selftests/vm: 10x speedup for hmm-tests

This patch reduces the running time for hmm-tests from about 10+ seconds,
to just under 1.0 second, for an approximately 10x speedup.  That brings
it in line with most of the other tests in selftests/vm, which mostly run
in < 1 sec.

This is done with a one-line change that simply reduces the number of
iterations of several tests, from 256, to 10.  Thanks to Ralph Campbell
for suggesting changing NTIMES as a way to get the speedup.
Suggested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: SeongJae Park <sj38.park@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Link: https://lkml.kernel.org/r/20201003011721.44238-1-jhubbard@nvidia.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/hmm-tests.c

@@ -45,7 +45,7 @@ struct hmm_buffer {
 #define TWOMEG		(1 << 21)
 #define HMM_BUFFER_SIZE (1024 << 12)
 #define HMM_PATH_MAX    64
-#define NTIMES		256
+#define NTIMES		10
 
 #define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))