Remove extra GC stat fields and rename remaining

Before making stats struct and thus standardizing it, field set
it defines has to be reduced to minimal amount meaningful to
any GC implementation.

src/gc/impl/conservative/gc.d

@@ -1157,8 +1157,8 @@ class ConservativeGC : GC
             GCStats stats;
 
             getStats(stats);
-            debug(PRINTF) printf("poolsize = %zx, usedsize = %zx, freelistsize = %zx\n",
-                    stats.poolsize, stats.usedsize, stats.freelistsize);
+            debug(PRINTF) printf("heapSize = %zx, freeSize = %zx\n",
+                stats.heapSize, stats.freeSize);
         }
 
         gcx.log_collect();
@@ -1223,11 +1223,7 @@ class ConservativeGC : GC
             for (size_t j = 0; j < pool.npages; j++)
             {
                 Bins bin = cast(Bins)pool.pagetable[j];
-                if (bin == B_FREE)
-                    stats.freeblocks++;
-                else if (bin == B_PAGE)
-                    stats.pageblocks++;
-                else if (bin < B_PAGE)
+                if (bin < B_PAGE)
                     bsize += PAGESIZE;
             }
         }
@@ -1244,9 +1240,8 @@ class ConservativeGC : GC
 
         usize = bsize - flsize;
 
-        stats.poolsize = psize;
-        stats.usedsize = bsize - flsize;
-        stats.freelistsize = flsize;
+        stats.usedSize = bsize - flsize;
+        stats.freeSize = flsize;
     }
 }
 

src/gc/stats.d

@@ -13,15 +13,13 @@
  */
 module gc.stats;
 
-
 /**
- *
+ * Aggregation of GC stats to be exposed via public API
  */
 struct GCStats
 {
-    size_t poolsize;        // total size of pool
-    size_t usedsize;        // bytes allocated
-    size_t freeblocks;      // number of blocks marked FREE
-    size_t freelistsize;    // total of memory on free lists
-    size_t pageblocks;      // number of blocks marked PAGE
+    /// total size of GC heap
+    size_t usedSize;
+    /// free bytes on the GC heap (might only get updated after a collection)
+    size_t freeSize;
 }