[commit: ghc] wip/nonmoving-gc: rts: Introduce non-moving heap census (8cdc755)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/nonmoving-gc
Link       : http://ghc.haskell.org/trac/ghc/changeset/8cdc755bd3af14f4080e6dbbf35f6e8859c7a834/ghc

>---------------------------------------------------------------

commit 8cdc755bd3af14f4080e6dbbf35f6e8859c7a834
Author: Ben Gamari <ben at well-typed.com>
Date:   Tue Feb 5 11:52:13 2019 -0500

    rts: Introduce non-moving heap census
    
    This introduces a simple census of the non-moving heap (not to be
    confused with the heap census used by the heap profiler). This
    collects basic heap usage information (number of allocated and free
    blocks) which is useful when characterising fragmentation of the
    nonmoving heap.


>---------------------------------------------------------------

8cdc755bd3af14f4080e6dbbf35f6e8859c7a834
 rts/sm/NonMoving.c                        |  5 ++
 rts/sm/NonMovingCensus.c                  | 94 +++++++++++++++++++++++++++++++
 rts/{posix/TTY.h => sm/NonMovingCensus.h} |  6 +-
 3 files changed, 102 insertions(+), 3 deletions(-)

diff --git a/rts/sm/NonMoving.c b/rts/sm/NonMoving.c
index ede1fe2..2e767e2 100644
--- a/rts/sm/NonMoving.c
+++ b/rts/sm/NonMoving.c
@@ -21,6 +21,7 @@
 #include "NonMoving.h"
 #include "NonMovingMark.h"
 #include "NonMovingSweep.h"
+#include "NonMovingCensus.h"
 #include "StablePtr.h" // markStablePtrTable
 #include "Schedule.h" // markScheduler
 #include "Weak.h" // dead_weak_ptr_list
@@ -684,6 +685,10 @@ static void nonmovingMark_(MarkQueue *mark_queue, StgWeak **dead_weaks, StgTSO *
     ASSERT(nonmovingHeap.sweep_list == NULL);
     debugTrace(DEBUG_nonmoving_gc, "Finished sweeping.");
     traceConcSweepEnd();
+#if defined(DEBUG)
+    if (RtsFlags.DebugFlags.nonmoving_gc)
+        nonmovingPrintAllocatorCensus();
+#endif
 
     // TODO: Remainder of things done by GarbageCollect (update stats)
 
diff --git a/rts/sm/NonMovingCensus.c b/rts/sm/NonMovingCensus.c
new file mode 100644
index 0000000..349ac77
--- /dev/null
+++ b/rts/sm/NonMovingCensus.c
@@ -0,0 +1,94 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 1998-2018
+ *
+ * Non-moving garbage collector and allocator: Accounting census
+ *
+ * This is a simple space accounting census useful for characterising
+ * fragmentation in the nonmoving heap.
+ *
+ * ---------------------------------------------------------------------------*/
+
+#include "Rts.h"
+#include "NonMoving.h"
+#include "Trace.h"
+#include "NonMovingCensus.h"
+
+struct NonmovingAllocCensus {
+    uint32_t n_active_segs;
+    uint32_t n_filled_segs;
+    uint32_t n_live_blocks;
+    uint32_t n_live_words;
+};
+
+// N.B. This may miss segments in the event of concurrent mutation (e.g. if a
+// mutator retires its current segment to the filled list).
+static struct NonmovingAllocCensus
+nonmovingAllocatorCensus(struct NonmovingAllocator *alloc)
+{
+    struct NonmovingAllocCensus census = {0, 0, 0, 0};
+
+    for (struct NonmovingSegment *seg = alloc->filled;
+         seg != NULL;
+         seg = seg->link)
+    {
+        census.n_filled_segs++;
+        census.n_live_blocks += nonmovingSegmentBlockCount(seg);
+        unsigned int n = nonmovingSegmentBlockCount(seg);
+        for (unsigned int i=0; i < n; i++) {
+            StgClosure *c = (StgClosure *) nonmovingSegmentGetBlock(seg, i);
+            census.n_live_words += closure_sizeW(c);
+        }
+    }
+
+    for (struct NonmovingSegment *seg = alloc->active;
+         seg != NULL;
+         seg = seg->link)
+    {
+        census.n_active_segs++;
+        unsigned int n = nonmovingSegmentBlockCount(seg);
+        for (unsigned int i=0; i < n; i++) {
+            if (nonmovingGetMark(seg, i)) {
+                StgClosure *c = (StgClosure *) nonmovingSegmentGetBlock(seg, i);
+                census.n_live_words += closure_sizeW(c);
+                census.n_live_blocks++;
+            }
+        }
+    }
+
+    for (unsigned int cap=0; cap < n_capabilities; cap++)
+    {
+        struct NonmovingSegment *seg = alloc->current[cap];
+        unsigned int n = nonmovingSegmentBlockCount(seg);
+        for (unsigned int i=0; i < n; i++) {
+            if (nonmovingGetMark(seg, i)) {
+                StgClosure *c = (StgClosure *) nonmovingSegmentGetBlock(seg, i);
+                census.n_live_words += closure_sizeW(c);
+                census.n_live_blocks++;
+            }
+        }
+    }
+    return census;
+}
+
+void nonmovingPrintAllocatorCensus()
+{
+    for (int i=0; i < NONMOVING_ALLOCA_CNT; i++) {
+        struct NonmovingAllocCensus census =
+            nonmovingAllocatorCensus(nonmovingHeap.allocators[i]);
+
+        uint32_t blk_size = 1 << (i + NONMOVING_ALLOCA0);
+        // We define occupancy as the fraction of space that is used for useful
+        // data (that is, live and not slop).
+        double occupancy = 100.0 * census.n_live_words * sizeof(W_)
+            / (census.n_live_blocks * blk_size);
+        if (census.n_live_blocks == 0) occupancy = 100;
+        (void) occupancy; // silence warning if !DEBUG
+        debugTrace(DEBUG_nonmoving_gc, "Allocator %d (%d bytes - %d bytes): "
+                   "%d active segs, %d filled segs, %d live blocks, %d live words "
+                   "(%2.1f%% occupancy)",
+                   i, 1 << (i + NONMOVING_ALLOCA0 - 1), 1 << (i + NONMOVING_ALLOCA0),
+                   census.n_active_segs, census.n_filled_segs, census.n_live_blocks, census.n_live_words,
+                   occupancy);
+    }
+}
diff --git a/rts/posix/TTY.h b/rts/sm/NonMovingCensus.h
similarity index 57%
copy from rts/posix/TTY.h
copy to rts/sm/NonMovingCensus.h
index eb1863c..a4f84c4 100644
--- a/rts/posix/TTY.h
+++ b/rts/sm/NonMovingCensus.h
@@ -1,11 +1,11 @@
 /* -----------------------------------------------------------------------------
  *
- * (c) The GHC Team, 1998-2009
+ * (c) The GHC Team, 1998-2018
  *
- * TTY-related functionality
+ * Non-moving garbage collector and allocator: Accounting census
  *
  * ---------------------------------------------------------------------------*/
 
 #pragma once
 
-RTS_PRIVATE void resetTerminalSettings (void);
+void nonmovingPrintAllocatorCensus(void);