Subject: Re: [PATCH v3 2/7] fs: Use a percpu_counter to track nr_inodes

From: "Paul E. McKenney" <[email-masked]>
Date: Tue, 16 Dec 2008 13:10:53 -0800

On Thu, Dec 11, 2008 at 11:39:10PM +0100, Eric Dumazet wrote:
> Avoids cache line ping pongs between cpus and prepare next patch,
> because updates of nr_inodes dont need inode_lock anymore.
> 
> (socket8 bench result : no difference at this point)

I do like this per-CPU counter infrastructure!

One small comment change noted below.  Other than that:

Reviewed-by: Paul E. McKenney <[email-masked]>

> Signed-off-by: Eric Dumazet <dada1-fPLkHRcR87vqlBn2x/[email-masked]>
> ---
>  fs/fs-writeback.c   |    2 +-
>  fs/inode.c          |   39 +++++++++++++++++++++++++++++++--------
>  include/linux/fs.h  |    3 +++
>  kernel/sysctl.c     |    4 ++--
>  mm/page-writeback.c |    2 +-
>  5 files changed, 38 insertions(+), 12 deletions(-)
> 
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index d0ff0b8..b591cdd 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -608,7 +608,7 @@ void sync_inodes_sb(struct super_block *sb, int wait)
>  	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
> 
>  	wbc.nr_to_write = nr_dirty + nr_unstable +
> -			(inodes_stat.nr_inodes - inodes_stat.nr_unused) +
> +			(get_nr_inodes() - inodes_stat.nr_unused) +
>  			nr_dirty + nr_unstable;
>  	wbc.nr_to_write += wbc.nr_to_write / 2;		/* Bit more for luck */
>  	sync_sb_inodes(sb, &wbc);
> diff --git a/fs/inode.c b/fs/inode.c
> index 0487ddb..f94f889 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -96,9 +96,33 @@ static DEFINE_MUTEX(iprune_mutex);
>   * Statistics gathering..
>   */
>  struct inodes_stat_t inodes_stat;
> +static struct percpu_counter nr_inodes;
> 
>  static struct kmem_cache * inode_cachep __read_mostly;
> 
> +int get_nr_inodes(void)
> +{
> +	return percpu_counter_sum_positive(&nr_inodes);
> +}
> +
> +/*
> + * Handle nr_dentry sysctl

That would be "nr_inode", right?

