Re: [PATCH V11 10/11] fs: Introduce DCACHE_DONTCACHE

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Apr 27, 2020 at 05:21:41PM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> DCACHE_DONTCACHE indicates a dentry should not be cached on final
> dput().
> 
> Also add a helper function to mark DCACHE_DONTCACHE on all dentries
> pointing to a specific inode when that inode is being set I_DONTCACHE.
> 
> This facilitates dropping dentry references to inodes sooner which
> require eviction to swap S_DAX mode.
> 
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>

Seems reasonable to me,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> 
> ---
> Changes from V10:
> 	rename to d_mark_dontcache()
> 	Move function to fs/dcache.c
> 
> Changes from V9:
> 	modify i_state under i_lock
> 	Update comment
> 		"Purge from memory on final dput()"
> 
> Changes from V8:
> 	Update commit message
> 	Use mark_inode_dontcache in XFS
> 	Fix locking...  can't use rcu here.
> 	Change name to mark_inode_dontcache
> ---
>  fs/dcache.c            | 19 +++++++++++++++++++
>  fs/xfs/xfs_icache.c    |  2 +-
>  include/linux/dcache.h |  2 ++
>  include/linux/fs.h     |  1 +
>  4 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index b280e07e162b..0d07fb335b78 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -647,6 +647,10 @@ static inline bool retain_dentry(struct dentry *dentry)
>  		if (dentry->d_op->d_delete(dentry))
>  			return false;
>  	}
> +
> +	if (unlikely(dentry->d_flags & DCACHE_DONTCACHE))
> +		return false;
> +
>  	/* retain; LRU fodder */
>  	dentry->d_lockref.count--;
>  	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
> @@ -656,6 +660,21 @@ static inline bool retain_dentry(struct dentry *dentry)
>  	return true;
>  }
>  
> +void d_mark_dontcache(struct inode *inode)
> +{
> +	struct dentry *de;
> +
> +	spin_lock(&inode->i_lock);
> +	hlist_for_each_entry(de, &inode->i_dentry, d_u.d_alias) {
> +		spin_lock(&de->d_lock);
> +		de->d_flags |= DCACHE_DONTCACHE;
> +		spin_unlock(&de->d_lock);
> +	}
> +	inode->i_state |= I_DONTCACHE;
> +	spin_unlock(&inode->i_lock);
> +}
> +EXPORT_SYMBOL(d_mark_dontcache);
> +
>  /*
>   * Finish off a dentry we've decided to kill.
>   * dentry->d_lock must be held, returns with it unlocked.
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index de76f7f60695..888646d74d7d 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -559,7 +559,7 @@ xfs_iget_cache_miss(
>  	 */
>  	iflags = XFS_INEW;
>  	if (flags & XFS_IGET_DONTCACHE)
> -		VFS_I(ip)->i_state |= I_DONTCACHE;
> +		d_mark_dontcache(VFS_I(ip));
>  	ip->i_udquot = NULL;
>  	ip->i_gdquot = NULL;
>  	ip->i_pdquot = NULL;
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index c1488cc84fd9..a81f0c3cf352 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -177,6 +177,8 @@ struct dentry_operations {
>  
>  #define DCACHE_REFERENCED		0x00000040 /* Recently used, don't discard. */
>  
> +#define DCACHE_DONTCACHE		0x00000080 /* Purge from memory on final dput() */
> +
>  #define DCACHE_CANT_MOUNT		0x00000100
>  #define DCACHE_GENOCIDE			0x00000200
>  #define DCACHE_SHRINK_LIST		0x00000400
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 44bd45af760f..7c3e8c0306e0 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3055,6 +3055,7 @@ static inline int generic_drop_inode(struct inode *inode)
>  	return !inode->i_nlink || inode_unhashed(inode) ||
>  		(inode->i_state & I_DONTCACHE);
>  }
> +extern void d_mark_dontcache(struct inode *inode);
>  
>  extern struct inode *ilookup5_nowait(struct super_block *sb,
>  		unsigned long hashval, int (*test)(struct inode *, void *),
> -- 
> 2.25.1
>