Permallocate scheduler cells in chunks

Scheduler cells are small objects that come and go in great quantities.
Even though they are allocated and deallocated a lot, they tend to a
steady state quantity, so put together a heap that is unique for each
cell type.

This heap actually saves memory overall because cells are allocated in
chunks, thus eliminating allocator overhead, and they are pulled/pushed
from/to a heap very quickly so that what overhead remains is slight and
bounded.

vvp/slab.h

@@ -0,0 +1,80 @@
+#ifndef __slab_H
+#define __slab_H
+/*
+ * Copyright (c) 2008 Picture Elements, Inc.
+ *    Stephen Williams ([email protected])
+ *
+ *    This source code is free software; you can redistribute it
+ *    and/or modify it in source code form under the terms of the GNU
+ *    General Public License as published by the Free Software
+ *    Foundation; either version 2 of the License, or (at your option)
+ *    any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program; if not, write to the Free Software
+ *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+
+template <size_t SLAB_SIZE, size_t CHUNK_COUNT> class slab_t {
+
+      union item_cell_u {
+	    item_cell_u*next;
+	    char space[SLAB_SIZE];
+      };
+
+    public:
+      slab_t();
+
+      void* alloc_slab();
+      void  free_slab(void*);
+
+      unsigned long pool;
+
+    private:
+      item_cell_u*heap_;
+      item_cell_u initial_chunk_[CHUNK_COUNT];
+};
+
+template <size_t SLAB_SIZE, size_t CHUNK_COUNT>
+slab_t<SLAB_SIZE,CHUNK_COUNT>::slab_t()
+{
+      pool = CHUNK_COUNT;
+      heap_ = initial_chunk_;
+      for (unsigned idx = 0 ; idx < CHUNK_COUNT-1 ; idx += 1)
+	    initial_chunk_[idx].next = initial_chunk_+idx+1;
+
+      initial_chunk_[CHUNK_COUNT-1].next = 0;
+}
+
+template <size_t SLAB_SIZE, size_t CHUNK_COUNT>
+inline void* slab_t<SLAB_SIZE,CHUNK_COUNT>::alloc_slab()
+{
+      if (heap_ == 0) {
+	    item_cell_u*chunk = new item_cell_u[CHUNK_COUNT];
+	    for (unsigned idx = 0 ; idx < CHUNK_COUNT ; idx += 1) {
+		  chunk[idx].next = heap_;
+		  heap_ = chunk+idx;
+	    }
+	    pool += CHUNK_COUNT;
+      }
+
+      item_cell_u*cur = heap_;
+      heap_ = heap_->next;
+      return cur;
+}
+
+template <size_t SLAB_SIZE, size_t CHUNK_COUNT>
+inline void slab_t<SLAB_SIZE,CHUNK_COUNT>::free_slab(void*ptr)
+{
+      item_cell_u*cur = reinterpret_cast<item_cell_u*> (ptr);
+      cur->next = heap_;
+      heap_ = cur;
+}
+
+#endif