* [RFC PATCH 1/3] mm/lru_gen: refactor to extract helper functions
2026-01-21 12:39 [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Jiayuan Chen
@ 2026-01-21 12:39 ` Jiayuan Chen
2026-01-21 12:39 ` [RFC PATCH 2/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Jiayuan Chen
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Jiayuan Chen @ 2026-01-21 12:39 UTC (permalink / raw)
To: linux-mm
Cc: Jiayuan Chen, Tejun Heo, Johannes Weiner, Michal Koutný,
Jonathan Corbet, Andrew Morton, David Hildenbrand,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Roman Gushchin, Shakeel Butt, Muchun Song, Qi Zheng,
cgroups, linux-doc, linux-kernel
From: Jiayuan Chen <jiayuan.chen@shopee.com>
Extract helper functions from debugfs interface for code reuse:
- lru_gen_print_lruvec(): Print generations for a single lruvec,
extracted from lru_gen_seq_show().
- __run_cmd(): Core command execution logic, extracted from run_cmd().
These helpers will be used by the upcoming memcg interface.
No functional change.
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
---
mm/vmscan.c | 82 +++++++++++++++++++++++++++++++----------------------
1 file changed, 48 insertions(+), 34 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 619691aa4393..8ea5b67daa36 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5397,29 +5397,13 @@ static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
seq_putc(m, '\n');
}
-/* see Documentation/admin-guide/mm/multigen_lru.rst for details */
-static int lru_gen_seq_show(struct seq_file *m, void *v)
+/* Print generations for a single lruvec - helper for debugfs and memcg */
+static void lru_gen_print_lruvec(struct seq_file *m, struct lruvec *lruvec,
+ unsigned long max_seq, unsigned long *min_seq,
+ bool full)
{
unsigned long seq;
- bool full = debugfs_get_aux_num(m->file);
- struct lruvec *lruvec = v;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
- int nid = lruvec_pgdat(lruvec)->node_id;
- struct mem_cgroup *memcg = lruvec_memcg(lruvec);
- DEFINE_MAX_SEQ(lruvec);
- DEFINE_MIN_SEQ(lruvec);
-
- if (nid == first_memory_node) {
- const char *path = memcg ? m->private : "";
-
-#ifdef CONFIG_MEMCG
- if (memcg)
- cgroup_path(memcg->css.cgroup, m->private, PATH_MAX);
-#endif
- seq_printf(m, "memcg %5hu %s\n", mem_cgroup_id(memcg), path);
- }
-
- seq_printf(m, " node %5d\n", nid);
if (!full)
seq = evictable_min_seq(min_seq, MAX_SWAPPINESS / 2);
@@ -5431,7 +5415,7 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
for (; seq <= max_seq; seq++) {
int type, zone;
int gen = lru_gen_from_seq(seq);
- unsigned long birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
+ unsigned long birth = READ_ONCE(lrugen->timestamps[gen]);
seq_printf(m, " %10lu %10u", seq, jiffies_to_msecs(jiffies - birth));
@@ -5450,7 +5434,31 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
if (full)
lru_gen_seq_show_full(m, lruvec, max_seq, min_seq, seq);
}
+}
+
+/* see Documentation/admin-guide/mm/multigen_lru.rst for details */
+static int lru_gen_seq_show(struct seq_file *m, void *v)
+{
+ bool full = debugfs_get_aux_num(m->file);
+ struct lruvec *lruvec = v;
+ int nid = lruvec_pgdat(lruvec)->node_id;
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+ DEFINE_MAX_SEQ(lruvec);
+ DEFINE_MIN_SEQ(lruvec);
+
+ if (nid == first_memory_node) {
+ const char *path = memcg ? m->private : "";
+
+#ifdef CONFIG_MEMCG
+ if (memcg)
