[LTP] [PATCH] memcg/memcontrol05: add cgroup v2 task migration charge accounting test

[LTP] [PATCH] memcg/memcontrol05: add cgroup v2 task migration charge accounting test

[Pavithra]

Verify that in cgroup v2, memory charges remain pinned to the cgroup
that allocated them when a task migrates, and that new allocations after
migration are charged to the destination cgroup.

Signed-off-by: Pavithra <pavrampu@linux.ibm.com>
---
 runtest/controllers                           |   1 +
 testcases/kernel/controllers/memcg/.gitignore |   1 +
 .../kernel/controllers/memcg/memcontrol05.c   | 160 ++++++++++++++++++
 3 files changed, 162 insertions(+)
 create mode 100644 testcases/kernel/controllers/memcg/memcontrol05.c

diff --git a/runtest/controllers b/runtest/controllers
index 93c52c439..a9050ef0e 100644
--- a/runtest/controllers
+++ b/runtest/controllers
@@ -24,6 +24,7 @@ memcontrol01 memcontrol01
 memcontrol02 memcontrol02
 memcontrol03 memcontrol03
 memcontrol04 memcontrol04
+memcontrol05 memcontrol05
 
 cgroup_fj_function_debug cgroup_fj_function.sh debug
 cgroup_fj_function_cpuset cgroup_fj_function.sh cpuset
diff --git a/testcases/kernel/controllers/memcg/.gitignore b/testcases/kernel/controllers/memcg/.gitignore
index 3883cede6..8b9f6005c 100644
--- a/testcases/kernel/controllers/memcg/.gitignore
+++ b/testcases/kernel/controllers/memcg/.gitignore
@@ -9,3 +9,4 @@ memcontrol01
 memcontrol02
 memcontrol03
 memcontrol04
+memcontrol05
diff --git a/testcases/kernel/controllers/memcg/memcontrol05.c b/testcases/kernel/controllers/memcg/memcontrol05.c
new file mode 100644
index 000000000..96621c478
--- /dev/null
+++ b/testcases/kernel/controllers/memcg/memcontrol05.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2026 IBM
+ * Author : Pavithra <pavrampu@linux.ibm.com>
+ */
+
+/*\
+ * Origin: testcases/kernel/controllers/memctl/memctl_testplan.txt
+ * Verify memory controller charge accounting during task migration.
+ *
+ * Two child cgroups (group_a, group_b) are created under the test cgroup.
+ * A worker process is placed in group_a and allocates a known amount of
+ * anonymous memory, touching every page to ensure physical allocation.
+ *
+ * Test 1 - No charge transfer on migration:
+ *   The worker is migrated to group_b by writing its PID to
+ *   group_b/cgroup.procs. In cgroup v2 memory charges are never
+ *   transferred on task migration; they remain pinned to the cgroup
+ *   that allocated them. group_b/memory.current must not increase
+ *   beyond its baseline after the migration.
+ *
+ * Test 2 - New allocations charged to destination cgroup:
+ *   After migration the worker allocates an additional chunk of memory.
+ *   This new allocation must be charged to group_b, so
+ *   group_b/memory.current must increase from the post-migration
+ *   baseline.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include "tst_test.h"
+#include "memcontrol_common.h"
+
+#define ALLOC_SIZE	MB(60)
+#define ALLOC_SIZE2	MB(20)
+
+enum checkpoints {
+	WORKER_ALLOC_DONE,
+	WORKER_RESUME,
+	WORKER_ALLOC2_DONE,
+	WORKER_EXIT,
+};
+
+static struct tst_cg_group *group_a;
+static struct tst_cg_group *group_b;
+static bool worker_resumed;
+
+static void worker(void)
+{
+	char *buf1, *buf2;
+
+	SAFE_CG_PRINTF(group_a, "cgroup.procs", "%d", getpid());
+
+	buf1 = SAFE_MMAP(NULL, ALLOC_SIZE, PROT_READ | PROT_WRITE,
+			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
+
+	TST_CHECKPOINT_WAKE(WORKER_ALLOC_DONE);
+
+	TST_CHECKPOINT_WAIT(WORKER_RESUME);
+
+	buf2 = SAFE_MMAP(NULL, ALLOC_SIZE2, PROT_READ | PROT_WRITE,
+			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
+
+	TST_CHECKPOINT_WAKE(WORKER_ALLOC2_DONE);
+
+	TST_CHECKPOINT_WAIT(WORKER_EXIT);
+
+	SAFE_MUNMAP(buf1, ALLOC_SIZE);
+	SAFE_MUNMAP(buf2, ALLOC_SIZE2);
+}
+
+static void test_memcg_task_migration(void)
+{
+	pid_t pid;
+	long baseline_b, after_migrate, after_alloc2, current_a;
+	worker_resumed = false;
+
+	group_a = tst_cg_group_mk(tst_cg, "group_a");
+	group_b = tst_cg_group_mk(tst_cg, "group_b");
+
+	SAFE_CG_SCANF(group_b, "memory.current", "%ld", &baseline_b);
+	tst_res(TINFO, "group_b baseline memory.current=%ld", baseline_b);
+
+	pid = SAFE_FORK();
+	if (!pid) {
+		worker();
+		exit(0);
+	}
+
+	TST_CHECKPOINT_WAIT(WORKER_ALLOC_DONE);
+
+	SAFE_CG_SCANF(group_a, "memory.current", "%ld", &current_a);
+	tst_res(TINFO, "group_a memory.current=%ld after alloc", current_a);
+	if (current_a < (long)ALLOC_SIZE) {
+		tst_res(TFAIL,
+			"group_a memory.current (%ld) < ALLOC_SIZE (%ld)",
+			current_a, (long)ALLOC_SIZE);
+		goto done;
+	}
+	tst_res(TPASS,
+		"group_a memory.current (%ld) >= ALLOC_SIZE (%ld)",
+		current_a, (long)ALLOC_SIZE);
+
+	SAFE_CG_PRINTF(group_b, "cgroup.procs", "%d", pid);
+	tst_res(TINFO, "Migrated worker PID %d to group_b", pid);
+
+	SAFE_CG_SCANF(group_b, "memory.current", "%ld", &after_migrate);
+	tst_res(TINFO,
+		"group_b memory.current=%ld after migration (baseline=%ld)",
+		after_migrate, baseline_b);
+
+	TST_EXP_EXPR(after_migrate <= baseline_b + (long)MB(4),
+		     "group_b memory.current (%ld) not increased after migration (baseline=%ld)",
+		     after_migrate, baseline_b);
+
+	TST_CHECKPOINT_WAKE(WORKER_RESUME);
+	worker_resumed = true;
+	TST_CHECKPOINT_WAIT(WORKER_ALLOC2_DONE);
+
+	SAFE_CG_SCANF(group_b, "memory.current", "%ld", &after_alloc2);
+	tst_res(TINFO, "group_b memory.current=%ld after second alloc (baseline=%ld)",
+		after_alloc2, after_migrate);
+
+	TST_EXP_EXPR(after_alloc2 >= after_migrate + (long)ALLOC_SIZE2,
+		     "group_b memory.current (%ld) increased by >= ALLOC_SIZE2 (%ld)",
+		     after_alloc2, (long)ALLOC_SIZE2);
+
+done:
+	if (!worker_resumed) {
+		TST_CHECKPOINT_WAKE(WORKER_RESUME);
+		TST_CHECKPOINT_WAIT(WORKER_ALLOC2_DONE);
+	}
+	TST_CHECKPOINT_WAKE(WORKER_EXIT);
+	tst_reap_children();
+
+	group_a = tst_cg_group_rm(group_a);
+	group_b = tst_cg_group_rm(group_b);
+}
+
+static void cleanup(void)
+{
+	if (group_a)
+		group_a = tst_cg_group_rm(group_a);
+	if (group_b)
+		group_b = tst_cg_group_rm(group_b);
+}
+
+static struct tst_test test = {
+	.test_all	= test_memcg_task_migration,
+	.cleanup	= cleanup,
+	.forks_child	= 1,
+	.needs_root	= 1,
+	.needs_checkpoints = 1,
+	.needs_cgroup_ver  = TST_CG_V2,
+	.needs_cgroup_ctrls = (const char *const []){ "memory", NULL },
+};
-- 
2.55.0


