Add a batch allocation interface to the PAI.

For now, no real allocator actually implements this interface; this will change
in subsequent diffs.

include/jemalloc/internal/pai.h

@@ -8,6 +8,14 @@ struct pai_s {
 	/* Returns NULL on failure. */
 	edata_t *(*alloc)(tsdn_t *tsdn, pai_t *self, size_t size,
 	    size_t alignment, bool zero);
+	/*
+	 * Returns the number of extents added to the list (which may be fewer
+	 * than requested, in case of OOM).  The list should already be
+	 * initialized.  The only alignment guarantee is page-alignment, and
+	 * the results are not necessarily zeroed.
+	 */
+	size_t (*alloc_batch)(tsdn_t *tsdn, pai_t *self, size_t size,
+	    size_t nallocs, edata_list_active_t *results);
 	bool (*expand)(tsdn_t *tsdn, pai_t *self, edata_t *edata,
 	    size_t old_size, size_t new_size, bool zero);
 	bool (*shrink)(tsdn_t *tsdn, pai_t *self, edata_t *edata,
@@ -28,6 +36,12 @@ pai_alloc(tsdn_t *tsdn, pai_t *self, size_t size, size_t alignment, bool zero) {
 	return self->alloc(tsdn, self, size, alignment, zero);
 }
 
+static inline size_t
+pai_alloc_batch(tsdn_t *tsdn, pai_t *self, size_t size, size_t nallocs,
+    edata_list_active_t *results) {
+	return self->alloc_batch(tsdn, self, size, nallocs, results);
+}
+
 static inline bool
 pai_expand(tsdn_t *tsdn, pai_t *self, edata_t *edata, size_t old_size,
     size_t new_size, bool zero) {
@@ -51,9 +65,12 @@ pai_dalloc_batch(tsdn_t *tsdn, pai_t *self, edata_list_active_t *list) {
 }
 
 /*
- * An implementation of batch deallocation that simply calls dalloc once for
+ * An implementation of batch allocation that simply calls alloc once for
  * each item in the list.
  */
+size_t pai_alloc_batch_default(tsdn_t *tsdn, pai_t *self, size_t size,
+    size_t nallocs, edata_list_active_t *results);
+/* Ditto, for dalloc. */
 void pai_dalloc_batch_default(tsdn_t *tsdn, pai_t *self,
     edata_list_active_t *list);