Fix potential VM map fragmentation regression.

Revert 245ae60 (Support --with-lg-page
values larger than actual page size.), because it could cause VM map
fragmentation if the kernel grows mmap()ed memory downward.

This resolves jemalloc#391.

Author: jasone

include/jemalloc/internal/jemalloc_internal.h.in

@@ -754,7 +754,7 @@ sa2u(size_t size, size_t alignment)
 		 * Calculate the size of the over-size run that arena_palloc()
 		 * would need to allocate in order to guarantee the alignment.
 		 */
-		if (usize + large_pad + alignment <= arena_maxrun)
+		if (usize + large_pad + alignment - PAGE <= arena_maxrun)
 			return (usize);
 	}
 
@@ -784,7 +784,7 @@ sa2u(size_t size, size_t alignment)
 	 * Calculate the multi-chunk mapping that huge_palloc() would need in
 	 * order to guarantee the alignment.
 	 */
-	if (usize + alignment < usize) {
+	if (usize + alignment - PAGE < usize) {
 		/* size_t overflow. */
 		return (0);
 	}

src/arena.c

@@ -2687,7 +2687,7 @@ arena_palloc_large(tsdn_t *tsdn, arena_t *arena, size_t usize, size_t alignment,
 		return (NULL);
 
 	alignment = PAGE_CEILING(alignment);
-	alloc_size = usize + large_pad + alignment;
+	alloc_size = usize + large_pad + alignment - PAGE;
 
 	malloc_mutex_lock(tsdn, &arena->lock);
 	run = arena_run_alloc_large(tsdn, arena, alloc_size, false);

src/chunk_mmap.c

@@ -9,7 +9,7 @@ chunk_alloc_mmap_slow(size_t size, size_t alignment, bool *zero, bool *commit)
 	void *ret;
 	size_t alloc_size;
 
-	alloc_size = size + alignment;
+	alloc_size = size + alignment - PAGE;
 	/* Beware size_t wrap-around. */
 	if (alloc_size < size)
 		return (NULL);