[RFC PATCH 1/3] fs: add iostats counters to struct mount

[Amir Goldstein <amir73il@gmail.com>]

With config MOUNT_IO_STATS, add an array of counters to struct mnt_pcp
that will be used to collect I/O statistics.

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

Please note that the dependency on SMP is just for the RFC.

Thanks,
Amir.

 fs/Kconfig     |  9 +++++++++
 fs/mount.h     | 32 ++++++++++++++++++++++++++++++++
 fs/namespace.c | 17 +++++++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/fs/Kconfig b/fs/Kconfig
index aa4c12282301..7473bdf4bbfb 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -15,6 +15,15 @@ config VALIDATE_FS_PARSER
 	  Enable this to perform validation of the parameter description for a
 	  filesystem when it is registered.
 
+config FS_MOUNT_STATS
+	bool "Enable per-mount I/O statistics"
+	depends on SMP
+	help
+	  Enable this to allow collecting per-mount I/O statistics and display
+	  them in /proc/<pid>/mountstats.
+
+	  Say N if unsure.
+
 if BLOCK
 
 config FS_IOMAP
diff --git a/fs/mount.h b/fs/mount.h
index ce6c376e0bc2..2bf0df64ded5 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -24,9 +24,25 @@ struct mnt_namespace {
 	unsigned int		pending_mounts;
 } __randomize_layout;
 
+/* Similar to task_io_accounting members */
+enum {
+	MNTIOS_CHARS_RD,	/* bytes read via syscalls */
+	MNTIOS_CHARS_WR,	/* bytes written via syscalls */
+	MNTIOS_SYSCALLS_RD,	/* # of read syscalls */
+	MNTIOS_SYSCALLS_WR,	/* # of write syscalls */
+	_MNTIOS_COUNTERS_NUM
+};
+
+struct mnt_iostats {
+	s64 counter[_MNTIOS_COUNTERS_NUM];
+};
+
 struct mnt_pcp {
 	int mnt_count;
 	int mnt_writers;
+#ifdef CONFIG_FS_MOUNT_STATS
+	struct mnt_iostats iostats;
+#endif
 };
 
 struct mountpoint {
@@ -158,3 +174,19 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
 }
 
 extern void mnt_cursor_del(struct mnt_namespace *ns, struct mount *cursor);
+
+static inline void mnt_iostats_counter_inc(struct mount *mnt, int id)
+{
+#ifdef CONFIG_FS_MOUNT_STATS
+	this_cpu_inc(mnt->mnt_pcp->iostats.counter[id]);
+#endif
+}
+
+static inline void mnt_iostats_counter_add(struct mount *mnt, int id, s64 n)
+{
+#ifdef CONFIG_FS_MOUNT_STATS
+	this_cpu_add(mnt->mnt_pcp->iostats.counter[id], n);
+#endif
+}
+
+extern s64 mnt_iostats_counter_read(struct mount *mnt, int id);
diff --git a/fs/namespace.c b/fs/namespace.c
index d2db7dfe232b..04b35dfcc71f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -283,6 +283,23 @@ static unsigned int mnt_get_writers(struct mount *mnt)
 #endif
 }
 
+s64 mnt_iostats_counter_read(struct mount *mnt, int id)
+{
+	s64 count = 0;
+#ifdef CONFIG_FS_MOUNT_STATS
+	/*
+	 * MOUNT_STATS depends on SMP.
+	 * Should be trivial to implement for !SMP if anyone cares...
+	 */
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		count += per_cpu_ptr(mnt->mnt_pcp, cpu)->iostats.counter[id];
+	}
+#endif
+	return count;
+}
+
 static int mnt_is_readonly(struct vfsmount *mnt)
 {
 	if (mnt->mnt_sb->s_readonly_remount)
-- 
2.25.1