+ cgroup_path(memcg->css.cgroup, m->private, PATH_MAX);
+#endif
+ seq_printf(m, "memcg %5hu %s\n", mem_cgroup_id(memcg), path);
+ }
+ seq_printf(m, " node %5d\n", nid);
+
+ lru_gen_print_lruvec(m, lruvec, max_seq, min_seq, full);
return 0;
}
@@ -5501,6 +5509,24 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
return -EINTR;
}
+/* Core command execution - helper for debugfs and memcg */
+static int __run_cmd(char cmd, struct lruvec *lruvec, unsigned long seq,
+ struct scan_control *sc, int swappiness, unsigned long opt)
+{
+ if (swappiness < MIN_SWAPPINESS)
+ swappiness = get_swappiness(lruvec, sc);
+ else if (swappiness > SWAPPINESS_ANON_ONLY)
+ return -EINVAL;
+
+ switch (cmd) {
+ case '+':
+ return run_aging(lruvec, seq, swappiness, opt);
+ case '-':
+ return run_eviction(lruvec, seq, sc, swappiness, opt);
+ }
+ return -EINVAL;
+}
+
static int run_cmd(char cmd, int memcg_id, int nid, unsigned long seq,
struct scan_control *sc, int swappiness, unsigned long opt)
{
@@ -5530,19 +5556,7 @@ static int run_cmd(char cmd, int memcg_id, int nid, unsigned long seq,
sc->target_mem_cgroup = memcg;
lruvec = get_lruvec(memcg, nid);
- if (swappiness < MIN_SWAPPINESS)
- swappiness = get_swappiness(lruvec, sc);
- else if (swappiness > SWAPPINESS_ANON_ONLY)
- goto done;
-
- switch (cmd) {
- case '+':
- err = run_aging(lruvec, seq, swappiness, opt);
- break;
- case '-':
- err = run_eviction(lruvec, seq, sc, swappiness, opt);
- break;
- }
+ err = __run_cmd(cmd, lruvec, seq, sc, swappiness, opt);
done:
mem_cgroup_put(memcg);
--
2.43.0
^ permalink raw reply [flat|nested] 6+ messages in thread* [RFC PATCH 2/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2
2026-01-21 12:39 [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Jiayuan Chen
2026-01-21 12:39 ` [RFC PATCH 1/3] mm/lru_gen: refactor to extract helper functions Jiayuan Chen
@ 2026-01-21 12:39 ` Jiayuan Chen
2026-01-21 12:39 ` [RFC PATCH 3/3] docs/cgroup: document memory.lru_gen interface Jiayuan Chen
2026-01-21 22:19 ` [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Shakeel Butt
3 siblings, 0 replies; 6+ messages in thread
From: Jiayuan Chen @ 2026-01-21 12:39 UTC (permalink / raw)
To: linux-mm
Cc: Jiayuan Chen, Tejun Heo, Johannes Weiner, Michal Koutný,
Jonathan Corbet, Andrew Morton, David Hildenbrand,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Roman Gushchin, Shakeel Butt, Muchun Song, Qi Zheng,
cgroups, linux-doc, linux-kernel
From: Jiayuan Chen <jiayuan.chen@shopee.com>
Add a memory.lru_gen interface to cgroup v2 that allows users to
interact with MGLRU directly on a specific cgroup without needing
to know the internal memcg_id.
Read (cat memory.lru_gen):
Display lru_gen information for this memcg across all NUMA nodes.
Write (echo to memory.lru_gen):
Execute aging or eviction commands.
Format: cmd nid seq [swappiness] [opt]
cmd: '+' for aging, '-' for eviction
nid: node id
seq: generation sequence number
swappiness: optional, or 'max' for anonymous memory only
opt: force_scan for aging, nr_to_reclaim for eviction
Example:
# Show lru_gen info
cat /sys/fs/cgroup/mygroup/memory.lru_gen
# Run aging on node 0 with seq 100
echo '+ 0 100' > /sys/fs/cgroup/mygroup/memory.lru_gen
# Run eviction on node 0 with seq 99, swappiness 50, reclaim 1000 pages
echo '- 0 99 50 1000' > /sys/fs/cgroup/mygroup/memory.lru_gen
Test result:
cgcreate -g memory:test_group
// create 1GB page cache, loop access 200MB as hot pages.
