[PATCH v2 2/3] selftests: cgroup: refactor proactive reclaim code to reclaim_until()

[Yosry Ahmed <yosryahmed@google.com>]

Refactor the code that drives writing to memory.reclaim (retrying, error
handling, etc) from test_memcg_reclaim() to a helper called
reclaim_until(), which proactively reclaims from a memcg until its
usage reaches a certain value.

This will be used in a following patch in another test.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
---
 .../selftests/cgroup/test_memcontrol.c        | 85 +++++++++++--------
 1 file changed, 49 insertions(+), 36 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index 8833359556f3..d4182e94945e 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -645,6 +645,53 @@ static int test_memcg_max(const char *root)
 	return ret;
 }
 
+/* Reclaim from @memcg until usage reaches @goal_usage */
+static bool reclaim_until(const char *memcg, long goal_usage)
+{
+	char buf[64];
+	int retries = 5;
+	int err;
+	long current, to_reclaim;
+
+	/* Nothing to do here */
+	if (cg_read_long(memcg, "memory.current") <= goal_usage)
+		return true;
+
+	while (true) {
+		current = cg_read_long(memcg, "memory.current");
+		to_reclaim = current - goal_usage;
+
+		/*
+		 * We only keep looping if we get -EAGAIN, which means we could
+		 * not reclaim the full amount. This means we got -EAGAIN when
+		 * we actually reclaimed the requested amount, so fail.
+		 */
+		if (to_reclaim <= 0)
+			break;
+
+		snprintf(buf, sizeof(buf), "%ld", to_reclaim);
+		err = cg_write(memcg, "memory.reclaim", buf);
+		if (!err) {
+			/*
+			 * If writing succeeds, then the written amount should have been
+			 * fully reclaimed (and maybe more).
+			 */
+			current = cg_read_long(memcg, "memory.current");
+			if (!values_close(current, goal_usage, 3) && current > goal_usage)
+				break;
+			return true;
+		}
+
+		/* The kernel could not reclaim the full amount, try again. */
+		if (err == -EAGAIN && retries--)
+			continue;
+
+		/* We got an unexpected error or ran out of retries. */
+		break;
+	}
+	return false;
+}
+
 /*
  * This test checks that memory.reclaim reclaims the given
  * amount of memory (from both anon and file, if possible).
@@ -653,8 +700,7 @@ static int test_memcg_reclaim(const char *root)
 {
 	int ret = KSFT_FAIL, fd, retries;
 	char *memcg;
-	long current, expected_usage, to_reclaim;
-	char buf[64];
+	long current, expected_usage;
 
 	memcg = cg_name(root, "memcg_test");
 	if (!memcg)
@@ -705,41 +751,8 @@ static int test_memcg_reclaim(const char *root)
 	 * Reclaim until current reaches 30M, this makes sure we hit both anon
 	 * and file if swap is enabled.
 	 */
-	retries = 5;
-	while (true) {
-		int err;
-
-		current = cg_read_long(memcg, "memory.current");
-		to_reclaim = current - MB(30);
-
-		/*
-		 * We only keep looping if we get EAGAIN, which means we could
-		 * not reclaim the full amount.
-		 */
-		if (to_reclaim <= 0)
-			goto cleanup;
-
-
-		snprintf(buf, sizeof(buf), "%ld", to_reclaim);
-		err = cg_write(memcg, "memory.reclaim", buf);
-		if (!err) {
-			/*
-			 * If writing succeeds, then the written amount should have been
-			 * fully reclaimed (and maybe more).
-			 */
-			current = cg_read_long(memcg, "memory.current");
-			if (!values_close(current, MB(30), 3) && current > MB(30))
-				goto cleanup;
-			break;
-		}
-
-		/* The kernel could not reclaim the full amount, try again. */
-		if (err == -EAGAIN && retries--)
-			continue;
-
-		/* We got an unexpected error or ran out of retries. */
+	if (!reclaim_until(memcg, MB(30)))
 		goto cleanup;
-	}
 
 	ret = KSFT_PASS;
 cleanup:
-- 
2.38.1.584.g0f3c55d4c2-goog