StgUpdateFrame *)p)->updatee->header.info = 
-                    (StgInfoTable *)&stg_IND_OLDGEN_PERM_info;
+                updatee->header.info = &stg_IND_OLDGEN_PERM_info;
             }            
-            evacuate(&((StgUpdateFrame *)p)->updatee);
-            p += sizeofW(StgUpdateFrame);
-            continue;
         }
+        evacuate(&((StgUpdateFrame *)p)->updatee);
+        ASSERT(GET_CLOSURE_TAG(((StgUpdateFrame *)p)->updatee) == 0);
+        p += sizeofW(StgUpdateFrame);
+        continue;
     }
 
       // small bitmap (< 32 entries, or 64 on a 64-bit machine) 
@@ -1798,19 +1772,19 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
 /*-----------------------------------------------------------------------------
   scavenge the large object list.
 
-  evac_step set by caller; similar games played with evac_step as with
+  evac_gen set by caller; similar games played with evac_gen as with
   scavenge() - see comment at the top of scavenge().  Most large
-  objects are (repeatedly) mutable, so most of the time evac_step will
+  objects are (repeatedly) mutable, so most of the time evac_gen will
   be zero.
   --------------------------------------------------------------------------- */
 
 static void
-scavenge_large (step_workspace *ws)
+scavenge_large (gen_workspace *ws)
 {
     bdescr *bd;
     StgPtr p;
 
-    gct->evac_step = ws->step;
+    gct->evac_gen = ws->gen;
 
     bd = ws->todo_large_objects;
     
@@ -1822,15 +1796,15 @@ scavenge_large (step_workspace *ws)
 	// the front when evacuating.
 	ws->todo_large_objects = bd->link;
 	
-	ACQUIRE_SPIN_LOCK(&ws->step->sync_large_objects);
-	dbl_link_onto(bd, &ws->step->scavenged_large_objects);
-	ws->step->n_scavenged_large_blocks += bd->blocks;
-	RELEASE_SPIN_LOCK(&ws->step->sync_large_objects);
+	ACQUIRE_SPIN_LOCK(&ws->gen->sync_large_objects);
+	dbl_link_onto(bd, &ws->gen->scavenged_large_objects);
+	ws->gen->n_scavenged_large_blocks += bd->blocks;
+	RELEASE_SPIN_LOCK(&ws->gen->sync_large_objects);
 	
 	p = bd->start;
 	if (scavenge_one(p)) {
-	    if (ws->step->gen_no > 0) {
-		recordMutableGen_GC((StgClosure *)p, ws->step->gen);
+	    if (ws->gen->no > 0) {
+		recordMutableGen_GC((StgClosure *)p, ws->gen->no);
 	    }
 	}
 
@@ -1842,7 +1816,7 @@ scavenge_large (step_workspace *ws)
 /* ----------------------------------------------------------------------------
    Look for work to do.
 
-   We look for the oldest step that has either a todo block that can
+   We look for the oldest gen that has either a todo block that can
    be scanned, or a block of work on the global queue that we can
    scan.
 
@@ -1861,8 +1835,8 @@ scavenge_large (step_workspace *ws)
 static rtsBool
 scavenge_find_work (void)
 {
-    int s;
-    step_workspace *ws;
+    int g;
+    gen_workspace *ws;
     rtsBool did_something, did_anything;
     bdescr *bd;
 
@@ -1872,11 +1846,8 @@ scavenge_find_work (void)
 
 loop:
     did_something = rtsFalse;
-    for (s = total_steps-1; s >= 0; s--) {
-        if (s == 0 && RtsFlags.GcFlags.generations > 1) { 
-            continue; 
-        }
-        ws = &gct->steps[s];
+    for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
+        ws = &gct->gens[g];
         
         gct->scan_bd = NULL;
 
@@ -1896,7 +1867,7 @@ loop:
             break;
         }
 
-        if ((bd = grab_todo_block(ws)) != NULL) {
+        if ((bd = grab_local_todo_block(ws)) != NULL) {
             scavenge_block(bd);
             did_something = rtsTrue;
             break;
@@ -1907,6 +1878,25 @@ loop:
         did_anything = rtsTrue;
         goto loop;
     }
+
+#if defined(THREADED_RTS)
+    if (work_stealing) {
+        // look for work to steal
+        for (g = RtsFlags.GcFlags.generations-1; g >= 0; g--) {
+            if ((bd = steal_todo_block(g)) != NULL) {
+                scavenge_block(bd);
+                did_something = rtsTrue;
+                break;
+            }
+        }
+
+        if (did_something) {
+            did_anything = rtsTrue;
+            goto loop;
+        }
+    }
+#endif
+
     // only return when there is no more work to do
 
     return did_anything;
@@ -1931,8 +1921,7 @@ loop:
     }
     
     // scavenge objects in compacted generation
-    if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
-	(mark_stack_bdescr != NULL && !mark_stack_empty())) {
+    if (mark_stack_bd != NULL && !mark_stack_empty()) {
 	scavenge_mark_stack();
 	work_to_do = rtsTrue;
     }