cgexec -g memory:test_group ./cache_sim &
cat /sys/fs/cgroup/test_group/memory.lru_gen
node 0 (min_seq=0/0, max_seq=3)
0 48744 0 4
1 48744 0 0
2 48744 24 262144
3 48744 0 0
node 1 (min_seq=0/0, max_seq=3)
0 48744 0 0
1 48744 0 0
2 48744 1 0
3 48744 0 0
// age
echo '+ 0 3' > /sys/fs/cgroup/test_group/memory.lru_gen
cat /sys/fs/cgroup/test_group/memory.lru_gen
memcg 35 /test_group
node 0 (min_seq=1/1, max_seq=4)
1 216564 0 3
2 216564 24 262144
3 216564 0 1
4 14936 0 0
node 1 (min_seq=0/0, max_seq=3)
0 216564 0 0
1 216564 0 0
2 216564 1 0
3 216564 0 0
// age
echo '+ 0 4' > /sys/fs/cgroup/test_group/memory.lru_gen
cat /sys/fs/cgroup/test_group/memory.lru_gen
memcg 35 /test_group
node 0 (min_seq=2/2, max_seq=5)
2 266880 23 210947
3 266880 0 1
4 65252 1 51200
5 9320 0 0
node 1 (min_seq=0/0, max_seq=3)
0 266880 0 0
1 266880 0 0
2 266880 1 0
3 266880 0 0
// age
echo '+ 0 5' > /sys/fs/cgroup/test_group/memory.lru_gen
node 0 (min_seq=3/3, max_seq=6)
3 318384 0 210948
4 116756 0 0
5 60824 1 51200
6 3408 23 0
node 1 (min_seq=0/0, max_seq=3)
0 318384 0 0
1 318384 0 0
2 318384 1 0
3 318384 0 0
// reclaim 200000 pages
echo '- 0 3 0 200000' > /sys/fs/cgroup/test_group/memory.lru_gen
cat /sys/fs/cgroup/test_group/memory.lru_gen
node 0 (min_seq=3/3, max_seq=6)
3 760308 0 10884
4 558680 0 0
5 502748 1 51200
6 445332 23 0
node 1 (min_seq=0/0, max_seq=3)
0 760308 0 0
1 760308 0 0
2 760308 1 0
3 760308 0 0
// reclaim 20000 pages
echo '- 0 3 0 20000' > /sys/fs/cgroup/test_group/memory.lru_gen
cat /sys/fs/cgroup/test_group/memory.lru_gen
node 0 (min_seq=3/5, max_seq=6)
3 826864 0 0
4 625236 0 0
5 569304 1 51201
6 511888 23 0
node 1 (min_seq=0/0, max_seq=3)
0 826864 0 0
1 826864 0 0
2 826864 1 0
3 826864 0 0
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
---
include/linux/mmzone.h | 16 +++++++
mm/memcontrol.c | 31 ++++++++++++++
mm/vmscan.c | 94 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 141 insertions(+)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fc5d6c88d2f0..8edb9549b435 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -625,6 +625,11 @@ void lru_gen_offline_memcg(struct mem_cgroup *memcg);
void lru_gen_release_memcg(struct mem_cgroup *memcg);
void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid);
+/* memcg interface */
+struct seq_file;
+void lru_gen_seq_show_memcg(struct seq_file *m, struct mem_cgroup *memcg);
+int lru_gen_seq_write_memcg(struct mem_cgroup *memcg, char *buf);
+
#else /* !CONFIG_LRU_GEN */
static inline void lru_gen_init_pgdat(struct pglist_data *pgdat)
@@ -664,6 +669,17 @@ static inline void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid)
{
}
+struct seq_file;
+static inline void lru_gen_seq_show_memcg(struct seq_file *m,
+ struct mem_cgroup *memcg)
+{
+}
+
+static inline int lru_gen_seq_write_memcg(struct mem_cgroup *memcg, char *buf)
+{
+ return -EOPNOTSUPP;
+}
+
#endif /* CONFIG_LRU_GEN */
struct lruvec {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 75fc22a33b28..e2f13a69b891 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4565,6 +4565,30 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
return nbytes;
}
+#ifdef CONFIG_LRU_GEN
+static int memory_lru_gen_show(struct seq_file *m, void *v)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
+
+ lru_gen_seq_show_memcg(m, memcg);
+ return 0;
+}
+
+static ssize_t memory_lru_gen_write(struct kernfs_open_file *of, char *buf,
