[PATCH v2 5/5] selftests/mm: retry migration failures for the full runtime

[Muhammad Usama Anjum]

move_pages() is best effort and can temporarily fail when concurrent
faults race with page unmapping. A busy shared-anon workload can exhaust
the current 100 retries long before the intended 20-second runtime and
produce a false failure.

Use the full runtime as the retry window. Since the initial page location
is unknown, require it to reach both alternating NUMA targets to confirm
that cross-node migration made progress despite transient contention.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
---
Changes since v1:
- Retry per-page failures for the full runtime
- Verify that both alternating NUMA targets are reached
---
 tools/testing/selftests/mm/migration.c | 39 ++++++++++++++------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
index 29f7492453d43..4d55a424058a9 100644
--- a/tools/testing/selftests/mm/migration.c
+++ b/tools/testing/selftests/mm/migration.c
@@ -7,7 +7,7 @@
 #include "kselftest_harness.h"
 #include "hugepage_settings.h"
 
-#include <strings.h>
+#include <string.h>
 #include <pthread.h>
 #include <numa.h>
 #include <numaif.h>
@@ -20,7 +20,6 @@
 
 #define TWOMEG		(2<<20)
 #define RUNTIME		(20)
-#define MAX_RETRIES	100
 #define ALIGN(x, a)	(((x) + (a - 1)) & (~((a) - 1)))
 
 HUGETLB_SETUP_DEFAULT_PAGES(1)
@@ -110,7 +109,7 @@ int migrate(uint64_t *ptr, int n1, int n2)
 	int ret, tmp;
 	int status = 0;
 	struct timespec ts1, ts2;
-	int failures = 0;
+	int success = 0;
 
 	if (clock_gettime(CLOCK_MONOTONIC, &ts1))
 		return -1;
@@ -119,29 +118,33 @@ int migrate(uint64_t *ptr, int n1, int n2)
 		if (clock_gettime(CLOCK_MONOTONIC, &ts2))
 			return -1;
 
-		if (ts2.tv_sec - ts1.tv_sec >= RUNTIME)
-			return 0;
+		if (ts2.tv_sec - ts1.tv_sec >= RUNTIME) {
+			/* Reaching both targets verifies a cross-node move. */
+			if (success >= 2)
+				return 0;
+			else
+				return -2;
+		}
 
 		ret = move_pages(0, 1, (void **) &ptr, &n2, &status,
 				MPOL_MF_MOVE_ALL);
-		if (ret) {
-			if (ret > 0) {
-				/* Migration is best effort; try again */
-				if (++failures < MAX_RETRIES)
-					continue;
-				printf("Didn't migrate %d pages\n", ret);
-			}
-			else
-				perror("Couldn't migrate pages");
-			return -2;
+		if (ret < 0) {
+			perror("Couldn't migrate pages");
+			return ret;
 		}
-		failures = 0;
+		/* Migration is best effort. Try again */
+		if (ret > 0 || status < 0)
+			continue;
+		if (status != n2) {
+			printf("Page is on node %d instead of target node %d\n",
+			       status, n2);
+			return status;
+		}
+		success++;
 		tmp = n2;
 		n2 = n1;
 		n1 = tmp;
 	}
-
-	return 0;
 }
 
 void *access_mem(void *ptr)
-- 
2.47.3