Re: [PATCH] vfs: add d_prune dentry operation

[Sage Weil]

Hi Al,

Any chance we can get this in 3.1-rc1?  Not being able to use the dcache 
fully isn't doing good things to our metadata performance.

sage



On Fri, 8 Jul 2011, Sage Weil wrote:

> This adds a d_prune dentry operation that is called by the VFS prior to 
> pruning (i.e. unhashing and killing) a hashed dentry from the dcache. This 
> allows the file system to maintain visibility into the contents and 
> consistency of the dcache:
> 
>  - dentry eviction/pruning now calls into the fs
>  - any modifications (unlink, rename, create, etc.) are protected by 
>    i_mutex and call into the fs
> 
> This will be used by Ceph to maintain a flag indicating whether the 
> complete contents of a directory are contained in the dcache, allowing it 
> to satisfy lookups and readdir with cached results without additional 
> server communication.
> 
> Signed-off-by: Sage Weil <sage@xxxxxxxxxxxx>
> ---
>  Documentation/filesystems/Locking |    1 +
>  fs/dcache.c                       |    8 ++++++++
>  include/linux/dcache.h            |    3 +++
>  3 files changed, 12 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
> index 57d827d..b3fa7c8 100644
> --- a/Documentation/filesystems/Locking
> +++ b/Documentation/filesystems/Locking
> @@ -29,6 +29,7 @@ d_hash		no		no		no		maybe
>  d_compare:	yes		no		no		maybe
>  d_delete:	no		yes		no		no
>  d_release:	no		no		yes		no
> +d_prune:        no              yes             no              no
>  d_iput:		no		no		yes		no
>  d_dname:	no		no		no		no
>  d_automount:	no		no		yes		no
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 37f72ee..74d1a30 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -673,6 +673,8 @@ static void try_prune_one_dentry(struct dentry *dentry)
>  			spin_unlock(&dentry->d_lock);
>  			return;
>  		}
> +		if (dentry->d_flags & DCACHE_OP_PRUNE)
> +			dentry->d_op->d_prune(dentry);
>  		dentry = dentry_kill(dentry, 1);
>  	}
>  }
> @@ -879,6 +881,8 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
>  
>  	/* detach this root from the system */
>  	spin_lock(&dentry->d_lock);
> +	if (dentry->d_flags & DCACHE_OP_PRUNE)
> +		dentry->d_op->d_prune(dentry);
>  	dentry_lru_del(dentry);
>  	__d_drop(dentry);
>  	spin_unlock(&dentry->d_lock);
> @@ -895,6 +899,8 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
>  					    d_u.d_child) {
>  				spin_lock_nested(&loop->d_lock,
>  						DENTRY_D_LOCK_NESTED);
> +				if (dentry->d_flags & DCACHE_OP_PRUNE)
> +					dentry->d_op->d_prune(dentry);
>  				dentry_lru_del(loop);
>  				__d_drop(loop);
>  				spin_unlock(&loop->d_lock);
> @@ -1363,6 +1369,8 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
>  		dentry->d_flags |= DCACHE_OP_REVALIDATE;
>  	if (op->d_delete)
>  		dentry->d_flags |= DCACHE_OP_DELETE;
> +	if (op->d_prune)
> +		dentry->d_flags |= DCACHE_OP_PRUNE;
>  
>  }
>  EXPORT_SYMBOL(d_set_d_op);
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index 19d90a5..681f46f 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -165,6 +165,7 @@ struct dentry_operations {
>  			unsigned int, const char *, const struct qstr *);
>  	int (*d_delete)(const struct dentry *);
>  	void (*d_release)(struct dentry *);
> +	void (*d_prune)(struct dentry *);
>  	void (*d_iput)(struct dentry *, struct inode *);
>  	char *(*d_dname)(struct dentry *, char *, int);
>  	struct vfsmount *(*d_automount)(struct path *);
> @@ -219,6 +220,8 @@ struct dentry_operations {
>  #define DCACHE_MANAGED_DENTRY \
>  	(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
>  
> +#define DCACHE_OP_PRUNE         0x80000
> +
>  extern seqlock_t rename_lock;
>  
>  static inline int dname_external(struct dentry *dentry)
> -- 
> 1.7.0
> 
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