Subject: Re: [PATCH v3 5/7] fs: new_inode_single() and iput_single()

From: "Paul E. McKenney" <[email-masked]>
Date: Tue, 16 Dec 2008 13:41:11 -0800

On Thu, Dec 11, 2008 at 11:40:07PM +0100, Eric Dumazet wrote:
> Goal of this patch is to not touch inode_lock for socket/pipes/anonfd
> inodes allocation/freeing.
> 
> SINGLE dentries are attached to inodes that dont need to be linked
> in a list of inodes, being "inode_in_use" or "sb->s_inodes"
> As inode_lock was taken only to protect these lists, we avoid taking it
> as well.
> 
> Using iput_single() from dput_single() avoids taking inode_lock
> at freeing time.
> 
> This patch has a very noticeable effect, because we avoid dirtying of
> three contended cache lines in new_inode(), and five cache lines in iput()
> 
> ("socketallocbench -n 8" result : from 19.9s to 3.01s)

Nice!

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

> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>  fs/anon_inodes.c   |    2 +-
>  fs/dcache.c        |    2 +-
>  fs/inode.c         |   29 ++++++++++++++++++++---------
>  fs/pipe.c          |    2 +-
>  include/linux/fs.h |   12 +++++++++++-
>  net/socket.c       |    2 +-
>  6 files changed, 35 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 8bf83cb..89fd36d 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -125,7 +125,7 @@ EXPORT_SYMBOL_GPL(anon_inode_getfd);
>   */
>  static struct inode *anon_inode_mkinode(void)
>  {
> -	struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
> +	struct inode *inode = new_inode_single(anon_inode_mnt->mnt_sb);
> 
>  	if (!inode)
>  		return ERR_PTR(-ENOMEM);
> diff --git a/fs/dcache.c b/fs/dcache.c
> index af3bfb3..3363853 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -231,7 +231,7 @@ static void dput_single(struct dentry *dentry)
>  		return;
>  	inode = dentry->d_inode;
>  	if (inode)
> -		iput(inode);
> +		iput_single(inode);
>  	d_free(dentry);
>  }
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index dc8e72a..0fdfe1b 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -221,6 +221,13 @@ void destroy_inode(struct inode *inode)
>  		kmem_cache_free(inode_cachep, (inode));
>  }
> 
> +void iput_single(struct inode *inode)
> +{
> +	if (atomic_dec_and_test(&inode->i_count)) {
> +		destroy_inode(inode);
> +		percpu_counter_dec(&nr_inodes);
> +	}
> +}
> 
>  /*
>   * These are initializations that only need to be done
> @@ -587,8 +594,9 @@ static int last_ino_get(void)
>  #endif
> 
>  /**
> - *	new_inode 	- obtain an inode
> + *	__new_inode 	- obtain an inode
>   *	@sb: superblock
> + *  @single: if true, dont link new inode in a list
>   *
>   *	Allocates a new inode for given superblock. The default gfp_mask
>   *	for allocations related to inode->i_mapping is GFP_HIGHUSER_PAGECACHE.
> @@ -598,7 +606,7 @@ static int last_ino_get(void)
>   *	newly created inode's mapping
>   *
>   */
> -struct inode *new_inode(struct super_block *sb)
> +struct inode *__new_inode(struct super_block *sb, int single)
>  {
>  	/*
>  	 * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
> @@ -607,22 +615,25 @@ struct inode *new_inode(struct super_block *sb)
>  	 */
>  	struct inode * inode;
> 
> -	spin_lock_prefetch(&inode_lock);
> -	
>  	inode = alloc_inode(sb);
>  	if (inode) {
>  		percpu_counter_inc(&nr_inodes);
>  		inode->i_state = 0;
>  		inode->i_ino = last_ino_get();
> -		spin_lock(&inode_lock);
> -		list_add(&inode->i_list, &inode_in_use);
> -		list_add(&inode->i_sb_list, &sb->s_inodes);
> -		spin_unlock(&inode_lock);
> + 		if (single) {
> +  			INIT_LIST_HEAD(&inode->i_list);
> +  			INIT_LIST_HEAD(&inode->i_sb_list);
> + 		} else {
> +			spin_lock(&inode_lock);
> +			list_add(&inode->i_list, &inode_in_use);
> +			list_add(&inode->i_sb_list, &sb->s_inodes);
> +			spin_unlock(&inode_lock);
> +		}
>  	}
>  	return inode;
>  }
> 
> -EXPORT_SYMBOL(new_inode);
> +EXPORT_SYMBOL(__new_inode);
> 
>  void unlock_new_inode(struct inode *inode)
>  {
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 4de6dd5..8c51a0d 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -865,7 +865,7 @@ static struct dentry_operations pipefs_dentry_operations = {
> 
>  static struct inode * get_pipe_inode(void)
>  {
> -	struct inode *inode = new_inode(pipe_mnt->mnt_sb);
> +	struct inode *inode = new_inode_single(pipe_mnt->mnt_sb);
>  	struct pipe_inode_info *pipe;
> 
>  	if (!inode)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index a789346..a702d81 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1899,7 +1899,17 @@ extern void __iget(struct inode * inode);
>  extern void iget_failed(struct inode *);
>  extern void clear_inode(struct inode *);
>  extern void destroy_inode(struct inode *);
> -extern struct inode *new_inode(struct super_block *);
> +extern struct inode *__new_inode(struct super_block *, int);
> +static inline struct inode *new_inode(struct super_block *sb)
> +{
> +	return __new_inode(sb, 0);
> +}
> +static inline struct inode *new_inode_single(struct super_block *sb)
> +{
> +	return __new_inode(sb, 1);
> +}
> +extern void iput_single(struct inode *);
> +
>  extern int should_remove_suid(struct dentry *);
>  extern int file_remove_suid(struct file *);
> 
> diff --git a/net/socket.c b/net/socket.c
> index 353c928..4017409 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -464,7 +464,7 @@ static struct socket *sock_alloc(void)
>  	struct inode *inode;
>  	struct socket *sock;
> 
> -	inode = new_inode(sock_mnt->mnt_sb);
> +	inode = new_inode_single(sock_mnt->mnt_sb);
>  	if (!inode)
>  		return NULL;
> 
> --
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