From: xu xin <xu.xin16@zte.com.cn>

With the enablement of container-level KSM (e.g., via prctl), there is
a growing demand for container-level observability of KSM behavior.

The value of "ksm_rmap_items" indicates the total allocated ksm
rmap_items of this memcg, which could be used to determine how
unbeneficial the ksm-policy (like madvise), they are using brings,
since the bigger the ratio of ksm_rmap_items over ksm_merging_pages,
the more unbeneficial the ksm bring.

Add the counter in the existing memory.stat without adding a new interface.
We traverse all processes of a memcg and summing the processes'
ksm_rmap_items counters instead of adding enum item in memcg_stat_item
or node_stat_item and updating the corresponding enum counter when
ksmd manipulate pages.

Finally, we can look up ksm_rmap_items of per-memcg simply by:

    cat /sys/fs/cgroup/memory.stat | grep ksm_rmap_items

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
---
 include/linux/ksm.h |  1 +
 mm/ksm.c            | 38 ++++++++++++++++++++++++++++++++++++++
 mm/memcontrol.c     |  5 +++++
 3 files changed, 44 insertions(+)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 22e67ca7cba3..a41ed503f152 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -94,6 +94,7 @@ void collect_procs_ksm(const struct folio *folio, const struct page *page,
 		struct list_head *to_kill, int force_early);
 long ksm_process_profit(struct mm_struct *);
 bool ksm_process_mergeable(struct mm_struct *mm);
+void memcg_stat_ksm_show(struct mem_cgroup *memcg, struct seq_buf *s);

 #else  /* !CONFIG_KSM */

diff --git a/mm/ksm.c b/mm/ksm.c
index 2ef29802a49b..b533f0edaf96 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3308,6 +3308,44 @@ long ksm_process_profit(struct mm_struct *mm)
 }
 #endif /* CONFIG_PROC_FS */

+#ifdef CONFIG_MEMCG
+struct memcg_ksm_stat {
+	unsigned long ksm_rmap_items;
+};
+
+static int evaluate_memcg_ksm_stat(struct task_struct *task, void *arg)
+{
+	struct mm_struct *mm;
+	struct memcg_ksm_stat *ksm_stat = arg;
+
+	mm = get_task_mm(task);
+	if (mm) {
+		ksm_stat->ksm_rmap_items += mm->ksm_rmap_items;
+		mmput(mm);
+	}
+
+	return 0;
+}
+
+/* Show the ksm statistic count at memory.stat under cgroup mountpoint */
+void memcg_stat_ksm_show(struct mem_cgroup *memcg, struct seq_buf *s)
+{
+	struct memcg_ksm_stat ksm_stat;
+
+	if (mem_cgroup_is_root(memcg)) {
+		/* Just use the global counters when root memcg */
+		ksm_stat.ksm_rmap_items = ksm_rmap_items;
+	} else {
+		/* Initialization */
+		ksm_stat.ksm_rmap_items = 0;
+		/* Summing all processes'ksm statistic items */
+		mem_cgroup_scan_tasks(memcg, evaluate_memcg_ksm_stat, &ksm_stat);
+	}
+	/* Print memcg ksm statistic items */
+	seq_buf_printf(s, "ksm_rmap_items %lu\n", ksm_stat.ksm_rmap_items);
+}
+#endif
+
 #ifdef CONFIG_SYSFS
 /*
  * This all compiles without CONFIG_SYSFS, but is a waste of space.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 257d2c76b730..9595b132c6c3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -63,6 +63,7 @@
 #include <linux/seq_buf.h>
 #include <linux/sched/isolation.h>
 #include <linux/kmemleak.h>
+#include <linux/ksm.h>
 #include "internal.h"
 #include <net/sock.h>
 #include <net/ip.h>
@@ -1492,6 +1493,10 @@ static void memcg_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
 		}
 	}

+#ifdef CONFIG_KSM
+	memcg_stat_ksm_show(memcg, s);
+#endif
+
 	/* Accumulated memory events */
 	seq_buf_printf(s, "pgscan %lu\n",
 		       memcg_events(memcg, PGSCAN_KSWAPD) +
-- 
2.25.1

Hi,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on tj-cgroup/for-next linus/master v6.17-rc5 next-20250912]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/xu-xin16-zte-com-cn/memcg-add-per-memcg-ksm_rmap_items-stat/20250914-181132
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250914180351288rcLuZnPAMUej48nuTc7KV%40zte.com.cn
patch subject: [PATCH v2 1/5] memcg: add per-memcg ksm_rmap_items stat
config: parisc-randconfig-001-20250914 (https://download.01.org/0day-ci/archive/20250914/202509142147.WQI0impC-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250914/202509142147.WQI0impC-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509142147.WQI0impC-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/ksm.c: In function 'memcg_stat_ksm_show':
>> mm/ksm.c:3345:2: error: implicit declaration of function 'seq_buf_printf'; did you mean 'seq_bprintf'? [-Werror=implicit-function-declaration]
     seq_buf_printf(s, "ksm_rmap_items %lu\n", ksm_stat.ksm_rmap_items);
     ^~~~~~~~~~~~~~
     seq_bprintf
   cc1: some warnings being treated as errors


vim +3345 mm/ksm.c

  3329	
  3330	/* Show the ksm statistic count at memory.stat under cgroup mountpoint */
  3331	void memcg_stat_ksm_show(struct mem_cgroup *memcg, struct seq_buf *s)
  3332	{
  3333		struct memcg_ksm_stat ksm_stat;
  3334	
  3335		if (mem_cgroup_is_root(memcg)) {
  3336			/* Just use the global counters when root memcg */
  3337			ksm_stat.ksm_rmap_items = ksm_rmap_items;
  3338		} else {
  3339			/* Initialization */
  3340			ksm_stat.ksm_rmap_items = 0;
  3341			/* Summing all processes'ksm statistic items */
  3342			mem_cgroup_scan_tasks(memcg, evaluate_memcg_ksm_stat, &ksm_stat);
  3343		}
  3344		/* Print memcg ksm statistic items */
> 3345		seq_buf_printf(s, "ksm_rmap_items %lu\n", ksm_stat.ksm_rmap_items);
  3346	}
  3347	#endif
  3348	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki