selftests/mm: change MAP_CHUNK_SIZE

Patch series "selftests: Fix virtual address range for arm64", v2.

When the virtual address range selftest is run on arm64 and x86 platforms,
it is observed that both the low and high VA range iterations are skipped
when the MAP_CHUNK_SIZE is set to 16GB.  The MAP_CHUNK_SIZE is changed to
1GB to resolve this issue, following which support for arm64 platform is
added by changing the NR_CHUNKS_HIGH for aarch64 to accommodate up to 4PB
of virtual address space allocation requests.  Dynamic memory allocation
of array holding addresses is introduced to prevent overflow of the stack.
Finally, the overcommit_policy is set as OVERCOMMIT_ALWAYS to prevent the
kernel from denying a memory allocation request based on a platform's
physical memory availability.


This patch (of 3):

mmap() fails to allocate 16GB virtual space chunk, skipping both low and
high VA range iterations.  Hence, reduce MAP_CHUNK_SIZE to 1GB and update
relevant macros as required.

Link: https://lkml.kernel.org/r/20230323060121.1175830-1-chaitanyas.prakash@arm.com
Link: https://lkml.kernel.org/r/20230323060121.1175830-2-chaitanyas.prakash@arm.comSigned-off-by: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/virtual_address_range.c

@@ -15,11 +15,15 @@
 
 /*
  * Maximum address range mapped with a single mmap()
- * call is little bit more than 16GB. Hence 16GB is
+ * call is little bit more than 1GB. Hence 1GB is
  * chosen as the single chunk size for address space
  * mapping.
  */
-#define MAP_CHUNK_SIZE   17179869184UL /* 16GB */
+
+#define SZ_1GB	(1024 * 1024 * 1024UL)
+#define SZ_1TB	(1024 * 1024 * 1024 * 1024UL)
+
+#define MAP_CHUNK_SIZE	SZ_1GB
 
 /*
  * Address space till 128TB is mapped without any hint
@@ -36,7 +40,7 @@
  * are supported so far.
  */
 
-#define NR_CHUNKS_128TB   8192UL /* Number of 16GB chunks for 128TB */
+#define NR_CHUNKS_128TB   ((128 * SZ_1TB) / MAP_CHUNK_SIZE) /* Number of chunks for 128TB */
 #define NR_CHUNKS_256TB   (NR_CHUNKS_128TB * 2UL)
 #define NR_CHUNKS_384TB   (NR_CHUNKS_128TB * 3UL)