+ size_t nbytes, loff_t off)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+ int ret;
+
+ buf = strstrip(buf);
+ ret = lru_gen_seq_write_memcg(memcg, buf);
+ if (ret)
+ return ret;
+
+ return nbytes;
+}
+#endif
+
static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off)
{
@@ -4649,6 +4673,13 @@ static struct cftype memory_files[] = {
.flags = CFTYPE_NS_DELEGATABLE,
.write = memory_reclaim,
},
+#ifdef CONFIG_LRU_GEN
+ {
+ .name = "lru_gen",
+ .seq_show = memory_lru_gen_show,
+ .write = memory_lru_gen_write,
+ },
+#endif
{ } /* terminate */
};
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8ea5b67daa36..43f38f9f43c5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5668,6 +5668,100 @@ static const struct file_operations lru_gen_ro_fops = {
.release = seq_release,
};
+/******************************************************************************
+ * memcg interface
+ ******************************************************************************/
+
+void lru_gen_seq_show_memcg(struct seq_file *m, struct mem_cgroup *memcg)
+{
+ int nid;
+ char *path;
+
+ path = kvmalloc(PATH_MAX, GFP_KERNEL);
+#ifdef CONFIG_MEMCG
+ if (memcg && path)
+ cgroup_path(memcg->css.cgroup, path, PATH_MAX);
+#endif
+ seq_printf(m, "memcg %5hu %s\n", mem_cgroup_id(memcg),
+ (memcg && path) ? path : "");
+ kvfree(path);
+
+ for_each_node_state(nid, N_MEMORY) {
+ struct lruvec *lruvec = get_lruvec(memcg, nid);
+ DEFINE_MAX_SEQ(lruvec);
+ DEFINE_MIN_SEQ(lruvec);
+
+ seq_printf(m, " node %5d (min_seq=%lu/%lu, max_seq=%lu)\n",
+ nid, min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE], max_seq);
+ lru_gen_print_lruvec(m, lruvec, max_seq, min_seq, false);
+ }
+}
+
+int lru_gen_seq_write_memcg(struct mem_cgroup *memcg, char *buf)
+{
+ char *cur, *next;
+ unsigned int flags;
+ struct blk_plug plug;
+ int err = -EINVAL;
+ struct scan_control sc = {
+ .may_writepage = true,
+ .may_unmap = true,
+ .may_swap = true,
+ .reclaim_idx = MAX_NR_ZONES - 1,
+ .gfp_mask = GFP_KERNEL,
+ .proactive = true,
+ .target_mem_cgroup = memcg,
+ };
+
+ set_task_reclaim_state(current, &sc.reclaim_state);
+ flags = memalloc_noreclaim_save();
+ blk_start_plug(&plug);
+ if (!set_mm_walk(NULL, true)) {
+ err = -ENOMEM;
+ goto done;
+ }
+
+ next = buf;
+ while ((cur = strsep(&next, ",;\n"))) {
+ int n, end;
+ char cmd, swap_str[5];
+ unsigned int nid, swappiness = -1;
+ unsigned long seq, opt = -1;
+ struct lruvec *lruvec;
+
+ cur = skip_spaces(cur);
+ if (!*cur)
+ continue;
+
+ n = sscanf(cur, "%c %u %lu %n %4s %n %lu %n", &cmd, &nid,
+ &seq, &end, swap_str, &end, &opt, &end);
+ if (n < 3 || cur[end]) {
+ err = -EINVAL;
+ break;
+ }
+ if (n > 3 && strcmp("max", swap_str) == 0)
+ swappiness = SWAPPINESS_ANON_ONLY;
+ else if (n > 3 && kstrtouint(swap_str, 0, &swappiness))
+ break;
+
+ if (nid >= MAX_NUMNODES || !node_state(nid, N_MEMORY)) {
+ err = -EINVAL;
+ break;
+ }
+
+ lruvec = get_lruvec(memcg, nid);
+ err = __run_cmd(cmd, lruvec, seq, &sc, swappiness, opt);
+ if (err)
+ break;
+ }
+done:
+ clear_mm_walk();
+ blk_finish_plug(&plug);
+ memalloc_noreclaim_restore(flags);
+ set_task_reclaim_state(current, NULL);
+ return err;
+}
+
/******************************************************************************
* initialization
******************************************************************************/
--
2.43.0