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Re: [LTP] memcg/memcontrol05: add cgroup v2 task migration charge accounting test

[linuxtestproject.agent]

Hi Pavithra,

On Aug 4, 2026, Pavithra wrote:
> memcg/memcontrol05: add cgroup v2 task migration charge accounting test

> 	buf1 = SAFE_MMAP(NULL, ALLOC_SIZE, PROT_READ | PROT_WRITE,
> 			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
>
> 	TST_CHECKPOINT_WAKE(WORKER_ALLOC_DONE);
> [...]
> 	buf2 = SAFE_MMAP(NULL, ALLOC_SIZE2, PROT_READ | PROT_WRITE,
> 			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
>
> 	TST_CHECKPOINT_WAKE(WORKER_ALLOC2_DONE);

Could these mappings be populated by explicitly writing one byte per page,
and could the test declare an appropriate .min_mem_avail requirement?

mmap(2) states that mmap() does not fail when MAP_POPULATE cannot populate
the whole mapping. Linux 7.2 also discards mm_populate() errors. Under memory
pressure, the parent can therefore report TFAIL for an incomplete allocation
even though cgroup migration accounting is correct. The test needs 80 MB, but
currently has no memory prerequisite to turn that condition into TCONF.

> 	pid_t pid;
> 	long baseline_b, after_migrate, after_alloc2, current_a;
> 	worker_resumed = false;

Could a blank line be added after the declarations? check-memcontrol05
reports:

  memcontrol05.c:80: WARNING: Missing a blank line after declarations

>  * Two child cgroups (group_a, group_b) are created under the test cgroup.
>  * A worker process is placed in group_a and allocates a known amount of
> [...]
>  *   group_b/cgroup.procs. In cgroup v2 memory charges are never
> [...]
>  *   that allocated them. group_b/memory.current must not increase

Could identifiers and file names in this exported RST block use double
backticks as required for inline literals?

> 	.needs_root	= 1,

Could the description also state why root is required? Root-only tests must
document the reason; here it is needed to create cgroups and move the worker
through cgroup.procs.

Verdict - Needs revision

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