Unify src/common/'s definitions of MaxAllocSize.

As threatened in the previous patch, define MaxAllocSize in
src/include/common/fe_memutils.h rather than having several
copies of it in different src/common/*.c files.  This also
provides an opportunity to document it better.

While this would probably be safe to back-patch, I'll refrain
(for now anyway).

1 files changed, 12 insertions, 0 deletions

diff --git a/src/include/common/fe_memutils.h b/src/include/common/fe_memutils.h
index 492cc97e8d1..6544ebb44e5 100644
--- a/src/include/common/fe_memutils.h
+++ b/src/include/common/fe_memutils.h
@@ -10,6 +10,18 @@
 #define FE_MEMUTILS_H
 
 /*
+ * Assumed maximum size for allocation requests.
+ *
+ * We don't enforce this, so the actual maximum is the platform's SIZE_MAX.
+ * But it's useful to have it defined in frontend builds, so that common
+ * code can check for oversized requests without having frontend-vs-backend
+ * differences.  Also, some code relies on MaxAllocSize being no more than
+ * INT_MAX/2, so rather than setting this to SIZE_MAX, make it the same as
+ * the backend's value.
+ */
+#define MaxAllocSize	((Size) 0x3fffffff) /* 1 gigabyte - 1 */
+
+/*
  * Flags for pg_malloc_extended and palloc_extended, deliberately named
  * the same as the backend flags.
  */