Signed-off-by: Jaewon Kim <redacted>
---
v2: move to /proc/meminfo_extra as a new file, meminfo_extra.c
    use rcu to reduce lock overhead
v1: print info at /proc/meminfo
---
 fs/proc/Makefile        |   1 +
 fs/proc/meminfo_extra.c | 123 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h      |   4 ++
 mm/page_alloc.c         |   1 +
 4 files changed, 129 insertions(+)
 create mode 100644 fs/proc/meminfo_extra.c

diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index bd08616ed8ba..83d2f55591c6 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile

@@ -19,6 +19,7 @@ proc-y	+= devices.o
 proc-y	+= interrupts.o
 proc-y	+= loadavg.o
 proc-y	+= meminfo.o
+proc-y	+= meminfo_extra.o
 proc-y	+= stat.o
 proc-y	+= uptime.o
 proc-y	+= util.o

diff --git a/fs/proc/meminfo_extra.c b/fs/proc/meminfo_extra.c
new file mode 100644
index 000000000000..bd3f0d2b7fb7
--- /dev/null
+++ b/fs/proc/meminfo_extra.c

@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/mm.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+
+static void show_val_kb(struct seq_file *m, const char *s, unsigned long num)
+{
+	seq_put_decimal_ull_width(m, s, num << (PAGE_SHIFT - 10), 8);
+	seq_write(m, " kB\n", 4);
+}
+
+static LIST_HEAD(meminfo_head);
+static DEFINE_SPINLOCK(meminfo_lock);
+
+#define NAME_SIZE      15
+#define NAME_BUF_SIZE  (NAME_SIZE + 2) /* ':' and '\0' */
+
+struct meminfo_extra {
+	struct list_head list;
+	atomic_long_t *val;
+	int shift_for_page;
+	char name[NAME_BUF_SIZE];
+	char name_pad[NAME_BUF_SIZE];
+};
+
+int register_meminfo_extra(atomic_long_t *val, int shift, const char *name)
+{
+	struct meminfo_extra *meminfo, *memtemp;
+	int len;
+	int error = 0;
+
+	meminfo = kzalloc(sizeof(*meminfo), GFP_KERNEL);
+	if (!meminfo) {
+		error = -ENOMEM;
+		goto out;
+	}
+
+	meminfo->val = val;
+	meminfo->shift_for_page = shift;
+	strncpy(meminfo->name, name, NAME_SIZE);
+	len = strlen(meminfo->name);
+	meminfo->name[len] = ':';
+	strncpy(meminfo->name_pad, meminfo->name, NAME_BUF_SIZE);
+	while (++len < NAME_BUF_SIZE - 1)
+		meminfo->name_pad[len] = ' ';
+
+	spin_lock(&meminfo_lock);
+	list_for_each_entry_rcu(memtemp, &meminfo_head, list) {
+		if (memtemp->val == val) {
+			error = -EINVAL;
+			break;
+		}
+	}
+	if (!error)
+		list_add_tail_rcu(&meminfo->list, &meminfo_head);
+	spin_unlock(&meminfo_lock);