[RFC PATCH 3/3] fs: report per-mount io stats

[Amir Goldstein <amir73il@gmail.com>]

Show optional collected per-mount io stats in /proc/<pid>/mountstats
for filesystems that do not implement their own show_stats() method.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

See following snippet from mountstats example report:

device overlay mounted on /mnt with fstype overlay
	times: 125 153
	rchar: 12
	wchar: 0
	syscr: 2
	syscw: 0

Thanks,
Amir.

 fs/mount.h          |  1 +
 fs/namespace.c      |  2 ++
 fs/proc_namespace.c | 13 +++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/fs/mount.h b/fs/mount.h
index 81db83c36140..1f262892a6ed 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -91,6 +91,7 @@ struct mount {
 	int mnt_id;			/* mount identifier */
 	int mnt_group_id;		/* peer group identifier */
 	int mnt_expiry_mark;		/* true if marked for expiry */
+	time64_t mnt_time;		/* time of mount */
 	struct hlist_head mnt_pins;
 	struct hlist_head mnt_stuck_children;
 } __randomize_layout;
diff --git a/fs/namespace.c b/fs/namespace.c
index 04b35dfcc71f..3a91234e5fd0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -198,6 +198,8 @@ static struct mount *alloc_vfsmnt(const char *name)
 		mnt->mnt_count = 1;
 		mnt->mnt_writers = 0;
 #endif
+		/* For proc/<pid>/mountstats */
+		mnt->mnt_time = ktime_get_seconds();
 
 		INIT_HLIST_NODE(&mnt->mnt_hash);
 		INIT_LIST_HEAD(&mnt->mnt_child);
diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index eafb75755fa3..34aea7f3f550 100644
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -229,6 +229,19 @@ static int show_vfsstat(struct seq_file *m, struct vfsmount *mnt)
 	if (sb->s_op->show_stats) {
 		seq_putc(m, ' ');
 		err = sb->s_op->show_stats(m, mnt_path.dentry);
+	} else if (mnt_has_stats(mnt)) {
+		/* Similar to /proc/<pid>/io */
+		seq_printf(m, "\n"
+			   "\ttimes: %lld %lld\n"
+			   "\trchar: %lld\n"
+			   "\twchar: %lld\n"
+			   "\tsyscr: %lld\n"
+			   "\tsyscw: %lld\n",
+			   r->mnt_time, ktime_get_seconds(),
+			   mnt_iostats_counter_read(r, MNTIOS_CHARS_RD),
+			   mnt_iostats_counter_read(r, MNTIOS_CHARS_WR),
+			   mnt_iostats_counter_read(r, MNTIOS_SYSCALLS_RD),
+			   mnt_iostats_counter_read(r, MNTIOS_SYSCALLS_WR));
 	}
 
 	seq_putc(m, '\n');
-- 
2.25.1