[RFC PATCH v2 1/3] meminfo_extra: introduce meminfo extra

[Jaewon Kim <jaewon31.kim@samsung.com>]

Provide APIs to drivers so that they can show its memory usage on
/proc/meminfo_extra.

int register_meminfo_extra(atomic_long_t *val, int shift,
			   const char *name);
int unregister_meminfo_extra(atomic_long_t *val);

Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
---
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);
+	if (error)
+		kfree(meminfo);
+out:
+
+	return error;
+}
+EXPORT_SYMBOL(register_meminfo_extra);
+
+int unregister_meminfo_extra(atomic_long_t *val)
+{
+	struct meminfo_extra *memtemp;
+	int error = -EINVAL;
+
+	spin_lock(&meminfo_lock);
+	list_for_each_entry_rcu(memtemp, &meminfo_head, list) {
+		if (memtemp->val == val) {
+			list_del_rcu(&memtemp->list);
+			error = 0;
+			break;
+		}
+	}
+	spin_unlock(&meminfo_lock);
+	if (!error) {
+		synchronize_rcu();
+		kfree(memtemp);
+	}
+
+	return error;
+}
+EXPORT_SYMBOL(unregister_meminfo_extra);
+
+static void __meminfo_extra(struct seq_file *m)
+{
+	struct meminfo_extra *memtemp;
+	unsigned long nr_page;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(memtemp, &meminfo_head, list) {
+		nr_page = (unsigned long)atomic_long_read(memtemp->val);
+		nr_page = nr_page >> memtemp->shift_for_page;
+		if (m)
+			show_val_kb(m, memtemp->name_pad, nr_page);
+		else
+			pr_cont("%s%lukB ", memtemp->name, nr_page);
+	}
+	rcu_read_unlock();
+}
+
+void show_meminfo_extra(void)
+{
+	__meminfo_extra(NULL);
+}
+
+static int meminfo_extra_proc_show(struct seq_file *m, void *v)
+{
+	__meminfo_extra(m);
+
+	return 0;
+}
+
+static int __init proc_meminfo_extra_init(void)
+{
+	proc_create_single("meminfo_extra", 0, NULL, meminfo_extra_proc_show);
+	return 0;
+}
+fs_initcall(proc_meminfo_extra_init);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 52269e56c514..55317161ab57 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2898,6 +2898,10 @@ void __init setup_nr_node_ids(void);
 static inline void setup_nr_node_ids(void) {}
 #endif
 
+void show_meminfo_extra(void);
+int register_meminfo_extra(atomic_long_t *val, int shift, const char *name);
+int unregister_meminfo_extra(atomic_long_t *val);
+
 extern int memcmp_pages(struct page *page1, struct page *page2);
 
 static inline int pages_identical(struct page *page1, struct page *page2)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..db1be9a39783 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5229,6 +5229,7 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 	struct zone *zone;
 	pg_data_t *pgdat;
 
+	show_meminfo_extra();
 	for_each_populated_zone(zone) {
 		if (show_mem_node_skip(filter, zone_to_nid(zone), nodemask))
 			continue;
-- 
2.13.7