Re: [PATCH V9 09/11] fs: Introduce DCACHE_DONTCACHE

[Ira Weiny <ira.weiny@intel.com>]

On Wed, Apr 22, 2020 at 10:46:47AM +0200, Jan Kara wrote:
> On Tue 21-04-20 12:17:51, 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>
> > 
> > ---
> > 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            |  4 ++++
> >  fs/inode.c             | 15 +++++++++++++++
> >  fs/xfs/xfs_icache.c    |  2 +-
> >  include/linux/dcache.h |  2 ++
> >  include/linux/fs.h     |  1 +
> >  5 files changed, 23 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index b280e07e162b..0030fabab2c4 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)))
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 93d9252a00ab..da7f3c4926cd 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -1526,6 +1526,21 @@ int generic_delete_inode(struct inode *inode)
> >  }
> >  EXPORT_SYMBOL(generic_delete_inode);
> >  
> > +void mark_inode_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);
> > +	}
> > +	spin_unlock(&inode->i_lock);
> > +	inode->i_state |= I_DONTCACHE;
> 
> Modification of i_state should happen under i_lock.

Done.

> 
> > +}
> > +EXPORT_SYMBOL(mark_inode_dontcache);
> > +
> >  /*
> >   * Called when we're dropping the last reference
> >   * to an inode.
> > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> > index de76f7f60695..3c8f44477804 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;
> > +		mark_inode_dontcache(VFS_I(ip));
> 
> And I know here modification of i_state didn't happen under i_lock but
> that's a special case because we are just instantiating the inode so it was
> not a real issue.

Thanks!
Ira

> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR