[RFC PATCH bpf-next v4 00/12] mm: memcontrol: Add BPF hooks for memory controller

[RFC PATCH bpf-next v4 00/12] mm: memcontrol: Add BPF hooks for memory controller

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

eBPF infrastructure provides rich visibility into system performance
metrics through various tracepoints and statistics.
This patch series introduces BPF struct_ops for the memory controller.
Then the eBPF program can help the system control the memory controller
based on system performance metrics, thereby improving the utilization
of system memory resources while ensuring memory limits are respected.

The following example illustrates how memcg eBPF can improve memory
utilization in some scenarios.
The example running on x86_64 QEMU (10 CPUs, 4GB RAM), using a
file in tmpfs on the host as a swap device to reduce I/O impact.
root@ubuntu:~# cat /proc/sys/vm/swappiness
60
This the high priority memcg.
root@ubuntu:~# mkdir /sys/fs/cgroup/high
This the low priority memcg.
root@ubuntu:~# mkdir /sys/fs/cgroup/low
root@ubuntu:~# free
               total        used        free      shared  buff/cache   available
Mem:         4007276      392320     3684940         908      101476     3614956
Swap:       10485756           0    10485756

First, The following test uses memory.low to reduce the likelihood of tasks in
high-priority memory cgroups being reclaimed.
root@ubuntu:~# echo $((3 * 1024 * 1024 * 1024)) > /sys/fs/cgroup/high/memory.low
root@ubuntu:~# cgexec -g memory:low stress-ng --vm 4 --vm-keep \
--vm-bytes $((3 * 1024 * 1024 * 1024)) \
--vm-method all --seed 2025 --metrics -t 60 \
& cgexec -g memory:high stress-ng --vm 4 --vm-keep \
--vm-bytes $((3 * 1024 * 1024 * 1024)) \
--vm-method all --seed 2025 --metrics -t 60
[1] 1176
stress-ng: info:  [1177] setting to a 1 min, 0 secs run per stressor
stress-ng: info:  [1176] setting to a 1 min, 0 secs run per stressor
stress-ng: info:  [1177] dispatching hogs: 4 vm
stress-ng: info:  [1176] dispatching hogs: 4 vm
stress-ng: metrc: [1177] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s CPU used per       RSS Max
stress-ng: metrc: [1177]                           (secs)    (secs)    (secs)   (real time) (usr+sys time) instance (%)          (KB)
stress-ng: metrc: [1177] vm             27047770     60.07    217.79      8.87    450289.91      119330.63        94.34        886936
stress-ng: info:  [1177] skipped: 0
stress-ng: info:  [1177] passed: 4: vm (4)
stress-ng: info:  [1177] failed: 0
stress-ng: info:  [1177] metrics untrustworthy: 0
stress-ng: info:  [1177] successful run completed in 1 min, 0.07 secs
stress-ng: metrc: [1176] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s CPU used per       RSS Max
stress-ng: metrc: [1176]                           (secs)    (secs)    (secs)   (real time) (usr+sys time) instance (%)          (KB)
stress-ng: metrc: [1176] vm               679754     60.12     11.82     72.78     11307.18        8034.42        35.18        469884
stress-ng: info:  [1176] skipped: 0
stress-ng: info:  [1176] passed: 4: vm (4)
stress-ng: info:  [1176] failed: 0
stress-ng: info:  [1176] metrics untrustworthy: 0
stress-ng: info:  [1176] successful run completed in 1 min, 0.13 secs
[1]+  Done                    cgexec -g memory:low stress-ng --vm 4 --vm-keep --vm-bytes $((3 * 1024 * 1024 * 1024)) --vm-method all --seed 2025 --metrics -t 60


The following test continues to use memory.low to reduce the likelihood
of tasks in high-priority memory cgroups (memcg) being reclaimed.
In this scenario, a Python script within the high-priority memcg simulates
a low-load task.
As a result, the Python script's performance is not affected by memory
reclamation (as it sleeps after allocating memory).
However, the performance of stress-ng is still impacted due to
the memory.low setting.

root@ubuntu:~# cgexec -g memory:low stress-ng --vm 4 --vm-keep \
--vm-bytes $((3 * 1024 * 1024 * 1024)) \
--vm-method all --seed 2025 --metrics -t 60 \
& cgexec -g memory:high python3 -c \
"import time; a = bytearray(3*1024*1024*1024); time.sleep(62)"
[1] 1196
stress-ng: info:  [1196] setting to a 1 min, 0 secs run per stressor
stress-ng: info:  [1196] dispatching hogs: 4 vm
stress-ng: metrc: [1196] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s CPU used per       RSS Max
stress-ng: metrc: [1196]                           (secs)    (secs)    (secs)   (real time) (usr+sys time) instance (%)          (KB)
stress-ng: metrc: [1196] vm               886893     60.10     17.76     56.61     14756.92       11925.69        30.94        788676
stress-ng: info:  [1196] skipped: 0
stress-ng: info:  [1196] passed: 4: vm (4)
stress-ng: info:  [1196] failed: 0
stress-ng: info:  [1196] metrics untrustworthy: 0
stress-ng: info:  [1196] successful run completed in 1 min, 0.10 secs
[1]+  Done                    cgexec -g memory:low stress-ng --vm 4 --vm-keep --vm-bytes $((3 * 1024 * 1024 * 1024)) --vm-method all --seed 2025 --metrics -t 60
root@ubuntu:~# echo 0 > /sys/fs/cgroup/high/memory.low

Now, we switch to using the memcg eBPF program for memory priority control.
memcg is a test program added to samples/bpf in this patch series.
It loads memcg.bpf.c into the kernel.
memcg.bpf.c monitors PGFAULT events in the high-priority memory cgroup.
When the number of events triggered within one second exceeds a predefined
threshold, the eBPF hook for the memory cgroup activates its control for
one second.

The following command configures the high-priority memory cgroup to
return below_min during memory reclamation if the number of PGFAULT
events per second exceeds one.
root@ubuntu:~# ./memcg --low_path=/sys/fs/cgroup/low \
     --high_path=/sys/fs/cgroup/high \
     --threshold=1 --use_below_min
Successfully attached!

root@ubuntu:~# cgexec -g memory:low stress-ng --vm 4 --vm-keep \
--vm-bytes $((3 * 1024 * 1024 * 1024)) \
--vm-method all --seed 2025 --metrics -t 60 \
& cgexec -g memory:high stress-ng --vm 4 --vm-keep \
--vm-bytes $((3 * 1024 * 1024 * 1024)) \
--vm-method all --seed 2025 --metrics -t 60
[1] 1220
stress-ng: info:  [1220] setting to a 1 min, 0 secs run per stressor
stress-ng: info:  [1221] setting to a 1 min, 0 secs run per stressor
stress-ng: info:  [1220] dispatching hogs: 4 vm
stress-ng: info:  [1221] dispatching hogs: 4 vm
stress-ng: metrc: [1221] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s CPU used per       RSS Max
stress-ng: metrc: [1221]                           (secs)    (secs)    (secs)   (real time) (usr+sys time) instance (%)          (KB)
stress-ng: metrc: [1221] vm             24295240     60.08    221.36      7.64    404392.49      106095.60        95.29        886684
stress-ng: info:  [1221] skipped: 0
stress-ng: info:  [1221] passed: 4: vm (4)
stress-ng: info:  [1221] failed: 0
stress-ng: info:  [1221] metrics untrustworthy: 0
stress-ng: info:  [1221] successful run completed in 1 min, 0.11 secs
stress-ng: metrc: [1220] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s CPU used per       RSS Max
stress-ng: metrc: [1220]                           (secs)    (secs)    (secs)   (real time) (usr+sys time) instance (%)          (KB)
stress-ng: metrc: [1220] vm               685732     60.13     11.69     75.98     11403.88        7822.30        36.45        496496
stress-ng: info:  [1220] skipped: 0
stress-ng: info:  [1220] passed: 4: vm (4)
stress-ng: info:  [1220] failed: 0
stress-ng: info:  [1220] metrics untrustworthy: 0
stress-ng: info:  [1220] successful run completed in 1 min, 0.14 secs
[1]+  Done                    cgexec -g memory:low stress-ng --vm 4 --vm-keep --vm-bytes $((3 * 1024 * 1024 * 1024)) --vm-method all --seed 2025 --metrics -t 60

This test demonstrates that because the Python process within the
high-priority memory cgroup is sleeping after memory allocation, 
no page fault events occur.
As a result, the stress-ng process in the low-priority memory cgroup
achieves normal memory performance.
root@ubuntu:~# cgexec -g memory:low stress-ng --vm 4 --vm-keep \
--vm-bytes $((3 * 1024 * 1024 * 1024)) \
--vm-method all --seed 2025 --metrics -t 60 \
& cgexec -g memory:high python3 -c \
"import time; a = bytearray(3*1024*1024*1024); time.sleep(62)"
[1] 1238
stress-ng: info:  [1238] setting to a 1 min, 0 secs run per stressor
stress-ng: info:  [1238] dispatching hogs: 4 vm
stress-ng: metrc: [1238] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s CPU used per       RSS Max
stress-ng: metrc: [1238]                           (secs)    (secs)    (secs)   (real time) (usr+sys time) instance (%)          (KB)
stress-ng: metrc: [1238] vm             33107485     60.08    205.41     13.19    551082.91      151448.44        90.97        886064
stress-ng: info:  [1238] skipped: 0
stress-ng: info:  [1238] passed: 4: vm (4)
stress-ng: info:  [1238] failed: 0
stress-ng: info:  [1238] metrics untrustworthy: 0
stress-ng: info:  [1238] successful run completed in 1 min, 0.09 secs

In this patch series, I've incorporated a portion of Roman's patch in
[1] to ensure the entire series can be compiled cleanly with bpf-next.
I made some modifications to bpf_struct_ops_link_create
in "bpf: Pass flags in bpf_link_create for struct_ops" and
"libbpf: Support passing user-defined flags for struct_ops" to allow
the flags parameter to be passed into the kernel.
With this change, patch "mm/bpf: Add BPF_F_ALLOW_OVERRIDE support for
memcg_bpf_ops" enables BPF_F_ALLOW_OVERRIDE support for memcg_bpf_ops.

Patch "mm: memcontrol: Add BPF struct_ops for memory controller"
introduces BPF struct_ops support to the memory controller, enabling
custom and dynamic control over memory pressure. This is achieved
through a new struct_ops type, `memcg_bpf_ops`.
The `memcg_bpf_ops` struct provides the following hooks:
- `get_high_delay_ms`: Returns a custom throttling delay in
  milliseconds for a cgroup that has breached its `memory.high`
  limit. This is the primary mechanism for BPF-driven throttling.
- `below_low`: Overrides the `memory.low` protection check. If this
  hook returns true, the cgroup is considered to be protected by its
  `memory.low` setting, regardless of its actual usage.
- `below_min`: Similar to `below_low`, this overrides the `memory.min`
  protection check.
- `handle_cgroup_online`/`offline`: Callbacks invoked when a cgroup
  with an attached program comes online or goes offline, allowing for
  state management.

Patch "samples/bpf: Add memcg priority control example" introduces
the programs memcg.c and memcg.bpf.c that were used in the previous
examples.

Changelog:
v4:
Fix the issues acccording to the comments of bot+bof-ci.
According to the comments of JP Kobryn, move exit(0) from
real_test_memcg_ops_child_work to real_test_memcg_ops.
Fix the issues in the function bpf_memcg_ops_reg.
v3:
According to the comments of Michal Koutný and Chen Ridong, update hooks
to get_high_delay_ms, below_low, below_min, handle_cgroup_online and
handle_cgroup_offline.
According to the comments of Michal Koutný, add BPF_F_ALLOW_OVERRIDE
support to memcg_bpf_ops.
v2:
According to the comments of Tejun Heo, rebased on Roman Gushchin's BPF
OOM patch series [1] and added hierarchical delegation support.
According to the comments of Roman Gushchin and Michal Hocko, Designed
concrete use case scenarios and provided test results.

[1] https://lore.kernel.org/lkml/20251027231727.472628-1-roman.gushchin@linux.dev/

Hui Zhu (7):
  bpf: Pass flags in bpf_link_create for struct_ops
  libbpf: Support passing user-defined flags for struct_ops
  mm: memcontrol: Add BPF struct_ops for memory controller
  selftests/bpf: Add tests for memcg_bpf_ops
  mm/bpf: Add BPF_F_ALLOW_OVERRIDE support for memcg_bpf_ops
  selftests/bpf: Add test for memcg_bpf_ops hierarchies
  samples/bpf: Add memcg priority control example

Roman Gushchin (5):
  bpf: move bpf_struct_ops_link into bpf.h
  bpf: initial support for attaching struct ops to cgroups
  bpf: mark struct oom_control's memcg field as TRUSTED_OR_NULL
  mm: define mem_cgroup_get_from_ino() outside of CONFIG_SHRINKER_DEBUG
  libbpf: introduce bpf_map__attach_struct_ops_opts()

 MAINTAINERS                                   |   4 +
 include/linux/bpf.h                           |   8 +
 include/linux/memcontrol.h                    | 111 +++-
 kernel/bpf/bpf_struct_ops.c                   |  22 +-
 kernel/bpf/verifier.c                         |   5 +
 mm/bpf_memcontrol.c                           | 276 +++++++-
 mm/memcontrol.c                               |  34 +-
 samples/bpf/.gitignore                        |   1 +
 samples/bpf/Makefile                          |   8 +-
 samples/bpf/memcg.bpf.c                       | 129 ++++
 samples/bpf/memcg.c                           | 327 ++++++++++
 tools/include/uapi/linux/bpf.h                |   2 +-
 tools/lib/bpf/bpf.c                           |   8 +
 tools/lib/bpf/libbpf.c                        |  19 +-
 tools/lib/bpf/libbpf.h                        |  14 +
 tools/lib/bpf/libbpf.map                      |   1 +
 .../selftests/bpf/prog_tests/memcg_ops.c      | 611 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/memcg_ops.c | 129 ++++
 18 files changed, 1682 insertions(+), 27 deletions(-)
 create mode 100644 samples/bpf/memcg.bpf.c
 create mode 100644 samples/bpf/memcg.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/memcg_ops.c
 create mode 100644 tools/testing/selftests/bpf/progs/memcg_ops.c

-- 
2.43.0

[RFC PATCH bpf-next v4 01/12] bpf: move bpf_struct_ops_link into bpf.h

[Hui Zhu]

From: Roman Gushchin <roman.gushchin@linux.dev>

Move struct bpf_struct_ops_link's definition into bpf.h,
where other custom bpf links definitions are.

It's necessary to access its members from outside of generic
bpf_struct_ops implementation, which will be done by following
patches in the series.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 include/linux/bpf.h         | 6 ++++++
 kernel/bpf/bpf_struct_ops.c | 6 ------
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4427c6e98331..899dd911dc82 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1891,6 +1891,12 @@ struct bpf_raw_tp_link {
 	u64 cookie;
 };
 
+struct bpf_struct_ops_link {
+	struct bpf_link link;
+	struct bpf_map __rcu *map;
+	wait_queue_head_t wait_hup;
+};
+
 struct bpf_link_primer {
 	struct bpf_link *link;
 	struct file *file;
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index c43346cb3d76..de01cf3025b3 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -55,12 +55,6 @@ struct bpf_struct_ops_map {
 	struct bpf_struct_ops_value kvalue;
 };
 
-struct bpf_struct_ops_link {
-	struct bpf_link link;
-	struct bpf_map __rcu *map;
-	wait_queue_head_t wait_hup;
-};
-
 static DEFINE_MUTEX(update_mutex);
 
 #define VALUE_PREFIX "bpf_struct_ops_"
-- 
2.43.0

[RFC PATCH bpf-next v4 02/12] bpf: initial support for attaching struct ops to cgroups

[Hui Zhu]

From: Roman Gushchin <roman.gushchin@linux.dev>

When a struct ops is being attached and a bpf link is created,
allow to pass a cgroup fd using bpf attr, so that struct ops
can be attached to a cgroup instead of globally.

Attached struct ops doesn't hold a reference to the cgroup,
only preserves cgroup id.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 include/linux/bpf.h         |  1 +
 kernel/bpf/bpf_struct_ops.c | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 899dd911dc82..720055d1dbce 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1895,6 +1895,7 @@ struct bpf_struct_ops_link {
 	struct bpf_link link;
 	struct bpf_map __rcu *map;
 	wait_queue_head_t wait_hup;
+	u64 cgroup_id;
 };
 
 struct bpf_link_primer {
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index de01cf3025b3..c807793e7633 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -13,6 +13,7 @@
 #include <linux/btf_ids.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/poll.h>
+#include <linux/cgroup.h>
 
 struct bpf_struct_ops_value {
 	struct bpf_struct_ops_common_value common;
@@ -1377,6 +1378,20 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
 	}
 	bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL,
 		      attr->link_create.attach_type);
+#ifdef CONFIG_CGROUPS
+	if (attr->link_create.cgroup.relative_fd) {
+		struct cgroup *cgrp;
+
+		cgrp = cgroup_get_from_fd(attr->link_create.cgroup.relative_fd);
+		if (IS_ERR(cgrp)) {
+			err = PTR_ERR(cgrp);
+			goto err_out;
+		}
+
+		link->cgroup_id = cgroup_id(cgrp);
+		cgroup_put(cgrp);
+	}
+#endif /* CONFIG_CGROUPS */
 
 	err = bpf_link_prime(&link->link, &link_primer);
 	if (err)
-- 
2.43.0

[RFC PATCH bpf-next v4 03/12] bpf: mark struct oom_control's memcg field as TRUSTED_OR_NULL

[Hui Zhu]

From: Roman Gushchin <roman.gushchin@linux.dev>

Struct oom_control is used to describe the OOM context.
It's memcg field defines the scope of OOM: it's NULL for global
OOMs and a valid memcg pointer for memcg-scoped OOMs.
Teach bpf verifier to recognize it as trusted or NULL pointer.
It will provide the bpf OOM handler a trusted memcg pointer,
which for example is required for iterating the memcg's subtree.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c2f2650db9fd..cca36edb460d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7242,6 +7242,10 @@ BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct vm_area_struct) {
 	struct file *vm_file;
 };
 
+BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct oom_control) {
+	struct mem_cgroup *memcg;
+};
+
 static bool type_is_rcu(struct bpf_verifier_env *env,
 			struct bpf_reg_state *reg,
 			const char *field_name, u32 btf_id)
@@ -7284,6 +7288,7 @@ static bool type_is_trusted_or_null(struct bpf_verifier_env *env,
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct dentry));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct vm_area_struct));
+	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct oom_control));
 
 	return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id,
 					  "__safe_trusted_or_null");
-- 
2.43.0

[RFC PATCH bpf-next v4 04/12] mm: define mem_cgroup_get_from_ino() outside of CONFIG_SHRINKER_DEBUG

[Hui Zhu]

From: Roman Gushchin <roman.gushchin@linux.dev>

mem_cgroup_get_from_ino() can be reused by the BPF OOM implementation,
but currently depends on CONFIG_SHRINKER_DEBUG. Remove this dependency.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 include/linux/memcontrol.h | 4 ++--
 mm/memcontrol.c            | 2 --
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 229ac9835adb..f3b8c71870d8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -833,9 +833,9 @@ static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg)
 {
 	return memcg ? cgroup_ino(memcg->css.cgroup) : 0;
 }
+#endif
 
 struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino);
-#endif
 
 static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
 {
@@ -1298,12 +1298,12 @@ static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg)
 {
 	return 0;
 }
+#endif
 
 static inline struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
 {
 	return NULL;
 }
-#endif
 
 static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3808845bc8cc..1f74fce27677 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3658,7 +3658,6 @@ struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 	return xa_load(&mem_cgroup_ids, id);
 }
 
-#ifdef CONFIG_SHRINKER_DEBUG
 struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
 {
 	struct cgroup *cgrp;
@@ -3679,7 +3678,6 @@ struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
 
 	return memcg;
 }
-#endif
 
 static void free_mem_cgroup_per_node_info(struct mem_cgroup_per_node *pn)
 {
-- 
2.43.0

[RFC PATCH bpf-next v4 05/12] libbpf: introduce bpf_map__attach_struct_ops_opts()

[Hui Zhu]

From: Roman Gushchin <roman.gushchin@linux.dev>

Introduce bpf_map__attach_struct_ops_opts(), an extended version of
bpf_map__attach_struct_ops(), which takes additional struct
bpf_struct_ops_opts argument.

struct bpf_struct_ops_opts has the relative_fd member, which allows
to pass an additional file descriptor argument. It can be used to
attach struct ops maps to cgroups.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 tools/lib/bpf/bpf.c      |  8 ++++++++
 tools/lib/bpf/libbpf.c   | 18 ++++++++++++++++--
 tools/lib/bpf/libbpf.h   | 14 ++++++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 4 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 5846de364209..84a53c594f48 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -884,6 +884,14 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, cgroup))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_STRUCT_OPS:
+		relative_fd = OPTS_GET(opts, cgroup.relative_fd, 0);
+		attr.link_create.cgroup.relative_fd = relative_fd;
+		attr.link_create.cgroup.expected_revision =
+			OPTS_GET(opts, cgroup.expected_revision, 0);
+		if (!OPTS_ZEROED(opts, cgroup))
+			return libbpf_err(-EINVAL);
+		break;
 	default:
 		if (!OPTS_ZEROED(opts, flags))
 			return libbpf_err(-EINVAL);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0c8bf0b5cce4..70a00da54ff5 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -13462,12 +13462,19 @@ static int bpf_link__detach_struct_ops(struct bpf_link *link)
 	return close(link->fd);
 }
 
-struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
+struct bpf_link *bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
+						 const struct bpf_struct_ops_opts *opts)
 {
+	DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts);
 	struct bpf_link_struct_ops *link;
 	__u32 zero = 0;
 	int err, fd;
 
+	if (!OPTS_VALID(opts, bpf_struct_ops_opts)) {
+		pr_warn("map '%s': invalid opts\n", map->name);
+		return libbpf_err_ptr(-EINVAL);
+	}
+
 	if (!bpf_map__is_struct_ops(map)) {
 		pr_warn("map '%s': can't attach non-struct_ops map\n", map->name);
 		return libbpf_err_ptr(-EINVAL);
@@ -13503,7 +13510,9 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 		return &link->link;
 	}
 
-	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, NULL);
+	link_opts.cgroup.relative_fd = OPTS_GET(opts, relative_fd, 0);
+
+	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, &link_opts);
 	if (fd < 0) {
 		free(link);
 		return libbpf_err_ptr(fd);
@@ -13515,6 +13524,11 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 	return &link->link;
 }
 
+struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
+{
+	return bpf_map__attach_struct_ops_opts(map, NULL);
+}
+
 /*
  * Swap the back struct_ops of a link with a new struct_ops map.
  */
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index dfc37a615578..5aef44bcfcc2 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -920,6 +920,20 @@ bpf_program__attach_cgroup_opts(const struct bpf_program *prog, int cgroup_fd,
 struct bpf_map;
 
 LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
+
+struct bpf_struct_ops_opts {
+	/* size of this struct, for forward/backward compatibility */
+	size_t sz;
+	__u32 flags;
+	__u32 relative_fd;
+	__u64 expected_revision;
+	size_t :0;
+};
+#define bpf_struct_ops_opts__last_field expected_revision
+
+LIBBPF_API struct bpf_link *
+bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
+				const struct bpf_struct_ops_opts *opts);
 LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
 
 struct bpf_iter_attach_opts {
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d18fbcea7578..4779190c97b6 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -454,4 +454,5 @@ LIBBPF_1.7.0 {
 		bpf_prog_assoc_struct_ops;
 		bpf_program__assoc_struct_ops;
 		btf__permute;
+		bpf_map__attach_struct_ops_opts;
 } LIBBPF_1.6.0;
-- 
2.43.0

[RFC PATCH bpf-next v4 06/12] bpf: Pass flags in bpf_link_create for struct_ops

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

To support features like allowing overrides in cgroup hierarchies,
we need a way to pass flags from userspace to the kernel when
attaching a struct_ops.

Extend `bpf_struct_ops_link` to include a `flags` field. This field
is populated from `attr->link_create.flags` during link creation. This
will allow struct_ops implementations, such as the upcoming memory
controller ops, to interpret these flags and modify their attachment
behavior accordingly.

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 include/linux/bpf.h            | 1 +
 kernel/bpf/bpf_struct_ops.c    | 1 +
 tools/include/uapi/linux/bpf.h | 2 +-
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 720055d1dbce..13c933cfc614 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1896,6 +1896,7 @@ struct bpf_struct_ops_link {
 	struct bpf_map __rcu *map;
 	wait_queue_head_t wait_hup;
 	u64 cgroup_id;
+	u32 flags;
 };
 
 struct bpf_link_primer {
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index c807793e7633..0df608c88403 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -1392,6 +1392,7 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
 		cgroup_put(cgrp);
 	}
 #endif /* CONFIG_CGROUPS */
+	link->flags = attr->link_create.flags;
 
 	err = bpf_link_prime(&link->link, &link_primer);
 	if (err)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 3ca7d76e05f0..4e1c5d6d91ae 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1185,7 +1185,7 @@ enum bpf_perf_event_type {
 	BPF_PERF_EVENT_EVENT = 6,
 };
 
-/* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
+/* cgroup-bpf attach flags used in BPF_PROG_ATTACH and BPF_LINK_CREATE command
  *
  * NONE(default): No further bpf programs allowed in the subtree.
  *
-- 
2.43.0

[RFC PATCH bpf-next v4 07/12] libbpf: Support passing user-defined flags for struct_ops

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

Building on the previous change that added flags to the kernel's link
creation path, this patch exposes this functionality through libbpf.

The `bpf_struct_ops_opts` struct is extended with a `flags` member,
which is then passed to the `bpf_link_create` syscall within
`bpf_map__attach_struct_ops_opts`.

This enables userspace applications to pass flags, such as
`BPF_F_ALLOW_OVERRIDE`, when attaching struct_ops to cgroups,
providing more control over the attachment behavior in nested
hierarchies.

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 tools/lib/bpf/libbpf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 70a00da54ff5..06c936bad211 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -13511,6 +13511,7 @@ struct bpf_link *bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
 	}
 
 	link_opts.cgroup.relative_fd = OPTS_GET(opts, relative_fd, 0);
+	link_opts.flags = OPTS_GET(opts, flags, 0);
 
 	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, &link_opts);
 	if (fd < 0) {
-- 
2.43.0

[RFC PATCH bpf-next v4 08/12] mm: memcontrol: Add BPF struct_ops for memory controller

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

Introduce BPF struct_ops support to the memory controller, enabling
custom and dynamic control over memory pressure. This is achieved
through a new struct_ops type, `memcg_bpf_ops`.

This new interface allows a BPF program to implement hooks that
influence a memory cgroup's behavior. The `memcg_bpf_ops` struct
provides the following hooks:

- `get_high_delay_ms`: Returns a custom throttling delay in
  milliseconds for a cgroup that has breached its `memory.high`
  limit. This is the primary mechanism for BPF-driven throttling.

- `below_low`: Overrides the `memory.low` protection check. If this
  hook returns true, the cgroup is considered to be protected by its
  `memory.low` setting, regardless of its actual usage.

- `below_min`: Similar to `below_low`, this overrides the `memory.min`
  protection check.

- `handle_cgroup_online`/`offline`: Callbacks invoked when a cgroup
  with an attached program comes online or goes offline, allowing for
  state management.

This patch integrates these hooks into the core memory control logic.
The `get_high_delay_ms` value is incorporated into charge paths like
`try_charge_memcg` and the high-limit handler
`__mem_cgroup_handle_over_high`. The `below_low` and `below_min`
hooks are checked within their respective protection functions.

Lifecycle management is handled to ensure BPF programs are correctly
inherited by child cgroups and cleaned up on detachment. SRCU is used
to protect concurrent access to the `memcg->bpf_ops` pointer.

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 include/linux/memcontrol.h | 106 ++++++++++++++-
 mm/bpf_memcontrol.c        | 255 ++++++++++++++++++++++++++++++++++++-
 mm/memcontrol.c            |  32 +++--
 3 files changed, 380 insertions(+), 13 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f3b8c71870d8..1083be5d0362 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -181,6 +181,37 @@ struct obj_cgroup {
 	};
 };
 
+#ifdef CONFIG_BPF_SYSCALL
+/**
+ * struct memcg_bpf_ops - BPF callbacks for memory cgroup operations
+ * @handle_cgroup_online: Called when a cgroup comes online
+ * @handle_cgroup_offline: Called when a cgroup goes offline
+ * @below_low: Override memory.low protection check. If this callback returns
+ *             true, mem_cgroup_below_low() will return true immediately without
+ *             performing the standard comparison. If it returns false, the
+ *             original memory.low threshold comparison will proceed normally.
+ * @below_min: Override memory.min protection check. If this callback returns
+ *             true, mem_cgroup_below_min() will return true immediately without
+ *             performing the standard comparison. If it returns false, the
+ *             original memory.min threshold comparison will proceed normally.
+ * @get_high_delay_ms: Return custom throttle delay in milliseconds
+ *
+ * This structure defines the interface for BPF programs to customize
+ * memory cgroup behavior through struct_ops programs.
+ */
+struct memcg_bpf_ops {
+	void (*handle_cgroup_online)(struct mem_cgroup *memcg);
+
+	void (*handle_cgroup_offline)(struct mem_cgroup *memcg);
+
+	bool (*below_low)(struct mem_cgroup *memcg);
+
+	bool (*below_min)(struct mem_cgroup *memcg);
+
+	unsigned int (*get_high_delay_ms)(struct mem_cgroup *memcg);
+};
+#endif /* CONFIG_BPF_SYSCALL */
+
 /*
  * The memory controller data structure. The memory controller controls both
  * page cache and RSS per cgroup. We would eventually like to provide
@@ -321,6 +352,10 @@ struct mem_cgroup {
 	spinlock_t event_list_lock;
 #endif /* CONFIG_MEMCG_V1 */
 
+#ifdef CONFIG_BPF_SYSCALL
+	struct memcg_bpf_ops *bpf_ops;
+#endif
+
 	struct mem_cgroup_per_node *nodeinfo[];
 };
 
@@ -554,6 +589,66 @@ static inline bool mem_cgroup_disabled(void)
 	return !cgroup_subsys_enabled(memory_cgrp_subsys);
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+
+/* SRCU for protecting concurrent access to memcg->bpf_ops */
+extern struct srcu_struct memcg_bpf_srcu;
+
+/**
+ * BPF_MEMCG_CALL - Safely invoke a BPF memcg callback
+ * @memcg: The memory cgroup
+ * @op: The operation name (struct member)
+ * @default_val: Default return value if no BPF program attached
+ *
+ * This macro safely calls a BPF callback under SRCU protection.
+ */
+#define BPF_MEMCG_CALL(memcg, op, default_val) ({		\
+	typeof(default_val) __ret = (default_val);		\
+	struct memcg_bpf_ops *__ops;				\
+	int __idx;						\
+								\
+	__idx = srcu_read_lock(&memcg_bpf_srcu);		\
+	__ops = READ_ONCE((memcg)->bpf_ops);			\
+	if (__ops && __ops->op)					\
+		__ret = __ops->op(memcg);			\
+	srcu_read_unlock(&memcg_bpf_srcu, __idx);		\
+	__ret;							\
+})
+
+static inline bool bpf_memcg_below_low(struct mem_cgroup *memcg)
+{
+	return BPF_MEMCG_CALL(memcg, below_low, false);
+}
+
+static inline bool bpf_memcg_below_min(struct mem_cgroup *memcg)
+{
+	return BPF_MEMCG_CALL(memcg, below_min, false);
+}
+
+static inline unsigned long bpf_memcg_get_high_delay(struct mem_cgroup *memcg)
+{
+	unsigned int ret;
+
+	ret = BPF_MEMCG_CALL(memcg, get_high_delay_ms, 0U);
+	return msecs_to_jiffies(ret);
+}
+
+#undef BPF_MEMCG_CALL
+
+extern void memcontrol_bpf_online(struct mem_cgroup *memcg);
+extern void memcontrol_bpf_offline(struct mem_cgroup *memcg);
+
+#else /* CONFIG_BPF_SYSCALL */
+
+static inline unsigned long
+bpf_memcg_get_high_delay(struct mem_cgroup *memcg) { return 0; }
+static inline bpf_memcg_below_low(struct mem_cgroup *memcg) { return false; }
+static inline bpf_memcg_below_min(struct mem_cgroup *memcg) { return false; }
+static inline void memcontrol_bpf_online(struct mem_cgroup *memcg) { }
+static inline void memcontrol_bpf_offline(struct mem_cgroup *memcg) { }
+
+#endif /* CONFIG_BPF_SYSCALL */
+
 static inline void mem_cgroup_protection(struct mem_cgroup *root,
 					 struct mem_cgroup *memcg,
 					 unsigned long *min,
@@ -625,6 +720,9 @@ static inline bool mem_cgroup_below_low(struct mem_cgroup *target,
 	if (mem_cgroup_unprotected(target, memcg))
 		return false;
 
+	if (bpf_memcg_below_low(memcg))
+		return true;
+
 	return READ_ONCE(memcg->memory.elow) >=
 		page_counter_read(&memcg->memory);
 }
@@ -635,6 +733,9 @@ static inline bool mem_cgroup_below_min(struct mem_cgroup *target,
 	if (mem_cgroup_unprotected(target, memcg))
 		return false;
 
+	if (bpf_memcg_below_min(memcg))
+		return true;
+
 	return READ_ONCE(memcg->memory.emin) >=
 		page_counter_read(&memcg->memory);
 }
@@ -909,12 +1010,13 @@ unsigned long mem_cgroup_get_zone_lru_size(struct lruvec *lruvec,
 	return READ_ONCE(mz->lru_zone_size[zone_idx][lru]);
 }
 
-void __mem_cgroup_handle_over_high(gfp_t gfp_mask);
+void __mem_cgroup_handle_over_high(gfp_t gfp_mask,
+				   unsigned long bpf_high_delay);
 
 static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 {
 	if (unlikely(current->memcg_nr_pages_over_high))
-		__mem_cgroup_handle_over_high(gfp_mask);
+		__mem_cgroup_handle_over_high(gfp_mask, 0);
 }
 
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
index 716df49d7647..20c5c3552ce3 100644
--- a/mm/bpf_memcontrol.c
+++ b/mm/bpf_memcontrol.c
@@ -8,6 +8,9 @@
 #include <linux/memcontrol.h>
 #include <linux/bpf.h>
 
+/* Protects memcg->bpf_ops pointer for read and write. */
+DEFINE_SRCU(memcg_bpf_srcu);
+
 __bpf_kfunc_start_defs();
 
 /**
@@ -179,15 +182,263 @@ static const struct btf_kfunc_id_set bpf_memcontrol_kfunc_set = {
 	.set            = &bpf_memcontrol_kfuncs,
 };
 
+/**
+ * memcontrol_bpf_online - Inherit BPF programs for a new online cgroup.
+ * @memcg: The memory cgroup that is coming online.
+ *
+ * When a new memcg is brought online, it inherits the BPF programs
+ * attached to its parent. This ensures consistent BPF-based memory
+ * control policies throughout the cgroup hierarchy.
+ *
+ * After inheriting, if the BPF program has an online handler, it is
+ * invoked for the new memcg.
+ */
+void memcontrol_bpf_online(struct mem_cgroup *memcg)
+{
+	int idx;
+	struct memcg_bpf_ops *ops;
+	struct mem_cgroup *parent_memcg;
+
+	/* The root cgroup does not inherit from a parent. */
+	if (mem_cgroup_is_root(memcg))
+		return;
+
+	parent_memcg = parent_mem_cgroup(memcg);
+
+	idx = srcu_read_lock(&memcg_bpf_srcu);
+
+	/* Inherit the BPF program from the parent cgroup. */
+	ops = READ_ONCE(parent_memcg->bpf_ops);
+	if (!ops)
+		goto out;
+
+	WRITE_ONCE(memcg->bpf_ops, ops);
+
+	/*
+	 * If the BPF program implements it, call the online handler to
+	 * allow the program to perform setup tasks for the new cgroup.
+	 */
+	if (!ops->handle_cgroup_online)
+		goto out;
+
+	ops->handle_cgroup_online(memcg);
+
+out:
+	srcu_read_unlock(&memcg_bpf_srcu, idx);
+}
+
+/**
+ * memcontrol_bpf_offline - Run BPF cleanup for an offline cgroup.
+ * @memcg: The memory cgroup that is going offline.
+ *
+ * If a BPF program is attached and implements an offline handler,
+ * it is invoked to perform cleanup tasks before the memcg goes
+ * completely offline.
+ */
+void memcontrol_bpf_offline(struct mem_cgroup *memcg)
+{
+	int idx;
+	struct memcg_bpf_ops *ops;
+
+	idx = srcu_read_lock(&memcg_bpf_srcu);
+
+	ops = READ_ONCE(memcg->bpf_ops);
+	if (!ops || !ops->handle_cgroup_offline)
+		goto out;
+
+	ops->handle_cgroup_offline(memcg);
+
+out:
+	srcu_read_unlock(&memcg_bpf_srcu, idx);
+}
+
+static int memcg_ops_btf_struct_access(struct bpf_verifier_log *log,
+					const struct bpf_reg_state *reg,
+					int off, int size)
+{
+	return -EACCES;
+}
+
+static bool memcg_ops_is_valid_access(int off, int size, enum bpf_access_type type,
+	const struct bpf_prog *prog,
+	struct bpf_insn_access_aux *info)
+{
+	return bpf_tracing_btf_ctx_access(off, size, type, prog, info);
+}
+
+const struct bpf_verifier_ops bpf_memcg_verifier_ops = {
+	.get_func_proto = bpf_base_func_proto,
+	.btf_struct_access = memcg_ops_btf_struct_access,
+	.is_valid_access = memcg_ops_is_valid_access,
+};
+
+static void cfi_handle_cgroup_online(struct mem_cgroup *memcg)
+{
+}
+
+static void cfi_handle_cgroup_offline(struct mem_cgroup *memcg)
+{
+}
+
+static bool cfi_below_low(struct mem_cgroup *memcg)
+{
+	return false;
+}
+
+static bool cfi_below_min(struct mem_cgroup *memcg)
+{
+	return false;
+}
+
+static unsigned int cfi_get_high_delay_ms(struct mem_cgroup *memcg)
+{
+	return 0;
+}
+
+static struct memcg_bpf_ops cfi_bpf_memcg_ops = {
+	.handle_cgroup_online = cfi_handle_cgroup_online,
+	.handle_cgroup_offline = cfi_handle_cgroup_offline,
+	.below_low = cfi_below_low,
+	.below_min = cfi_below_min,
+	.get_high_delay_ms = cfi_get_high_delay_ms,
+};
+
+static int bpf_memcg_ops_init(struct btf *btf)
+{
+	return 0;
+}
+
+static int bpf_memcg_ops_check_member(const struct btf_type *t,
+				const struct btf_member *member,
+				const struct bpf_prog *prog)
+{
+	u32 moff = __btf_member_bit_offset(t, member) / 8;
+
+	switch (moff) {
+	case offsetof(struct memcg_bpf_ops, handle_cgroup_online):
+		break;
+	case offsetof(struct memcg_bpf_ops, handle_cgroup_offline):
+		break;
+	case offsetof(struct memcg_bpf_ops, below_low):
+		break;
+	case offsetof(struct memcg_bpf_ops, below_min):
+		break;
+	case offsetof(struct memcg_bpf_ops, get_high_delay_ms):
+		break;
+	default:
+		if (prog->sleepable)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int bpf_memcg_ops_init_member(const struct btf_type *t,
+				const struct btf_member *member,
+				void *kdata, const void *udata)
+{
+	return 0;
+}
+
+/**
+ * clean_memcg_bpf_ops - Detach BPF programs from a cgroup hierarchy.
+ * @memcg: The root of the cgroup hierarchy to clean.
+ * @ops:   The specific ops struct to detach. If NULL, detach any ops.
+ *
+ * Iterates through all descendant cgroups of @memcg (including itself)
+ * and clears their bpf_ops pointer. This is used when a BPF program
+ * is detached or if attachment fails midway.
+ */
+static void clean_memcg_bpf_ops(struct mem_cgroup *memcg,
+				struct memcg_bpf_ops *ops)
+{
+	struct mem_cgroup *iter = NULL;
+
+	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
+		if (ops) {
+			if (!WARN_ON(READ_ONCE(iter->bpf_ops) != ops))
+				WRITE_ONCE(iter->bpf_ops, NULL);
+		} else
+			WRITE_ONCE(iter->bpf_ops, NULL);
+	}
+}
+
+static int bpf_memcg_ops_reg(void *kdata, struct bpf_link *link)
+{
+	struct bpf_struct_ops_link *ops_link
+		= container_of(link, struct bpf_struct_ops_link, link);
+	struct memcg_bpf_ops *ops = kdata;
+	struct mem_cgroup *memcg, *iter = NULL;
+	int err = 0;
+
+	memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id);
+	if (IS_ERR_OR_NULL(memcg))
+		return PTR_ERR(memcg);
+
+	cgroup_lock();
+	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
+		if (READ_ONCE(iter->bpf_ops)) {
+			mem_cgroup_iter_break(memcg, iter);
+			err = -EBUSY;
+			break;
+		}
+		WRITE_ONCE(iter->bpf_ops, ops);
+	}
+	if (err)
+		clean_memcg_bpf_ops(memcg, NULL);
+	cgroup_unlock();
+
+	mem_cgroup_put(memcg);
+	return err;
+}
+
+/* Unregister the struct ops instance */
+static void bpf_memcg_ops_unreg(void *kdata, struct bpf_link *link)
+{
+	struct bpf_struct_ops_link *ops_link
+		= container_of(link, struct bpf_struct_ops_link, link);
+	struct memcg_bpf_ops *ops = kdata;
+	struct mem_cgroup *memcg;
+
+	memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id);
+	if (IS_ERR_OR_NULL(memcg))
+		goto out;
+
+	cgroup_lock();
+	clean_memcg_bpf_ops(memcg, ops);
+	cgroup_unlock();
+
+	mem_cgroup_put(memcg);
+
+out:
+	synchronize_srcu(&memcg_bpf_srcu);
+}
+
+static struct bpf_struct_ops bpf_memcg_bpf_ops = {
+	.verifier_ops = &bpf_memcg_verifier_ops,
+	.init = bpf_memcg_ops_init,
+	.check_member = bpf_memcg_ops_check_member,
+	.init_member = bpf_memcg_ops_init_member,
+	.reg = bpf_memcg_ops_reg,
+	.unreg = bpf_memcg_ops_unreg,
+	.name = "memcg_bpf_ops",
+	.owner = THIS_MODULE,
+	.cfi_stubs = &cfi_bpf_memcg_ops,
+};
+
 static int __init bpf_memcontrol_init(void)
 {
-	int err;
+	int err, err2;
 
 	err = register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC,
 					&bpf_memcontrol_kfunc_set);
 	if (err)
 		pr_warn("error while registering bpf memcontrol kfuncs: %d", err);
 
-	return err;
+	err2 = register_bpf_struct_ops(&bpf_memcg_bpf_ops, memcg_bpf_ops);
+	if (err2)
+		pr_warn("error while registering memcontrol bpf ops: %d", err2);
+
+	return err ? err : err2;
 }
 late_initcall(bpf_memcontrol_init);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1f74fce27677..8d90575aa77d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2252,7 +2252,8 @@ static unsigned long calculate_high_delay(struct mem_cgroup *memcg,
  * try_charge() (context permitting), as well as from the userland
  * return path where reclaim is always able to block.
  */
-void __mem_cgroup_handle_over_high(gfp_t gfp_mask)
+void
+__mem_cgroup_handle_over_high(gfp_t gfp_mask, unsigned long bpf_high_delay)
 {
 	unsigned long penalty_jiffies;
 	unsigned long pflags;
@@ -2294,11 +2295,15 @@ void __mem_cgroup_handle_over_high(gfp_t gfp_mask)
 	 * memory.high is breached and reclaim is unable to keep up. Throttle
 	 * allocators proactively to slow down excessive growth.
 	 */
-	penalty_jiffies = calculate_high_delay(memcg, nr_pages,
-					       mem_find_max_overage(memcg));
+	if (nr_pages) {
+		penalty_jiffies = calculate_high_delay(
+			memcg, nr_pages, mem_find_max_overage(memcg));
 
-	penalty_jiffies += calculate_high_delay(memcg, nr_pages,
-						swap_find_max_overage(memcg));
+		penalty_jiffies += calculate_high_delay(
+			memcg, nr_pages, swap_find_max_overage(memcg));
+	} else
+		penalty_jiffies = 0;
+	penalty_jiffies = max(penalty_jiffies, bpf_high_delay);
 
 	/*
 	 * Clamp the max delay per usermode return so as to still keep the
@@ -2356,6 +2361,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	bool raised_max_event = false;
 	unsigned long pflags;
 	bool allow_spinning = gfpflags_allow_spinning(gfp_mask);
+	struct mem_cgroup *orig_memcg;
 
 retry:
 	if (consume_stock(memcg, nr_pages))
@@ -2481,6 +2487,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	if (batch > nr_pages)
 		refill_stock(memcg, batch - nr_pages);
 
+	orig_memcg = memcg;
 	/*
 	 * If the hierarchy is above the normal consumption range, schedule
 	 * reclaim on returning to userland.  We can perform reclaim here
@@ -2530,10 +2537,14 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 * kernel. If this is successful, the return path will see it
 	 * when it rechecks the overage and simply bail out.
 	 */
-	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
-	    !(current->flags & PF_MEMALLOC) &&
-	    gfpflags_allow_blocking(gfp_mask))
-		__mem_cgroup_handle_over_high(gfp_mask);
+	if (gfpflags_allow_blocking(gfp_mask)) {
+		unsigned long bpf_high_delay;
+
+		bpf_high_delay = bpf_memcg_get_high_delay(orig_memcg);
+		if (bpf_high_delay ||
+		    current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH)
+			__mem_cgroup_handle_over_high(gfp_mask, bpf_high_delay);
+	}
 	return 0;
 }
 
@@ -3906,6 +3917,8 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	 */
 	xa_store(&mem_cgroup_ids, memcg->id.id, memcg, GFP_KERNEL);
 
+	memcontrol_bpf_online(memcg);
+
 	return 0;
 offline_kmem:
 	memcg_offline_kmem(memcg);
@@ -3925,6 +3938,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 
 	zswap_memcg_offline_cleanup(memcg);
 
+	memcontrol_bpf_offline(memcg);
 	memcg_offline_kmem(memcg);
 	reparent_deferred_split_queue(memcg);
 	reparent_shrinker_deferred(memcg);
-- 
2.43.0

[RFC PATCH bpf-next v4 09/12] selftests/bpf: Add tests for memcg_bpf_ops

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

Add a comprehensive selftest suite for the `memcg_bpf_ops`
functionality. These tests validate that BPF programs can correctly
influence memory cgroup throttling behavior by implementing the new
hooks.

The test suite is added in `prog_tests/memcg_ops.c` and covers
several key scenarios:

1. `test_memcg_ops_over_high`:
   Verifies that a BPF program can trigger throttling on a low-priority
   cgroup by returning a delay from the `get_high_delay_ms` hook when a
   high-priority cgroup is under pressure.

2. `test_memcg_ops_below_low_over_high`:
   Tests the combination of the `below_low` and `get_high_delay_ms`
   hooks, ensuring they work together as expected.

3. `test_memcg_ops_below_min_over_high`:
   Validates the interaction between the `below_min` and
   `get_high_delay_ms` hooks.

The test framework sets up a cgroup hierarchy with high and low
priority groups, attaches BPF programs, runs memory-intensive
workloads, and asserts that the observed throttling (measured by
workload execution time) matches expectations.

The BPF program (`progs/memcg_ops.c`) uses a tracepoint on
`memcg:count_memcg_events` (specifically PGFAULT) to detect memory
pressure and trigger the appropriate hooks in response. This test
suite provides essential validation for the new memory control
mechanisms.

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 MAINTAINERS                                   |   2 +
 .../selftests/bpf/prog_tests/memcg_ops.c      | 541 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/memcg_ops.c | 129 +++++
 3 files changed, 672 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/memcg_ops.c
 create mode 100644 tools/testing/selftests/bpf/progs/memcg_ops.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 491d567f7dc8..7e07bb330eae 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6471,6 +6471,8 @@ F:	mm/memcontrol-v1.h
 F:	mm/page_counter.c
 F:	mm/swap_cgroup.c
 F:	samples/cgroup/*
+F:	tools/testing/selftests/bpf/prog_tests/memcg_ops.c
+F:	tools/testing/selftests/bpf/progs/memcg_ops.c
 F:	tools/testing/selftests/cgroup/memcg_protection.m
 F:	tools/testing/selftests/cgroup/test_hugetlb_memcg.c
 F:	tools/testing/selftests/cgroup/test_kmem.c
diff --git a/tools/testing/selftests/bpf/prog_tests/memcg_ops.c b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
new file mode 100644
index 000000000000..a019ba2387bc
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
@@ -0,0 +1,541 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Memory controller eBPF struct ops test
+ */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "cgroup_helpers.h"
+
+struct local_config {
+	u64 threshold;
+	u64 high_cgroup_id;
+	bool use_below_low;
+	bool use_below_min;
+	unsigned int over_high_ms;
+} local_config;
+
+#include "memcg_ops.skel.h"
+
+#define TRIGGER_THRESHOLD 1
+#define OVER_HIGH_MS 2000
+#define FILE_SIZE (64 * 1024 * 1024ul)
+#define BUFFER_SIZE (4096)
+#define CG_LIMIT (120 * 1024 * 1024ul)
+
+#define CG_DIR "/memcg_ops_test"
+#define CG_HIGH_DIR CG_DIR "/high"
+#define CG_LOW_DIR CG_DIR "/low"
+
+static int
+setup_cgroup(int *high_cgroup_id, int *low_cgroup_fd, int *high_cgroup_fd)
+{
+	int ret;
+	char limit_buf[20];
+
+	ret = setup_cgroup_environment();
+	if (!ASSERT_OK(ret, "setup_cgroup_environment"))
+		goto cleanup;
+
+	ret = create_and_get_cgroup(CG_DIR);
+	if (!ASSERT_GE(ret, 0, "create_and_get_cgroup "CG_DIR))
+		goto cleanup;
+	close(ret);
+	ret = enable_controllers(CG_DIR, "memory");
+	if (!ASSERT_OK(ret, "enable_controllers"))
+		goto cleanup;
+	snprintf(limit_buf, 20, "%ld", CG_LIMIT);
+	ret = write_cgroup_file(CG_DIR, "memory.max", limit_buf);
+	if (!ASSERT_OK(ret, "write_cgroup_file memory.max"))
+		goto cleanup;
+	ret = write_cgroup_file(CG_DIR, "memory.swap.max", "0");
+	if (!ASSERT_OK(ret, "write_cgroup_file memory.swap.max"))
+		goto cleanup;
+
+	ret = create_and_get_cgroup(CG_HIGH_DIR);
+	if (!ASSERT_GE(ret, 0, "create_and_get_cgroup "CG_HIGH_DIR))
+		goto cleanup;
+	if (high_cgroup_fd)
+		*high_cgroup_fd = ret;
+	else
+		close(ret);
+	ret = (int)get_cgroup_id(CG_HIGH_DIR);
+	if (!ASSERT_GE(ret, 0, "get_cgroup_id"))
+		goto cleanup;
+	*high_cgroup_id = ret;
+
+	ret = create_and_get_cgroup(CG_LOW_DIR);
+	if (!ASSERT_GE(ret, 0, "create_and_get_cgroup "CG_LOW_DIR))
+		goto cleanup;
+	if (low_cgroup_fd)
+		*low_cgroup_fd = ret;
+	else
+		close(ret);
+
+	return 0;
+
+cleanup:
+	cleanup_cgroup_environment();
+	return -1;
+}
+
+int write_file(const char *filename)
+{
+	int ret = -1;
+	size_t written = 0;
+	char *buffer;
+	FILE *fp;
+
+	fp = fopen(filename, "wb");
+	if (!fp)
+		goto out;
+
+	buffer = malloc(BUFFER_SIZE);
+	if (!buffer)
+		goto cleanup_fp;
+
+	memset(buffer, 'A', BUFFER_SIZE);
+
+	while (written < FILE_SIZE) {
+		size_t to_write = (FILE_SIZE - written < BUFFER_SIZE) ?
+				   (FILE_SIZE - written) :
+				   BUFFER_SIZE;
+
+		if (fwrite(buffer, 1, to_write, fp) != to_write)
+			goto cleanup;
+		written += to_write;
+	}
+
+	ret = 0;
+cleanup:
+	free(buffer);
+cleanup_fp:
+	fclose(fp);
+out:
+	return ret;
+}
+
+int read_file(const char *filename, int iterations)
+{
+	int ret = -1;
+	long page_size = sysconf(_SC_PAGESIZE);
+	char *p;
+	char *map;
+	size_t i;
+	int fd;
+	struct stat sb;
+
+	fd = open(filename, O_RDONLY);
+	if (fd == -1)
+		goto out;
+
+	if (fstat(fd, &sb) == -1)
+		goto cleanup_fd;
+
+	if (sb.st_size != FILE_SIZE) {
+		fprintf(stderr, "File size mismatch: expected %ld, got %ld\n",
+			FILE_SIZE, sb.st_size);
+		goto cleanup_fd;
+	}
+
+	map = mmap(NULL, FILE_SIZE, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (map == MAP_FAILED)
+		goto cleanup_fd;
+
+	for (int iter = 0; iter < iterations; iter++) {
+		for (i = 0; i < FILE_SIZE; i += page_size) {
+			/* access a byte to trigger page fault */
+			p = &map[i];
+			__asm__ __volatile__("" : : "r"(p) : "memory");
+		}
+
+		if (env.verbosity >= VERBOSE_NORMAL)
+			printf("%s %d %d done\n", __func__, getpid(), iter);
+	}
+
+	if (munmap(map, FILE_SIZE) == -1)
+		goto cleanup_fd;
+
+	ret = 0;
+
+cleanup_fd:
+	close(fd);
+out:
+	return ret;
+}
+
+static void
+real_test_memcg_ops_child_work(const char *cgroup_path,
+			       char *data_filename,
+			       char *time_filename,
+			       int read_times)
+{
+	struct timeval start, end;
+	double elapsed;
+	FILE *fp;
+
+	if (!ASSERT_OK(join_parent_cgroup(cgroup_path), "join_parent_cgroup"))
+		return;
+
+	if (env.verbosity >= VERBOSE_NORMAL)
+		printf("%s %d begin\n", __func__, getpid());
+
+	gettimeofday(&start, NULL);
+
+	if (!ASSERT_OK(write_file(data_filename), "write_file"))
+		return;
+
+	if (env.verbosity >= VERBOSE_NORMAL)
+		printf("%s %d write_file done\n", __func__, getpid());
+
+	if (!ASSERT_OK(read_file(data_filename, read_times), "read_file"))
+		return;
+
+	gettimeofday(&end, NULL);
+
+	elapsed = (end.tv_sec - start.tv_sec) +
+		  (end.tv_usec - start.tv_usec) / 1000000.0;
+
+	if (env.verbosity >= VERBOSE_NORMAL)
+		printf("%s %d end %.6f\n", __func__, getpid(), elapsed);
+
+	fp = fopen(time_filename, "w");
+	if (!ASSERT_OK_PTR(fp, "fopen"))
+		return;
+	fprintf(fp, "%.6f", elapsed);
+	fclose(fp);
+}
+
+static int get_time(char *time_filename, double *time)
+{
+	int ret = -1;
+	FILE *fp;
+	char buf[64];
+
+	fp = fopen(time_filename, "r");
+	if (!ASSERT_OK_PTR(fp, "fopen"))
+		goto out;
+
+	if (!ASSERT_OK_PTR(fgets(buf, sizeof(buf), fp), "fgets"))
+		goto cleanup;
+
+	if (sscanf(buf, "%lf", time) < 0) {
+		PRINT_FAIL("sscanf %s", buf);
+		goto cleanup;
+	}
+
+	ret = 0;
+cleanup:
+	fclose(fp);
+out:
+	return ret;
+}
+
+static void real_test_memcg_ops(int read_times)
+{
+	int ret;
+	char data_file1[] = "/tmp/test_data_XXXXXX";
+	char data_file2[] = "/tmp/test_data_XXXXXX";
+	char time_file1[] = "/tmp/test_time_XXXXXX";
+	char time_file2[] = "/tmp/test_time_XXXXXX";
+	pid_t pid1, pid2;
+	double time1, time2;
+
+	ret = mkstemp(data_file1);
+	if (!ASSERT_GT(ret, 0, "mkstemp"))
+		return;
+	close(ret);
+	ret = mkstemp(data_file2);
+	if (!ASSERT_GT(ret, 0, "mkstemp"))
+		goto cleanup_data_file1;
+	close(ret);
+	ret = mkstemp(time_file1);
+	if (!ASSERT_GT(ret, 0, "mkstemp"))
+		goto cleanup_data_file2;
+	close(ret);
+	ret = mkstemp(time_file2);
+	if (!ASSERT_GT(ret, 0, "mkstemp"))
+		goto cleanup_time_file1;
+	close(ret);
+
+	pid1 = fork();
+	if (!ASSERT_GE(pid1, 0, "fork"))
+		goto cleanup;
+	if (pid1 == 0) {
+		real_test_memcg_ops_child_work(CG_LOW_DIR,
+					       data_file1,
+					       time_file1,
+					       read_times);
+		exit(0);
+	}
+
+	pid2 = fork();
+	if (!ASSERT_GE(pid2, 0, "fork"))
+		goto cleanup;
+	if (pid2 == 0) {
+		real_test_memcg_ops_child_work(CG_HIGH_DIR,
+					       data_file2,
+					       time_file2,
+					       read_times);
+		exit(0);
+	}
+
+	ret = waitpid(pid1, NULL, 0);
+	if (!ASSERT_GT(ret, 0, "waitpid"))
+		goto cleanup;
+
+	ret = waitpid(pid2, NULL, 0);
+	if (!ASSERT_GT(ret, 0, "waitpid"))
+		goto cleanup;
+
+	if (get_time(time_file1, &time1))
+		goto cleanup;
+
+	if (get_time(time_file2, &time2))
+		goto cleanup;
+
+	if (time1 < time2 || time1 - time2 <= 1)
+		PRINT_FAIL("low fast compare time1=%f, time2=%f",
+			   time1, time2);
+
+cleanup:
+	unlink(time_file2);
+cleanup_time_file1:
+	unlink(time_file1);
+cleanup_data_file2:
+	unlink(data_file2);
+cleanup_data_file1:
+	unlink(data_file1);
+}
+
+void test_memcg_ops_over_high(void)
+{
+	int err, map_fd;
+	struct memcg_ops *skel = NULL;
+	struct bpf_map *map;
+	size_t bss_sz;
+	struct memcg_ops__bss *bss_data;
+	__u32 key = 0;
+	struct bpf_program *prog = NULL;
+	struct bpf_link *link = NULL, *link2 = NULL;
+	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
+	int high_cgroup_id, low_cgroup_fd = -1;
+
+	err = setup_cgroup(&high_cgroup_id, &low_cgroup_fd, NULL);
+	if (!ASSERT_OK(err, "setup_cgroup"))
+		goto out;
+
+	skel = memcg_ops__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "memcg_ops__open_and_load"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, ".bss");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name .bss"))
+		goto out;
+
+	map_fd = bpf_map__fd(map);
+	bss_sz = bpf_map__value_size(map);
+	bss_data = malloc(bpf_map__value_size(map));
+	if (!ASSERT_OK_PTR(bss_data, "malloc(bpf_map__value_size(map))"))
+		goto out;
+	memset(bss_data, 0, sizeof(struct local_config));
+	bss_data->local_config.high_cgroup_id = high_cgroup_id;
+	bss_data->local_config.threshold = TRIGGER_THRESHOLD;
+	bss_data->local_config.use_below_low = false;
+	bss_data->local_config.use_below_min = false;
+	bss_data->local_config.over_high_ms = OVER_HIGH_MS;
+	err = bpf_map_update_elem(map_fd, &key, bss_data, BPF_EXIST);
+	free(bss_data);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	prog = bpf_object__find_program_by_name(skel->obj,
+						"handle_count_memcg_events");
+	if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+		goto out;
+
+	link = bpf_program__attach(prog);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, "low_mcg_ops");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name low_mcg_ops"))
+		goto out;
+
+	opts.relative_fd = low_cgroup_fd;
+	link2 = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link2, "bpf_map__attach_struct_ops_opts"))
+		goto out;
+
+	real_test_memcg_ops(5);
+
+out:
+	bpf_link__destroy(link);
+	bpf_link__destroy(link2);
+	memcg_ops__detach(skel);
+	memcg_ops__destroy(skel);
+	close(low_cgroup_fd);
+	cleanup_cgroup_environment();
+}
+
+void test_memcg_ops_below_low_over_high(void)
+{
+	int err, map_fd;
+	struct memcg_ops *skel = NULL;
+	struct bpf_map *map;
+	size_t bss_sz;
+	struct memcg_ops__bss *bss_data;
+	__u32 key = 0;
+	struct bpf_program *prog = NULL;
+	struct bpf_link *link = NULL, *link_high = NULL, *link_low = NULL;
+	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
+	int high_cgroup_id, high_cgroup_fd = -1, low_cgroup_fd = -1;
+
+	err = setup_cgroup(&high_cgroup_id, &low_cgroup_fd, &high_cgroup_fd);
+	if (!ASSERT_OK(err, "setup_cgroup"))
+		goto out;
+
+	skel = memcg_ops__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "memcg_ops__open_and_load"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, ".bss");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name .bss"))
+		goto out;
+
+	map_fd = bpf_map__fd(map);
+	bss_sz = bpf_map__value_size(map);
+	bss_data = malloc(bpf_map__value_size(map));
+	if (!ASSERT_OK_PTR(bss_data, "malloc(bpf_map__value_size(map))"))
+		goto out;
+	memset(bss_data, 0, sizeof(struct local_config));
+	bss_data->local_config.high_cgroup_id = high_cgroup_id;
+	bss_data->local_config.threshold = TRIGGER_THRESHOLD;
+	bss_data->local_config.use_below_low = true;
+	bss_data->local_config.use_below_min = false;
+	bss_data->local_config.over_high_ms = OVER_HIGH_MS;
+	err = bpf_map_update_elem(map_fd, &key, bss_data, BPF_EXIST);
+	free(bss_data);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	prog = bpf_object__find_program_by_name(skel->obj,
+						"handle_count_memcg_events");
+	if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+		goto out;
+
+	link = bpf_program__attach(prog);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, "high_mcg_ops");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name mcg_ops"))
+		goto out;
+	opts.relative_fd = high_cgroup_fd;
+	link_high = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link_high, "bpf_map__attach_struct_ops_opts"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, "low_mcg_ops");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name mcg_ops"))
+		goto out;
+	opts.relative_fd = low_cgroup_fd;
+	link_low = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link_low, "bpf_map__attach_struct_ops_opts"))
+		goto out;
+
+	real_test_memcg_ops(50);
+
+out:
+	bpf_link__destroy(link);
+	bpf_link__destroy(link_high);
+	bpf_link__destroy(link_low);
+	memcg_ops__detach(skel);
+	memcg_ops__destroy(skel);
+	close(high_cgroup_fd);
+	close(low_cgroup_fd);
+	cleanup_cgroup_environment();
+}
+
+void test_memcg_ops_below_min_over_high(void)
+{
+	int err, map_fd;
+	struct memcg_ops *skel = NULL;
+	struct bpf_map *map;
+	size_t bss_sz;
+	struct memcg_ops__bss *bss_data;
+	__u32 key = 0;
+	struct bpf_program *prog = NULL;
+	struct bpf_link *link = NULL, *link_high = NULL, *link_low = NULL;
+	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
+	int high_cgroup_id, high_cgroup_fd = -1, low_cgroup_fd = -1;
+
+	err = setup_cgroup(&high_cgroup_id, &low_cgroup_fd, &high_cgroup_fd);
+	if (!ASSERT_OK(err, "setup_cgroup"))
+		goto out;
+
+	skel = memcg_ops__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "memcg_ops__open_and_load"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, ".bss");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name .bss"))
+		goto out;
+
+	map_fd = bpf_map__fd(map);
+	bss_sz = bpf_map__value_size(map);
+	bss_data = malloc(bpf_map__value_size(map));
+	if (!ASSERT_OK_PTR(bss_data, "malloc(bpf_map__value_size(map))"))
+		goto out;
+	memset(bss_data, 0, sizeof(struct local_config));
+	bss_data->local_config.high_cgroup_id = high_cgroup_id;
+	bss_data->local_config.threshold = TRIGGER_THRESHOLD;
+	bss_data->local_config.use_below_low = false;
+	bss_data->local_config.use_below_min = true;
+	bss_data->local_config.over_high_ms = OVER_HIGH_MS;
+	err = bpf_map_update_elem(map_fd, &key, bss_data, BPF_EXIST);
+	free(bss_data);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	prog = bpf_object__find_program_by_name(skel->obj,
+						"handle_count_memcg_events");
+	if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+		goto out;
+
+	link = bpf_program__attach(prog);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, "high_mcg_ops");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name mcg_ops"))
+		goto out;
+	opts.relative_fd = high_cgroup_fd;
+	link_high = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link_high, "bpf_map__attach_struct_ops_opts"))
+		goto out;
+
+	map = bpf_object__find_map_by_name(skel->obj, "low_mcg_ops");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name mcg_ops"))
+		goto out;
+	opts.relative_fd = low_cgroup_fd;
+	link_low = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link_low, "bpf_map__attach_struct_ops_opts"))
+		goto out;
+
+	real_test_memcg_ops(50);
+
+out:
+	bpf_link__destroy(link);
+	bpf_link__destroy(link_high);
+	bpf_link__destroy(link_low);
+	memcg_ops__detach(skel);
+	memcg_ops__destroy(skel);
+	close(high_cgroup_fd);
+	close(low_cgroup_fd);
+	cleanup_cgroup_environment();
+}
diff --git a/tools/testing/selftests/bpf/progs/memcg_ops.c b/tools/testing/selftests/bpf/progs/memcg_ops.c
new file mode 100644
index 000000000000..44087a206a61
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/memcg_ops.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#define ONE_SECOND_NS	1000000000
+
+struct local_config {
+	u64 threshold;
+	u64 high_cgroup_id;
+	bool use_below_low;
+	bool use_below_min;
+	unsigned int over_high_ms;
+} local_config;
+
+struct AggregationData {
+	u64 sum;
+	u64 window_start_ts;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct AggregationData);
+} aggregation_map SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, u64);
+} trigger_ts_map SEC(".maps");
+
+SEC("tp/memcg/count_memcg_events")
+int
+handle_count_memcg_events(struct trace_event_raw_memcg_rstat_events *ctx)
+{
+	u32 key = 0;
+	struct AggregationData *data;
+	u64 current_ts;
+
+	if (ctx->id != local_config.high_cgroup_id ||
+	    (ctx->item != PGFAULT))
+		goto out;
+
+	data = bpf_map_lookup_elem(&aggregation_map, &key);
+	if (!data)
+		goto out;
+
+	current_ts = bpf_ktime_get_ns();
+
+	if (current_ts - data->window_start_ts < ONE_SECOND_NS) {
+		data->sum += ctx->val;
+	} else {
+		data->window_start_ts = current_ts;
+		data->sum = ctx->val;
+	}
+
+	if (data->sum > local_config.threshold) {
+		bpf_map_update_elem(&trigger_ts_map, &key, &current_ts,
+				    BPF_ANY);
+		data->sum = 0;
+		data->window_start_ts = current_ts;
+	}
+
+out:
+	return 0;
+}
+
+static bool need_threshold(void)
+{
+	u32 key = 0;
+	u64 *trigger_ts;
+	bool ret = false;
+
+	trigger_ts = bpf_map_lookup_elem(&trigger_ts_map, &key);
+	if (!trigger_ts || *trigger_ts == 0)
+		goto out;
+
+	u64 current_ts = bpf_ktime_get_ns();
+
+	if (current_ts - *trigger_ts < ONE_SECOND_NS)
+		ret = true;
+
+out:
+	return ret;
+}
+
+SEC("struct_ops/below_low")
+unsigned int below_low_impl(struct mem_cgroup *memcg)
+{
+	if (!local_config.use_below_low)
+		return false;
+
+	return need_threshold();
+}
+
+SEC("struct_ops/below_min")
+unsigned int below_min_impl(struct mem_cgroup *memcg)
+{
+	if (!local_config.use_below_min)
+		return false;
+
+	return need_threshold();
+}
+
+SEC("struct_ops/get_high_delay_ms")
+unsigned int get_high_delay_ms_impl(struct mem_cgroup *memcg)
+{
+	if (local_config.over_high_ms && need_threshold())
+		return local_config.over_high_ms;
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct memcg_bpf_ops high_mcg_ops = {
+	.below_low = (void *)below_low_impl,
+	.below_min = (void *)below_min_impl,
+};
+
+SEC(".struct_ops.link")
+struct memcg_bpf_ops low_mcg_ops = {
+	.get_high_delay_ms = (void *)get_high_delay_ms_impl,
+};
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.43.0

[RFC PATCH bpf-next v4 10/12] mm/bpf: Add BPF_F_ALLOW_OVERRIDE support for memcg_bpf_ops

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

To allow for more flexible attachment policies in nested cgroup
hierarchies, this patch introduces support for the
`BPF_F_ALLOW_OVERRIDE` flag for `memcg_bpf_ops`.

When a `memcg_bpf_ops` is attached to a cgroup with this flag, it
permits child cgroups to attach their own, different `memcg_bpf_ops`,
overriding the parent's inherited program. Without this flag,
attaching a BPF program to a cgroup that already has one (either
directly or via inheritance) will fail.

The implementation involves:
- Adding a `bpf_ops_flags` field to `struct mem_cgroup`.
- During registration (`bpf_memcg_ops_reg`), checking for existing
  programs and the `BPF_F_ALLOW_OVERRIDE` flag.
- During unregistration (`bpf_memcg_ops_unreg`), correctly restoring
  the parent's BPF program to the cgroup hierarchy.
- Ensuring flags are inherited by child cgroups during online events.

This change enables complex, multi-level policy enforcement where
different subtrees of the cgroup hierarchy can have distinct memory
management BPF programs.

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 include/linux/memcontrol.h |  1 +
 mm/bpf_memcontrol.c        | 83 ++++++++++++++++++++++++--------------
 2 files changed, 53 insertions(+), 31 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1083be5d0362..6e15da44ba35 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -354,6 +354,7 @@ struct mem_cgroup {
 
 #ifdef CONFIG_BPF_SYSCALL
 	struct memcg_bpf_ops *bpf_ops;
+	u32 bpf_ops_flags;
 #endif
 
 	struct mem_cgroup_per_node *nodeinfo[];
diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
index 20c5c3552ce3..756a7d4eb4e3 100644
--- a/mm/bpf_memcontrol.c
+++ b/mm/bpf_memcontrol.c
@@ -213,6 +213,7 @@ void memcontrol_bpf_online(struct mem_cgroup *memcg)
 		goto out;
 
 	WRITE_ONCE(memcg->bpf_ops, ops);
+	memcg->bpf_ops_flags = parent_memcg->bpf_ops_flags;
 
 	/*
 	 * If the BPF program implements it, call the online handler to
@@ -340,52 +341,54 @@ static int bpf_memcg_ops_init_member(const struct btf_type *t,
 	return 0;
 }
 
-/**
- * clean_memcg_bpf_ops - Detach BPF programs from a cgroup hierarchy.
- * @memcg: The root of the cgroup hierarchy to clean.
- * @ops:   The specific ops struct to detach. If NULL, detach any ops.
- *
- * Iterates through all descendant cgroups of @memcg (including itself)
- * and clears their bpf_ops pointer. This is used when a BPF program
- * is detached or if attachment fails midway.
- */
-static void clean_memcg_bpf_ops(struct mem_cgroup *memcg,
-				struct memcg_bpf_ops *ops)
-{
-	struct mem_cgroup *iter = NULL;
-
-	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
-		if (ops) {
-			if (!WARN_ON(READ_ONCE(iter->bpf_ops) != ops))
-				WRITE_ONCE(iter->bpf_ops, NULL);
-		} else
-			WRITE_ONCE(iter->bpf_ops, NULL);
-	}
-}
-
 static int bpf_memcg_ops_reg(void *kdata, struct bpf_link *link)
 {
 	struct bpf_struct_ops_link *ops_link
 		= container_of(link, struct bpf_struct_ops_link, link);
-	struct memcg_bpf_ops *ops = kdata;
+	struct memcg_bpf_ops *ops = kdata, *parent_ops = NULL;
 	struct mem_cgroup *memcg, *iter = NULL;
 	int err = 0;
 
+	if (ops_link->flags & ~BPF_F_ALLOW_OVERRIDE) {
+		pr_err("attach only support BPF_F_ALLOW_OVERRIDE\n");
+		return -EOPNOTSUPP;
+	}
+
 	memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id);
 	if (IS_ERR_OR_NULL(memcg))
 		return PTR_ERR(memcg);
 
 	cgroup_lock();
-	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
-		if (READ_ONCE(iter->bpf_ops)) {
-			mem_cgroup_iter_break(memcg, iter);
+
+	if (READ_ONCE(memcg->bpf_ops)) {
+		/* Check if bpf_ops of the parent is BPF_F_ALLOW_OVERRIDE. */
+		if (memcg->bpf_ops_flags & BPF_F_ALLOW_OVERRIDE) {
+			iter = parent_mem_cgroup(memcg);
+			if (!iter || READ_ONCE(iter->bpf_ops) !=
+				     READ_ONCE(memcg->bpf_ops))
+				goto busy_out;
+
+			parent_ops = READ_ONCE(memcg->bpf_ops);
+		} else {
+busy_out:
 			err = -EBUSY;
-			break;
+			goto unlock_out;
+		}
+	}
+
+	iter = NULL;
+	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
+		struct memcg_bpf_ops *iter_ops = READ_ONCE(iter->bpf_ops);
+
+		if (iter_ops && iter_ops != parent_ops) {
+			/* cannot override existing bpf_ops of sub-cgroup. */
+			continue;
 		}
 		WRITE_ONCE(iter->bpf_ops, ops);
+		iter->bpf_ops_flags = ops_link->flags;
 	}
-	if (err)
-		clean_memcg_bpf_ops(memcg, NULL);
+
+unlock_out:
 	cgroup_unlock();
 
 	mem_cgroup_put(memcg);
@@ -399,13 +402,31 @@ static void bpf_memcg_ops_unreg(void *kdata, struct bpf_link *link)
 		= container_of(link, struct bpf_struct_ops_link, link);
 	struct memcg_bpf_ops *ops = kdata;
 	struct mem_cgroup *memcg;
+	struct mem_cgroup *iter;
+	struct memcg_bpf_ops *parent_bpf_ops = NULL;
+	u32 parent_bpf_ops_flags = 0;
 
 	memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id);
 	if (IS_ERR_OR_NULL(memcg))
 		goto out;
 
 	cgroup_lock();
-	clean_memcg_bpf_ops(memcg, ops);
+
+	/* Get the parent bpf_ops and bpf_ops_flags */
+	iter = parent_mem_cgroup(memcg);
+	if (iter) {
+		parent_bpf_ops = READ_ONCE(iter->bpf_ops);
+		parent_bpf_ops_flags = iter->bpf_ops_flags;
+	}
+
+	iter = NULL;
+	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
+		if (READ_ONCE(iter->bpf_ops) == ops) {
+			WRITE_ONCE(iter->bpf_ops, parent_bpf_ops);
+			iter->bpf_ops_flags = parent_bpf_ops_flags;
+		}
+	}
+
 	cgroup_unlock();
 
 	mem_cgroup_put(memcg);
-- 
2.43.0

[RFC PATCH bpf-next v4 11/12] selftests/bpf: Add test for memcg_bpf_ops hierarchies

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

Add a new selftest, `test_memcg_ops_hierarchies`, to validate the
behavior of attaching `memcg_bpf_ops` in a nested cgroup hierarchy,
specifically testing the `BPF_F_ALLOW_OVERRIDE` flag.

The test case performs the following steps:
1. Creates a three-level deep cgroup hierarchy: `/cg`, `/cg/cg`, and
   `/cg/cg/cg`.
2. Attaches a BPF struct_ops to the top-level cgroup (`/cg`) with the
   `BPF_F_ALLOW_OVERRIDE` flag.
3. Successfully attaches a new struct_ops to the middle cgroup
   (`/cg/cg`) without the flag, overriding the inherited one.
4. Asserts that attaching another struct_ops to the deepest cgroup
   (`/cg/cg/cg`) fails with -EBUSY, because its parent did not specify
   `BPF_F_ALLOW_OVERRIDE`.

This test ensures that the attachment logic correctly enforces the
override rules across a cgroup subtree.

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 .../selftests/bpf/prog_tests/memcg_ops.c      | 70 +++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/memcg_ops.c b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
index a019ba2387bc..08ac97752ac9 100644
--- a/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
+++ b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
@@ -539,3 +539,73 @@ void test_memcg_ops_below_min_over_high(void)
 	close(low_cgroup_fd);
 	cleanup_cgroup_environment();
 }
+
+void test_memcg_ops_hierarchies(void)
+{
+	int ret, first = -1, second = -1, third = -1;
+	struct memcg_ops *skel;
+	struct bpf_map *map;
+	struct bpf_link *link1 = NULL, *link2 = NULL, *link3 = NULL;
+	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
+
+	ret = setup_cgroup_environment();
+	if (!ASSERT_OK(ret, "setup_cgroup_environment"))
+		goto cleanup;
+
+	first = create_and_get_cgroup("/cg");
+	if (!ASSERT_GE(first, 0, "create_and_get_cgroup /cg"))
+		goto cleanup;
+	ret = enable_controllers("/cg", "memory");
+	if (!ASSERT_OK(ret, "enable_controllers"))
+		goto cleanup;
+
+	second = create_and_get_cgroup("/cg/cg");
+	if (!ASSERT_GE(second, 0, "create_and_get_cgroup /cg/cg"))
+		goto cleanup;
+	ret = enable_controllers("/cg/cg", "memory");
+	if (!ASSERT_OK(ret, "enable_controllers"))
+		goto cleanup;
+
+	third = create_and_get_cgroup("/cg/cg/cg");
+	if (!ASSERT_GE(third, 0, "create_and_get_cgroup /cg/cg/cg"))
+		goto cleanup;
+	ret = enable_controllers("/cg/cg/cg", "memory");
+	if (!ASSERT_OK(ret, "enable_controllers"))
+		goto cleanup;
+
+	skel = memcg_ops__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "memcg_ops__open_and_load"))
+		goto cleanup;
+
+	map = bpf_object__find_map_by_name(skel->obj, "low_mcg_ops");
+	if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name low_mcg_ops"))
+		goto cleanup;
+
+	opts.relative_fd = first;
+	opts.flags = BPF_F_ALLOW_OVERRIDE;
+	link1 = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link1, "bpf_map__attach_struct_ops_opts"))
+		goto cleanup;
+
+	opts.relative_fd = second;
+	opts.flags = 0;
+	link2 = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_OK_PTR(link2, "bpf_map__attach_struct_ops_opts"))
+		goto cleanup;
+
+	opts.relative_fd = third;
+	opts.flags = 0;
+	link3 = bpf_map__attach_struct_ops_opts(map, &opts);
+	if (!ASSERT_ERR_PTR(link3, "bpf_map__attach_struct_ops_opts"))
+		goto cleanup;
+
+cleanup:
+	bpf_link__destroy(link1);
+	bpf_link__destroy(link2);
+	bpf_link__destroy(link3);
+	memcg_ops__detach(skel);
+	close(first);
+	close(second);
+	close(third);
+	cleanup_cgroup_environment();
+}
-- 
2.43.0

[RFC PATCH bpf-next v4 12/12] samples/bpf: Add memcg priority control example

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

Add a sample program to demonstrate a practical use case for the
`memcg_bpf_ops` feature: priority-based memory throttling.

The sample consists of a BPF program and a userspace loader:

1. memcg.bpf.c: A BPF program that monitors PGFAULT events on a
   high-priority cgroup. When activity exceeds a threshold, it uses
   the `get_high_delay_ms`, `below_low`, or `below_min` hooks to
   apply pressure on a low-priority cgroup.

2. memcg.c: A userspace loader that configures and attaches the BPF
   program. It takes command-line arguments for the high and low
   priority cgroup paths, a pressure threshold, and the desired
   throttling delay (`over_high_ms`).

This provides a clear, working example of how to implement a dynamic,
priority-aware memory management policy. A user can create two
cgroups, run workloads of different priorities, and observe the
low-priority workload being throttled to protect the high-priority one.

Example usage:
  # ./memcg --low_path /sys/fs/cgroup/low \
  #         --high_path /sys/fs/cgroup/high \
  #         --threshold 100 --over_high_ms 1024

Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 MAINTAINERS             |   2 +
 samples/bpf/.gitignore  |   1 +
 samples/bpf/Makefile    |   8 +-
 samples/bpf/memcg.bpf.c | 129 ++++++++++++++++
 samples/bpf/memcg.c     | 327 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 466 insertions(+), 1 deletion(-)
 create mode 100644 samples/bpf/memcg.bpf.c
 create mode 100644 samples/bpf/memcg.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 7e07bb330eae..819ef271e011 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6470,6 +6470,8 @@ F:	mm/memcontrol-v1.c
 F:	mm/memcontrol-v1.h
 F:	mm/page_counter.c
 F:	mm/swap_cgroup.c
+F:	samples/bpf/memcg.bpf.c
+F:	samples/bpf/memcg.c
 F:	samples/cgroup/*
 F:	tools/testing/selftests/bpf/prog_tests/memcg_ops.c
 F:	tools/testing/selftests/bpf/progs/memcg_ops.c
diff --git a/samples/bpf/.gitignore b/samples/bpf/.gitignore
index 0002cd359fb1..0de6569cdefd 100644
--- a/samples/bpf/.gitignore
+++ b/samples/bpf/.gitignore
@@ -49,3 +49,4 @@ iperf.*
 /vmlinux.h
 /bpftool/
 /libbpf/
+memcg
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 95a4fa1f1e44..b00698bdc53b 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -37,6 +37,7 @@ tprogs-y += xdp_fwd
 tprogs-y += task_fd_query
 tprogs-y += ibumad
 tprogs-y += hbm
+tprogs-y += memcg
 
 # Libbpf dependencies
 LIBBPF_SRC = $(TOOLS_PATH)/lib/bpf
@@ -122,6 +123,7 @@ always-y += task_fd_query_kern.o
 always-y += ibumad_kern.o
 always-y += hbm_out_kern.o
 always-y += hbm_edt_kern.o
+always-y += memcg.bpf.o
 
 COMMON_CFLAGS = $(TPROGS_USER_CFLAGS)
 TPROGS_LDFLAGS = $(TPROGS_USER_LDFLAGS)
@@ -289,6 +291,8 @@ $(obj)/hbm_out_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
 $(obj)/hbm.o: $(src)/hbm.h
 $(obj)/hbm_edt_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
 
+memcg: $(obj)/memcg.skel.h
+
 # Override includes for xdp_sample_user.o because $(srctree)/usr/include in
 # TPROGS_CFLAGS causes conflicts
 XDP_SAMPLE_CFLAGS += -Wall -O2 \
@@ -347,11 +351,13 @@ $(obj)/%.bpf.o: $(src)/%.bpf.c $(obj)/vmlinux.h $(src)/xdp_sample.bpf.h $(src)/x
 		-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
 		-c $(filter %.bpf.c,$^) -o $@
 
-LINKED_SKELS := xdp_router_ipv4.skel.h
+LINKED_SKELS := xdp_router_ipv4.skel.h memcg.skel.h
 clean-files += $(LINKED_SKELS)
 
 xdp_router_ipv4.skel.h-deps := xdp_router_ipv4.bpf.o xdp_sample.bpf.o
 
+memcg.skel.h-deps := memcg.bpf.o
+
 LINKED_BPF_SRCS := $(patsubst %.bpf.o,%.bpf.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
 
