Re: [PATCH v2 4/6] fs: report per-mount io stats

On Mon, Feb 28, 2022 at 01:39:08PM +0200, Amir Goldstein wrote:
> Show optional collected per-mount io stats in /proc/<pid>/mountstats
> for filesystems that do not implement their own show_stats() method
> and opted-in to generic per-mount stats with FS_MOUNT_STATS flag.
> 
> Signed-off-by: Amir Goldstein <[email protected]>
> ---
>  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 f98bf4cd5b1a..2ab6308af78b 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 3fb8f11a42a1..546f07ed44c5 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -220,6 +220,8 @@ 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 49650e54d2f8..d744fb8543f5 100644
> --- a/fs/proc_namespace.c
> +++ b/fs/proc_namespace.c
> @@ -232,6 +232,19 @@ 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));

This doesn't scale as {cpus, mounts, counters, read frequency}
matrix explodes.  Please iterate the per-mount per cpu counters
once, adding up all counters in one pass to an array on stack, then
print them all from the array.

Cheers,

Dave.
-- 
Dave Chinner
[email protected]