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

Darrick J. Wong
2020-04-28T20:10:48Z

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
>