 BPF_SRCS_LINKED := $(notdir $(wildcard $(src)/*.bpf.c))
diff --git a/samples/bpf/memcg.bpf.c b/samples/bpf/memcg.bpf.c
new file mode 100644
index 000000000000..44087a206a61
--- /dev/null
+++ b/samples/bpf/memcg.bpf.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#define ONE_SECOND_NS	1000000000
+
+struct local_config {
+	u64 threshold;
+	u64 high_cgroup_id;
+	bool use_below_low;
+	bool use_below_min;
+	unsigned int over_high_ms;
+} local_config;
+
+struct AggregationData {
+	u64 sum;
+	u64 window_start_ts;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct AggregationData);
+} aggregation_map SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, u64);
+} trigger_ts_map SEC(".maps");
+
+SEC("tp/memcg/count_memcg_events")
+int
+handle_count_memcg_events(struct trace_event_raw_memcg_rstat_events *ctx)
+{
+	u32 key = 0;
+	struct AggregationData *data;
+	u64 current_ts;
+
+	if (ctx->id != local_config.high_cgroup_id ||
+	    (ctx->item != PGFAULT))
+		goto out;
+
+	data = bpf_map_lookup_elem(&aggregation_map, &key);
+	if (!data)
+		goto out;
+
+	current_ts = bpf_ktime_get_ns();
+
+	if (current_ts - data->window_start_ts < ONE_SECOND_NS) {
+		data->sum += ctx->val;
+	} else {
+		data->window_start_ts = current_ts;
+		data->sum = ctx->val;
+	}
+
+	if (data->sum > local_config.threshold) {
+		bpf_map_update_elem(&trigger_ts_map, &key, &current_ts,
+				    BPF_ANY);
+		data->sum = 0;
+		data->window_start_ts = current_ts;
+	}
+
+out:
+	return 0;
+}
+
+static bool need_threshold(void)
+{
+	u32 key = 0;
+	u64 *trigger_ts;
+	bool ret = false;
+
+	trigger_ts = bpf_map_lookup_elem(&trigger_ts_map, &key);
+	if (!trigger_ts || *trigger_ts == 0)
+		goto out;
+
+	u64 current_ts = bpf_ktime_get_ns();
+
+	if (current_ts - *trigger_ts < ONE_SECOND_NS)
+		ret = true;
+
+out:
+	return ret;
+}
+
+SEC("struct_ops/below_low")
+unsigned int below_low_impl(struct mem_cgroup *memcg)
+{
+	if (!local_config.use_below_low)
+		return false;
+
+	return need_threshold();
+}
+
+SEC("struct_ops/below_min")
+unsigned int below_min_impl(struct mem_cgroup *memcg)
+{
+	if (!local_config.use_below_min)
+		return false;
+
+	return need_threshold();
+}
+
+SEC("struct_ops/get_high_delay_ms")
+unsigned int get_high_delay_ms_impl(struct mem_cgroup *memcg)
+{
+	if (local_config.over_high_ms && need_threshold())
+		return local_config.over_high_ms;
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct memcg_bpf_ops high_mcg_ops = {
+	.below_low = (void *)below_low_impl,
+	.below_min = (void *)below_min_impl,
+};
+
+SEC(".struct_ops.link")
+struct memcg_bpf_ops low_mcg_ops = {
+	.get_high_delay_ms = (void *)get_high_delay_ms_impl,
+};
+
+char LICENSE[] SEC("license") = "GPL";
diff --git a/samples/bpf/memcg.c b/samples/bpf/memcg.c
new file mode 100644
index 000000000000..6d59a722f581
--- /dev/null
+++ b/samples/bpf/memcg.c
@@ -0,0 +1,327 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <getopt.h>
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+
+#ifndef __MEMCG_RSTAT_SIMPLE_BPF_SKEL_H__
+#define u64 uint64_t
+#endif
+
+struct local_config {
+	u64 threshold;
+	u64 high_cgroup_id;
+	bool use_below_low;
+	bool use_below_min;
+	unsigned int over_high_ms;
+} local_config;
+
+#include "memcg.skel.h"
+
+static bool exiting;
+
+static void sig_handler(int sig)
+{
+	exiting = true;
+}
+
+static void usage(char *name)
+{
+	fprintf(stderr,
+		"Usage: %s --low_path=<path> --high_path=<path> \\\n"
+		"          --threshold=<value> [OPTIONS]\n\n",
+		name);
+	fprintf(stderr, "Required arguments:\n");
+	fprintf(stderr,
+		"  -l, --low_path=PATH    Low priority memcgroup path\n");
+	fprintf(stderr,
+		"  -g, --high_path=PATH   High priority memcgroup path\n");
+	fprintf(stderr,
+		"  -t, --threshold=VALUE  The sum of 'val' PGSCAN of\n");
+	fprintf(stderr,
+		"                         high priority memcgroup in\n");
+	fprintf(stderr,
+		"                         1 sec to trigger low priority\n");
+	fprintf(stderr,
+		"                         cgroup over_high\n\n");
+	fprintf(stderr, "Optional arguments:\n");
+	fprintf(stderr, "  -o, --over_high_ms=VALUE\n");
+	fprintf(stderr,
+		"                         Low_path over_high_ms value\n");
+	fprintf(stderr,
+		"                         (default: 0)\n");
+	fprintf(stderr, "  -L, --use_below_low    Enable use_below_low flag\n");
+	fprintf(stderr, "  -M, --use_below_min    Enable use_below_min flag\n");
+	fprintf(stderr,
+		"  -O, --allow_override   Enable BPF_F_ALLOW_OVERRIDE\n");
+	fprintf(stderr,
+		"                         flag\n");
+	fprintf(stderr, "  -h, --help             Show this help message\n\n");
+	fprintf(stderr, "Examples:\n");
+	fprintf(stderr, "  # Using long options:\n");
+	fprintf(stderr, "  %s --low_path=/sys/fs/cgroup/low \\\n", name);
+	fprintf(stderr, "     --high_path=/sys/fs/cgroup/high \\\n");
+	fprintf(stderr, "     --threshold=1000 --over_high_ms=500 \\\n"
+			"     --use_below_low\n\n");
+	fprintf(stderr, "  # Using short options:\n");
+	fprintf(stderr, "  %s -l /sys/fs/cgroup/low \\\n"
+			"     -g /sys/fs/cgroup/high \\\n",
+		name);
+	fprintf(stderr, "     -t 1000 -o 500 -L -M\n");
+}
+
+static uint64_t get_cgroup_id(const char *cgroup_path)
+{
+	struct stat st;
+
+	if (cgroup_path == NULL) {
+		fprintf(stderr, "Error: cgroup_path is NULL\n");
+		return 0;
+	}
+
+	if (stat(cgroup_path, &st) < 0) {
+		fprintf(stderr, "Error: stat(%s) failed: %d\n",
+			cgroup_path, errno);
+		return 0;
+	}
+
+	return (uint64_t)st.st_ino;
+}
+
+int main(int argc, char **argv)
+{
+	int low_cgroup_fd = -1, high_cgroup_fd = -1;
+	uint64_t threshold = 0, high_cgroup_id;
+	unsigned int over_high_ms = 0;
+	bool use_below_low = false, use_below_min = false;
+	__u32 opts_flags = 0;
+	const char *low_path = NULL;
+	const char *high_path = NULL;
+	const char *bpf_obj_file = "memcg.bpf.o";
+	struct bpf_object *obj = NULL;
+	struct bpf_program *prog = NULL;
+	struct bpf_link *link = NULL, *link_low = NULL, *link_high = NULL;
+	struct bpf_map *map;
+	struct memcg__bss *bss_data;
+	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
+	int err = -EINVAL;
+	int map_fd;
+	int opt;
+	int option_index = 0;
+
+	static struct option long_options[] = {
+		{"low_path",       required_argument, 0, 'l'},
+		{"high_path",      required_argument, 0, 'g'},
+		{"threshold",      required_argument, 0, 't'},
+		{"over_high_ms",   required_argument, 0, 'o'},
+		{"use_below_low",  no_argument,       0, 'L'},
+		{"use_below_min",  no_argument,       0, 'M'},
+		{"allow_override", no_argument,       0, 'O'},
+		{"help",           no_argument,       0, 'h'},
+		{0,                0,                 0,  0 }
+	};
+
+	while ((opt = getopt_long(argc, argv, "l:g:t:o:LMOh",
+				  long_options, &option_index)) != -1) {
+		switch (opt) {
+		case 'l':
+			low_path = optarg;
+			break;
+		case 'g':
+			high_path = optarg;
+			break;
+		case 't':
+			threshold = strtoull(optarg, NULL, 10);
+			break;
+		case 'o':
+			over_high_ms = strtoull(optarg, NULL, 10);
+			break;
+		case 'L':
+			use_below_low = true;
+			break;
+		case 'M':
+			use_below_min = true;
+			break;
+		case 'O':
+			opts_flags = BPF_F_ALLOW_OVERRIDE;
+			break;
+		case 'h':
+			usage(argv[0]);
+			return 0;
+		default:
+			usage(argv[0]);
+			return -EINVAL;
+		}
+	}
+
+	if (!low_path || !high_path || !threshold) {
+		fprintf(stderr,
+			"ERROR: Missing required arguments\n\n");
+		usage(argv[0]);
+		goto out;
+	}
+
+	low_cgroup_fd = open(low_path, O_RDONLY);
+	if (low_cgroup_fd < 0) {
+		fprintf(stderr,
+			"ERROR: open low cgroup '%s' failed: %d\n",
+			low_path, errno);
+		err = -errno;
+		goto out;
+	}
+
+	high_cgroup_id = get_cgroup_id(high_path);
+	if (!high_cgroup_id)
+		goto out;
+	high_cgroup_fd = open(high_path, O_RDONLY);
+	if (high_cgroup_fd < 0) {
+		fprintf(stderr,
+			"ERROR: open high cgroup '%s' failed: %d\n",
+			high_path, errno);
+		err = -errno;
+		goto out;
+	}
+
+	obj = bpf_object__open_file(bpf_obj_file, NULL);
+	err = libbpf_get_error(obj);
+	if (err) {
+		fprintf(stderr,
+			"ERROR: opening BPF object file '%s' failed: %d\n",
+			bpf_obj_file, err);
+		goto out;
+	}
+
+	map = bpf_object__find_map_by_name(obj, ".bss");
+	if (!map) {
+		fprintf(stderr, "ERROR: Failed to find .data map\n");
+		err = -ESRCH;
+		goto out;
+	}
+
+	err = bpf_object__load(obj);
+	if (err) {
+		fprintf(stderr,
+			"ERROR: loading BPF object file failed: %d\n",
+			err);
+		goto out;
+	}
+
+	map_fd = bpf_map__fd(map);
+	bss_data = malloc(bpf_map__value_size(map));
+	if (bss_data) {
+		__u32 key = 0;
+
+		memset(bss_data, 0, sizeof(struct local_config));
+		bss_data->local_config.high_cgroup_id = high_cgroup_id;
+		bss_data->local_config.threshold = threshold;
+		bss_data->local_config.over_high_ms = over_high_ms;
+		bss_data->local_config.use_below_low = use_below_low;
+		bss_data->local_config.use_below_min = use_below_min;
+
+		err = bpf_map_update_elem(map_fd, &key, bss_data, BPF_EXIST);
+		free(bss_data);
+		if (err) {
+			fprintf(stderr,
+				"ERROR: update config failed: %d\n",
+				err);
+			goto out;
+		}
+	} else {
+		fprintf(stderr,
+			"ERROR: allocate memory failed\n");
+		err = -ENOMEM;
+		goto out;
+	}
+
+	prog = bpf_object__find_program_by_name(obj,
+						"handle_count_memcg_events");
+	if (!prog) {
+		fprintf(stderr,
+			"ERROR: finding a prog in BPF object file failed\n");
+		goto out;
+	}
+
+	link = bpf_program__attach(prog);
+	err = libbpf_get_error(link);
+	if (err) {
+		fprintf(stderr,
+			"ERROR: bpf_program__attach failed: %d\n",
+			err);
+		goto out;
+	}
+
+	if (over_high_ms) {
+		map = bpf_object__find_map_by_name(obj, "low_mcg_ops");
+		if (!map) {
+			fprintf(stderr,
+				"ERROR: Failed to find low_mcg_ops map\n");
+			err = -ESRCH;
+			goto out;
+		}
+		LIBBPF_OPTS_RESET(opts,
+			.flags = opts_flags,
+			.relative_fd = low_cgroup_fd,
+		);
+		link_low = bpf_map__attach_struct_ops_opts(map, &opts);
+		if (!link_low) {
+			fprintf(stderr,
+				"Failed to attach struct ops low_mcg_ops: %d\n",
+				errno);
+			err = -errno;
+			goto out;
+		}
+	}
+
+	if (use_below_low || use_below_min) {
+		map = bpf_object__find_map_by_name(obj, "high_mcg_ops");
+		if (!map) {
+			fprintf(stderr,
+				"ERROR: Failed to find high_mcg_ops map\n");
+			err = -ESRCH;
+			goto out;
+		}
+		LIBBPF_OPTS_RESET(opts,
+			.flags = opts_flags,
+			.relative_fd = high_cgroup_fd,
+		);
+		link_high = bpf_map__attach_struct_ops_opts(map, &opts);
+		if (!link_high) {
+			fprintf(stderr,
+				"Failed to attach struct ops high_mcg_ops: %d\n",
+				errno);
+			err = -errno;
+			goto out;
+		}
+	}
+
+	printf("Successfully attached!\n");
+
+	signal(SIGINT, sig_handler);
+	signal(SIGTERM, sig_handler);
+
+	while (!exiting)
+		pause();
+
+	printf("Exiting...\n");
+
+out:
+	bpf_link__destroy(link);
+	bpf_link__destroy(link_low);
+	bpf_link__destroy(link_high);
+	bpf_object__close(obj);
+	close(low_cgroup_fd);
+	close(high_cgroup_fd);
+	return err;
+}
-- 
2.43.0

Re: [RFC PATCH bpf-next v4 11/12] selftests/bpf: Add test for memcg_bpf_ops hierarchies

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1867 bytes --]

> diff --git a/tools/testing/selftests/bpf/prog_tests/memcg_ops.c b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
> index a019ba2387bc..08ac97752ac9 100644
> --- a/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
> +++ b/tools/testing/selftests/bpf/prog_tests/memcg_ops.c
> @@ -539,3 +539,73 @@ void test_memcg_ops_below_min_over_high(void)

[ ... ]

> +void test_memcg_ops_hierarchies(void)
> +{
> +	int ret, first = -1, second = -1, third = -1;
> +	struct memcg_ops *skel;
                          ^^^^

Should skel be initialized to NULL here? The other tests in this file
(test_memcg_ops_over_high, test_memcg_ops_below_low_over_high, and
test_memcg_ops_below_min_over_high) all initialize their skeleton pointers
to NULL.

If any of the early checks fail (e.g. setup_cgroup_environment() or
create_and_get_cgroup()), the code jumps to cleanup where memcg_ops__detach()
is called. The skeleton __detach() function dereferences its argument without
checking for NULL, which would cause a crash with an uninitialized pointer.

> +	struct bpf_map *map;
> +	struct bpf_link *link1 = NULL, *link2 = NULL, *link3 = NULL;
> +	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
> +
> +	ret = setup_cgroup_environment();
> +	if (!ASSERT_OK(ret, "setup_cgroup_environment"))
> +		goto cleanup;

[ ... ]

> +cleanup:
> +	bpf_link__destroy(link1);
> +	bpf_link__destroy(link2);
> +	bpf_link__destroy(link3);
> +	memcg_ops__detach(skel);
                         ^^^^

This dereferences skel without checking if it was ever assigned.

> +	close(first);
> +	close(second);
> +	close(third);
> +	cleanup_cgroup_environment();
> +}


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21352241149

Re: [RFC PATCH bpf-next v4 08/12] mm: memcontrol: Add BPF struct_ops for memory controller

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 3192 bytes --]

> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index f3b8c71870d8..1083be5d0362 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h

[ ... ]

> +#else /* CONFIG_BPF_SYSCALL */
> +
> +static inline unsigned long
> +bpf_memcg_get_high_delay(struct mem_cgroup *memcg) { return 0; }
> +static inline bpf_memcg_below_low(struct mem_cgroup *memcg) { return false; }
> +static inline bpf_memcg_below_min(struct mem_cgroup *memcg) { return false; }
                ^^^^^^^^^^^^^^^^^^^^

These two stubs are missing the bool return type. This will cause a
compilation error when CONFIG_BPF_SYSCALL is not set. Should these be:

  static inline bool bpf_memcg_below_low(...)
  static inline bool bpf_memcg_below_min(...)

> +static inline void memcontrol_bpf_online(struct mem_cgroup *memcg) { }
> +static inline void memcontrol_bpf_offline(struct mem_cgroup *memcg) { }
> +
> +#endif /* CONFIG_BPF_SYSCALL */

[ ... ]

> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
> index 716df49d7647..20c5c3552ce3 100644
> --- a/mm/bpf_memcontrol.c
> +++ b/mm/bpf_memcontrol.c

[ ... ]

> +static int bpf_memcg_ops_reg(void *kdata, struct bpf_link *link)
> +{
> +	struct bpf_struct_ops_link *ops_link
> +		= container_of(link, struct bpf_struct_ops_link, link);
> +	struct memcg_bpf_ops *ops = kdata;
> +	struct mem_cgroup *memcg, *iter = NULL;
> +	int err = 0;
> +
> +	memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id);
> +	if (IS_ERR_OR_NULL(memcg))
> +		return PTR_ERR(memcg);
> +
> +	cgroup_lock();
> +	while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
> +		if (READ_ONCE(iter->bpf_ops)) {
> +			mem_cgroup_iter_break(memcg, iter);
> +			err = -EBUSY;
> +			break;
> +		}
> +		WRITE_ONCE(iter->bpf_ops, ops);
> +	}
> +	if (err)
> +		clean_memcg_bpf_ops(memcg, NULL);
                                      ^^^^

When registration fails because a descendant cgroup already has a BPF
program attached, this calls clean_memcg_bpf_ops() with NULL. Looking at
clean_memcg_bpf_ops():

  while ((iter = mem_cgroup_iter(memcg, iter, NULL))) {
      if (ops) {
          if (!WARN_ON(READ_ONCE(iter->bpf_ops) != ops))
              WRITE_ONCE(iter->bpf_ops, NULL);
      } else
          WRITE_ONCE(iter->bpf_ops, NULL);   // unconditional clear
  }

With ops=NULL, this will unconditionally clear bpf_ops for all
descendants in the hierarchy, including the cgroup that already had a
different BPF program attached (which caused the -EBUSY error). This
would incorrectly detach that existing program.

Should this be clean_memcg_bpf_ops(memcg, ops) instead, so it only clears
the ops that were written during this failed registration attempt?

Note: This issue appears to be addressed in the subsequent commit
5f3bb9a8c33f ("mm/bpf: Add BPF_F_ALLOW_OVERRIDE support for
memcg_bpf_ops") which completely rewrites the registration logic.

> +	cgroup_unlock();
> +
> +	mem_cgroup_put(memcg);
> +	return err;
> +}


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21352241149