Support --with-lg-page values larger than actual page size.

During over-allocation in preparation for creating aligned mappings,
allocate one more page than necessary if PAGE is the actual page size,
so that trimming still succeeds even if the system returns a mapping
that has less than PAGE alignment.  This allows compiling with e.g. 64
KiB "pages" on systems that actually use 4 KiB pages.

Note that for e.g. --with-lg-page=21, it is also necessary to increase
the chunk size (e.g. --with-malloc-conf=lg_chunk:22) so that there are
at least two "pages" per chunk.  In practice this isn't a particularly
compelling configuration because so much (unusable) virtual memory is
dedicated to chunk headers.

include/jemalloc/internal/bitmap.h

@@ -17,8 +17,8 @@ typedef unsigned long bitmap_t;
 
 /*
  * Do some analysis on how big the bitmap is before we use a tree.  For a brute
- * force linear search, if we would have to call ffsl more than 2^3 times, use a
- * tree instead.
+ * force linear search, if we would have to call ffs_lu() more than 2^3 times,
+ * use a tree instead.
  */
 #if LG_BITMAP_MAXBITS - LG_BITMAP_GROUP_NBITS > 3
 #  define USE_TREE

include/jemalloc/internal/jemalloc_internal.h.in

@@ -741,7 +741,7 @@ 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 - PAGE <= arena_maxrun)
+		if (usize + large_pad + alignment <= arena_maxrun)
 			return (usize);
 	}
 
@@ -771,7 +771,7 @@ 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 - PAGE < usize) {
+	if (usize + alignment < usize) {
 		/* size_t overflow. */
 		return (0);
 	}

src/arena.c

@@ -2500,7 +2500,7 @@ arena_palloc_large(tsd_t *tsd, arena_t *arena, size_t usize, size_t alignment,
 		return (NULL);
 
 	alignment = PAGE_CEILING(alignment);
-	alloc_size = usize + large_pad + alignment - PAGE;
+	alloc_size = usize + large_pad + alignment;
 
 	malloc_mutex_lock(&arena->lock);
 	run = arena_run_alloc_large(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 - PAGE;
+	alloc_size = size + alignment;
 	/* Beware size_t wrap-around. */
 	if (alloc_size < size)
 		return (NULL);