> + */
> +#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
> +int proc_nr_inodes(ctl_table *table, int write, struct file *filp,
> +		   void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> +	inodes_stat.nr_inodes = get_nr_inodes();
> +	return proc_dointvec(table, write, filp, buffer, lenp, ppos);
> +}
> +#else
> +int proc_nr_inodes(ctl_table *table, int write, struct file *filp,
> +		   void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> +	return -ENOSYS;
> +}
> +#endif
> +
>  static void wake_up_inode(struct inode *inode)
>  {
>  	/*
> @@ -306,9 +330,7 @@ static void dispose_list(struct list_head *head)
>  		destroy_inode(inode);
>  		nr_disposed++;
>  	}
> -	spin_lock(&inode_lock);
> -	inodes_stat.nr_inodes -= nr_disposed;
> -	spin_unlock(&inode_lock);
> +	percpu_counter_sub(&nr_inodes, nr_disposed);
>  }
> 
>  /*
> @@ -560,8 +582,8 @@ struct inode *new_inode(struct super_block *sb)
>  	
>  	inode = alloc_inode(sb);
>  	if (inode) {
> +		percpu_counter_inc(&nr_inodes);
>  		spin_lock(&inode_lock);
> -		inodes_stat.nr_inodes++;
>  		list_add(&inode->i_list, &inode_in_use);
>  		list_add(&inode->i_sb_list, &sb->s_inodes);
>  		inode->i_ino = ++last_ino;
> @@ -622,7 +644,7 @@ static struct inode * get_new_inode(struct super_block *sb, struct hlist_head *h
>  			if (set(inode, data))
>  				goto set_failed;
> 
> -			inodes_stat.nr_inodes++;
> +			percpu_counter_inc(&nr_inodes);
>  			list_add(&inode->i_list, &inode_in_use);
>  			list_add(&inode->i_sb_list, &sb->s_inodes);
>  			hlist_add_head(&inode->i_hash, head);
> @@ -671,7 +693,7 @@ static struct inode * get_new_inode_fast(struct super_block *sb, struct hlist_he
>  		old = find_inode_fast(sb, head, ino);
>  		if (!old) {
>  			inode->i_ino = ino;
> -			inodes_stat.nr_inodes++;
> +			percpu_counter_inc(&nr_inodes);
>  			list_add(&inode->i_list, &inode_in_use);
>  			list_add(&inode->i_sb_list, &sb->s_inodes);
>  			hlist_add_head(&inode->i_hash, head);
> @@ -1042,8 +1064,8 @@ void generic_delete_inode(struct inode *inode)
>  	list_del_init(&inode->i_list);
>  	list_del_init(&inode->i_sb_list);
>  	inode->i_state |= I_FREEING;
> -	inodes_stat.nr_inodes--;
>  	spin_unlock(&inode_lock);
> +	percpu_counter_dec(&nr_inodes);
> 
>  	security_inode_delete(inode);
> 
> @@ -1093,8 +1115,8 @@ static void generic_forget_inode(struct inode *inode)
>  	list_del_init(&inode->i_list);
>  	list_del_init(&inode->i_sb_list);
>  	inode->i_state |= I_FREEING;
> -	inodes_stat.nr_inodes--;
>  	spin_unlock(&inode_lock);
> +	percpu_counter_dec(&nr_inodes);
>  	if (inode->i_data.nrpages)
>  		truncate_inode_pages(&inode->i_data, 0);
>  	clear_inode(inode);
> @@ -1394,6 +1416,7 @@ void __init inode_init(void)
>  {
>  	int loop;
> 
> +	percpu_counter_init(&nr_inodes, 0);
>  	/* inode slab cache */
>  	inode_cachep = kmem_cache_create("inode_cache",
>  					 sizeof(struct inode),
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 114cb65..a789346 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -47,6 +47,7 @@ struct inodes_stat_t {
>  	int dummy[5];		/* padding for sysctl ABI compatibility */
>  };
>  extern struct inodes_stat_t inodes_stat;
> +extern int get_nr_inodes(void);
> 
>  extern int leases_enable, lease_break_time;
> 
> @@ -2219,6 +2220,8 @@ int proc_nr_files(struct ctl_table *table, int write, struct file *filp,
>  		  void __user *buffer, size_t *lenp, loff_t *ppos);
>  int proc_nr_dentry(struct ctl_table *table, int write, struct file *filp,
>  		   void __user *buffer, size_t *lenp, loff_t *ppos);
> +int proc_nr_inodes(struct ctl_table *table, int write, struct file *filp,
> +		   void __user *buffer, size_t *lenp, loff_t *ppos);
> 
>  int get_filesystem_list(char * buf);
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 777bee7..b705f3a 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1205,7 +1205,7 @@ static struct ctl_table fs_table[] = {
>  		.data		= &inodes_stat,
>  		.maxlen		= 2*sizeof(int),
>  		.mode		= 0444,
> -		.proc_handler	= &proc_dointvec,
> +		.proc_handler	= &proc_nr_inodes,
>  	},
>  	{
>  		.ctl_name	= FS_STATINODE,
> @@ -1213,7 +1213,7 @@ static struct ctl_table fs_table[] = {
>  		.data		= &inodes_stat,
>  		.maxlen		= 7*sizeof(int),
>  		.mode		= 0444,
> -		.proc_handler	= &proc_dointvec,
> +		.proc_handler	= &proc_nr_inodes,
>  	},
>  	{
>  		.procname	= "file-nr",
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2970e35..a71a922 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -705,7 +705,7 @@ static void wb_kupdate(unsigned long arg)
>  	next_jif = start_jif + dirty_writeback_interval;
>  	nr_to_write = global_page_state(NR_FILE_DIRTY) +
>  			global_page_state(NR_UNSTABLE_NFS) +
> -			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
> +			(get_nr_inodes() - inodes_stat.nr_unused);
>  	while (nr_to_write > 0) {
>  		wbc.more_io = 0;
>  		wbc.encountered_congestion = 0;