^ permalink raw reply [flat|nested] 6+ messages in thread* [RFC PATCH 3/3] docs/cgroup: document memory.lru_gen interface
2026-01-21 12:39 [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Jiayuan Chen
2026-01-21 12:39 ` [RFC PATCH 1/3] mm/lru_gen: refactor to extract helper functions Jiayuan Chen
2026-01-21 12:39 ` [RFC PATCH 2/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Jiayuan Chen
@ 2026-01-21 12:39 ` Jiayuan Chen
2026-01-21 22:19 ` [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Shakeel Butt
3 siblings, 0 replies; 6+ messages in thread
From: Jiayuan Chen @ 2026-01-21 12:39 UTC (permalink / raw)
To: linux-mm
Cc: Jiayuan Chen, Tejun Heo, Johannes Weiner, Michal Koutný,
Jonathan Corbet, Andrew Morton, Axel Rasmussen, Yuanchu Xie,
Wei Xu, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett,
Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko,
Roman Gushchin, Shakeel Butt, Muchun Song, Qi Zheng, cgroups,
linux-doc, linux-kernel
From: Jiayuan Chen <jiayuan.chen@shopee.com>
Add documentation for the memory.lru_gen interface in cgroup v2.
For detailed information about MGLRU and the command format, refer
to the multi-gen LRU documentation.
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
---
Documentation/admin-guide/cgroup-v2.rst | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 7f5b59d95fce..bb3ca7ffd600 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1426,6 +1426,23 @@ PAGE_SIZE multiple when read back.
This means that the networking layer will not adapt based on
reclaim induced by memory.reclaim.
+ memory.lru_gen
+ A read-write file that exists when CONFIG_LRU_GEN is enabled.
+
+ Reading this file displays the multi-gen LRU information for
+ this memcg, including generation numbers, page counts for
+ anonymous and file pages across all NUMA nodes.
+
+ Writing to this file allows performing aging or eviction
+ operations on this memcg. The format is::
+
+ echo '<cmd> <node_id> <seq> [<swappiness> [<opt>]]' > memory.lru_gen
+
+ This interface provides the same functionality as the debugfs
+ lru_gen interface but operates directly on the cgroup without
+ requiring the memcg_id. For detailed documentation of the
+ command format and MGLRU, see Documentation/admin-guide/mm/multigen_lru.rst.
+
The following nested keys are defined.
========== ================================
--
2.43.0
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2
2026-01-21 12:39 [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Jiayuan Chen
` (2 preceding siblings ...)
2026-01-21 12:39 ` [RFC PATCH 3/3] docs/cgroup: document memory.lru_gen interface Jiayuan Chen
@ 2026-01-21 22:19 ` Shakeel Butt
2026-01-22 1:30 ` Jiayuan Chen
3 siblings, 1 reply; 6+ messages in thread
From: Shakeel Butt @ 2026-01-21 22:19 UTC (permalink / raw)
To: Jiayuan Chen
Cc: linux-mm, Tejun Heo, Johannes Weiner, Michal Koutný,
Jonathan Corbet, Andrew Morton, Axel Rasmussen, Yuanchu Xie,
Wei Xu, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett,
Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko,
Roman Gushchin, Muchun Song, Qi Zheng, cgroups, linux-doc,
linux-kernel
On Wed, Jan 21, 2026 at 08:39:46PM +0800, Jiayuan Chen wrote:
> This patchset adds a memory.lru_gen interface to cgroup v2, allowing users
> to interact with MGLRU directly on a specific cgroup without needing to
> know the internal memcg_id.
