move_pages12: compacting memory before each test loop

These simple steps are added to prepare the system's memory state
for the test, aiming to increase the test's reliability and
consistency by starting from a clean and defragmented memory state.

To reduce accidental failures on small (1.5G) RAM system:

  7 tst_test.c:1558: TINFO: Timeout per run is 0h 21m 00s
  8 move_pages12.c:273: TINFO: Free RAM 1542656 kB
  9 move_pages12.c:289: TINFO: Increasing 16384kB hugepages pool on node 0 to 4
  10 move_pages12.c:299: TINFO: Increasing 16384kB hugepages pool on node 1 to 4
  11 move_pages12.c:216: TINFO: Allocating and freeing 4 hugepages on node 0
  12 move_pages12.c:216: TINFO: Allocating and freeing 4 hugepages on node 1
  13 move_pages12.c:207: TPASS: Bug not reproduced
  14 move_pages12.c:106: TFAIL: madvise failed: ENOMEM (12)
  ...<repeats 741 times>...
  756 move_pages12.c:207: TPASS: Bug not reproduced

Note:
  This is a single hugetlb test without invoking the hugetlb-lib of LTP,
  so we add the compacting memory/cache steps additionally.

Signed-off-by: Li Wang <[email protected]>
Reviewed-by: Petr Vorel <[email protected]>

testcases/kernel/syscalls/move_pages/move_pages12.c

@@ -154,6 +154,8 @@ static void do_test(unsigned int n)
 	pid_t cpid = -1;
 	int status;
 
+	SAFE_FILE_PRINTF("/proc/sys/vm/compact_memory", "1");
+
 	addr = SAFE_MMAP(NULL, tcases[n].tpages * hpsz, PROT_READ | PROT_WRITE,
 		MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
 
@@ -269,6 +271,7 @@ static void setup(void)
 	pgsz = (int)get_page_size();
 	SAFE_FILE_LINES_SCANF(PATH_MEMINFO, "Hugepagesize: %d", &hpsz);
 
+	SAFE_FILE_PRINTF("/proc/sys/vm/drop_caches", "3");
 	SAFE_FILE_LINES_SCANF(PATH_MEMINFO, "MemFree: %ld", &memfree);
 	tst_res(TINFO, "Free RAM %ld kB", memfree);