[LTP] [PATCH v8] memcg/memcontrol05: add cgroup v2 task migration charge accounting test

[LTP] [PATCH v8] 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>
---
v7 -> v8:
- use values_close() for post-migration baseline check
- check after_alloc2 >= ALLOC_SIZE2 for destination charge
Link to v7: https://lore.kernel.org/ltp/20260830173408.261946-1-pavrampu@linux.ibm.com/
---
 runtest/controllers                           |   1 +
 testcases/kernel/controllers/memcg/.gitignore |   1 +
 .../kernel/controllers/memcg/memcontrol05.c   | 161 ++++++++++++++++++
 3 files changed, 163 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..fb82bfbdb
--- /dev/null
+++ b/testcases/kernel/controllers/memcg/memcontrol05.c
@@ -0,0 +1,161 @@
+// 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.
+ * Root is required to create cgroup subdirectories and to write a PID
+ * into ``cgroup.procs`` to migrate the worker between cgroups.
+ *
+ * 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 remain close
+ *   to 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 be at least the size of the new allocation.
+ */
+
+#define _GNU_SOURCE
+
+#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)
+#define MIN_MEM_AVAIL	128
+
+static struct tst_cg_group *group_a;
+static struct tst_cg_group *group_b;
+static pid_t worker_pid;
+
+static void touch_pages(char *buf, size_t size)
+{
+	size_t i;
+
+	for (i = 0; i < size; i += getpagesize())
+		buf[i] = 1;
+}
+
+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, -1, 0);
+	touch_pages(buf1, ALLOC_SIZE);
+
+	TST_CHECKPOINT_WAKE_AND_WAIT(0);
+
+	buf2 = SAFE_MMAP(NULL, ALLOC_SIZE2, PROT_READ | PROT_WRITE,
+			 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	touch_pages(buf2, ALLOC_SIZE2);
+
+	TST_CHECKPOINT_WAKE(0);
+
+	pause();
+}
+
+static void test_memcg_task_migration(void)
+{
+	long baseline_b, after_migrate, after_migrate_a, after_alloc2, current_a;
+
+	worker_pid = 0;
+
+	group_a = tst_cg_group_mk(tst_cg, "group_a");
+	group_b = tst_cg_group_mk(tst_cg, "group_b");
+
+	if (SAFE_CG_HAS(tst_cg, "memory.swap.max")) {
+		SAFE_CG_PRINT(group_a, "memory.swap.max", "0");
+		SAFE_CG_PRINT(group_b, "memory.swap.max", "0");
+	}
+
+	SAFE_CG_SCANF(group_b, "memory.current", "%ld", &baseline_b);
+	tst_res(TINFO, "group_b baseline memory.current=%ld", baseline_b);
+
+	worker_pid = SAFE_FORK();
+	if (!worker_pid) {
+		worker();
+		exit(0);
+	}
+
+	TST_CHECKPOINT_WAIT(0);
+
+	SAFE_CG_SCANF(group_a, "memory.current", "%ld", &current_a);
+	TST_EXP_LE_LU(ALLOC_SIZE, current_a);
+
+	SAFE_CG_PRINTF(group_b, "cgroup.procs", "%d", worker_pid);
+	tst_res(TINFO, "Migrated worker PID %d to group_b", worker_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(values_close(after_migrate, baseline_b, 5),
+		     "group_b memory.current (%ld) ~= baseline (%ld)",
+		     after_migrate, baseline_b);
+
+	SAFE_CG_SCANF(group_a, "memory.current", "%ld", &after_migrate_a);
+	tst_res(TINFO, "group_a memory.current=%ld after migration", after_migrate_a);
+	TST_EXP_EXPR(after_migrate_a >= (long)ALLOC_SIZE,
+		     "group_a memory.current (%ld) still holds pre-migration charges (>= ALLOC_SIZE %ld)",
+		     after_migrate_a, (long)ALLOC_SIZE);
+
+	TST_CHECKPOINT_WAKE_AND_WAIT(0);
+
+	SAFE_CG_SCANF(group_b, "memory.current", "%ld", &after_alloc2);
+	tst_res(TINFO, "group_b memory.current=%ld after second alloc",
+		after_alloc2);
+
+	TST_EXP_EXPR(after_alloc2 >= (long)ALLOC_SIZE2,
+		     "group_b memory.current (%ld) >= ALLOC_SIZE2 (%ld)",
+		     after_alloc2, (long)ALLOC_SIZE2);
+
+	SAFE_KILL(worker_pid, SIGKILL);
+	SAFE_WAITPID(worker_pid, NULL, 0);
+	worker_pid = 0;
+
+	group_a = tst_cg_group_rm(group_a);
+	group_b = tst_cg_group_rm(group_b);
+}
+
+static void cleanup(void)
+{
+	if (worker_pid) {
+		SAFE_KILL(worker_pid, SIGKILL);
+		SAFE_WAITPID(worker_pid, NULL, 0);
+	}
+
+	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 },
+	.min_mem_avail	= MIN_MEM_AVAIL,
+};
-- 
2.56.0


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

[linuxtestproject.agent]

Hi Pavithra,

On Sun Nov 8 11:50:34 2026 +0530, Pavithra <pavrampu@linux.ibm.com> wrote:
> memcg/memcontrol05: add cgroup v2 task migration charge accounting test

Verdict - Reviewed

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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Re: [LTP] [PATCH v8] memcg/memcontrol05: add cgroup v2 task migration charge accounting test

[Michal Koutný via ltp]

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Hello.

On Sun, Nov 08, 2026 at 11:50:34AM +0530, Pavithra <pavrampu@linux.ibm.com> wrote:
> 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.

The staticness of memory charges is "non-functional" feature of cgroup
v2. Could you explain more the real word motivation behind this case?

(Each such testcase is subject to noise and it's good to understand
what/why are the expectations.)

Thanks,
Michal

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