Add hpa_central module

This will be the centralized component of the coming hugepage allocator; the
source of larger chunks of memory from which smaller ones can be obtained.

include/jemalloc/internal/hpa_central.h

@@ -0,0 +1,47 @@
+#ifndef JEMALLOC_INTERNAL_HPA_CENTRAL_H
+#define JEMALLOC_INTERNAL_HPA_CENTRAL_H
+
+#include "jemalloc/internal/base.h"
+#include "jemalloc/internal/emap.h"
+
+typedef struct hpa_central_s hpa_central_t;
+struct hpa_central_s {
+	/* The emap we use for metadata operations. */
+	emap_t *emap;
+
+	edata_cache_t *edata_cache;
+	eset_t eset;
+
+	size_t sn_next;
+};
+
+void hpa_central_init(hpa_central_t *central, edata_cache_t *edata_cache,
+    emap_t *emap);
+/*
+ * Tries to satisfy the given allocation request with an extent already given to
+ * central.
+ */
+edata_t *hpa_central_alloc_reuse(tsdn_t *tsdn, hpa_central_t *central,
+    size_t size_min, size_t size_goal);
+/*
+ * Adds the given edata to the central allocator as a new allocation.  The
+ * intent is that after a reuse attempt fails, the caller can allocate a new
+ * extent using whatever growth policy it prefers and allocate from that, giving
+ * the excess to the hpa_central_t (this is analogous to the
+ * extent_grow_retained functionality; we can allocate address space in
+ * exponentially growing chunks).
+ *
+ * The edata_t should come from the same base that this hpa was initialized
+ * with.  Only complete extents should be added (i.e. those for which the head
+ * bit is true, and for which their successor is either not owned by jemalloc
+ * or also has a head bit of true).  It should be active, large enough to
+ * satisfy the requested allocation, and not already in the emap.
+ *
+ * If this returns true, then we did not accept the extent, and took no action.
+ * Otherwise, modifies *edata to satisfy the allocation.
+ */
+bool hpa_central_alloc_grow(tsdn_t *tsdn, hpa_central_t *central,
+    size_t size, edata_t *to_add);
+void hpa_central_dalloc(tsdn_t *tsdn, hpa_central_t *central, edata_t *edata);
+
+#endif /* JEMALLOC_INTERNAL_HPA_CENTRAL_H */