Unfortunetely we don't want to expose reclaim implementation specific
interface to a cgroup.
>
> Motivation
> ==========
> Currently, the only way to perform aging or eviction on a specific memcg
> is through the debugfs interface (/sys/kernel/debug/lru_gen), which
> requires the memcg_id. However, there's no straightforward way to get the
> memcg_id for a given cgroup path. This makes it difficult for users to
> leverage MGLRU's proactive reclaim capabilities on specific cgroups.
From the next kernel version, this memcg_id will be inode number of the
cgroup for this interface. So, a simple 'ls -id cgroup_path' would be
sufficient for your use-case.
The relevant series [1] is in mm-tree at the moment and if you want, you
can backport it to your kernels.
[1] https://lkml.kernel.org/r/20251225232116.294540-1-shakeel.butt@linux.dev
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2
2026-01-21 22:19 ` [RFC PATCH 0/3] mm/lru_gen: add memory.lru_gen interface for cgroup v2 Shakeel Butt
@ 2026-01-22 1:30 ` Jiayuan Chen
0 siblings, 0 replies; 6+ messages in thread
From: Jiayuan Chen @ 2026-01-22 1:30 UTC (permalink / raw)
To: Shakeel Butt
Cc: linux-mm, Tejun Heo, Johannes Weiner, Michal Koutný,
Jonathan Corbet, Andrew Morton, Axel Rasmussen, Yuanchu Xie,
Wei Xu, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett,
Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko,
Roman Gushchin, Muchun Song, Qi Zheng, cgroups, linux-doc,
linux-kernel
January 22, 2026 at 06:19, "Shakeel Butt" <shakeel.butt@linux.dev mailto:shakeel.butt@linux.dev?to=%22Shakeel%20Butt%22%20%3Cshakeel.butt%40linux.dev%3E > wrote:
>
> On Wed, Jan 21, 2026 at 08:39:46PM +0800, Jiayuan Chen wrote:
>
> >
> > This patchset adds a memory.lru_gen interface to cgroup v2, allowing users
> > to interact with MGLRU directly on a specific cgroup without needing to
> > know the internal memcg_id.
> >
> Unfortunetely we don't want to expose reclaim implementation specific
> interface to a cgroup.
>
> >
> > Motivation
> > ==========
> > Currently, the only way to perform aging or eviction on a specific memcg
> > is through the debugfs interface (/sys/kernel/debug/lru_gen), which
> > requires the memcg_id. However, there's no straightforward way to get the
> > memcg_id for a given cgroup path. This makes it difficult for users to
> > leverage MGLRU's proactive reclaim capabilities on specific cgroups.
> >
> From the next kernel version, this memcg_id will be inode number of the
> cgroup for this interface. So, a simple 'ls -id cgroup_path' would be
> sufficient for your use-case.
>
> The relevant series [1] is in mm-tree at the moment and if you want, you
> can backport it to your kernels.
>
> [1] https://lkml.kernel.org/r/20251225232116.294540-1-shakeel.butt@linux.dev
>
Hi Shakeel,
Thanks for the review and the pointer to the inode-based memcg_id series.
I agree that using the cgroup inode number as memcg_id will simplify the
write operations (aging/eviction) through the debugfs interface.
However, I'd like to point out that the read operation (viewing lru_gen
info for a specific cgroup) is still not convenient. Currently, users
would need to parse the full debugfs output and grep for the specific
memcg_id, which can be cumbersome especially on systems with many cgroups.
Would it be acceptable to add a read-only command to /lru_gen that only displays
the lru_gen information for the specified cgroup?
Alternatively, if exposing any lru_gen info in cgroup is not desired, I
understand and will use the debugfs approach with scripting.
Thanks,
chenjiayuan
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