Re: [PATCH V10 10/11] fs: Introduce DCACHE_DONTCACHE

[Dave Chinner]

On Wed, Apr 22, 2020 at 02:21:01PM -0700, ira.weiny@xxxxxxxxx wrote:
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>

Code looks fine....

> --- 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);
> +	}
> +	inode->i_state |= I_DONTCACHE;
> +	spin_unlock(&inode->i_lock);
> +}
> +EXPORT_SYMBOL(mark_inode_dontcache);

Though I suspect that this should be in fs/dcache.c and not
fs/inode.c. i.e. nothing in fs/inode.c does dentry list walks, but
there are several cases in the dcache code where inode dentry walks
are done under the inode lock (e.g. d_find_alias(inode)).

So perhaps this should be d_mark_dontcache(inode), which also marks
the inode as I_DONTCACHE so that everything is evicted on last
reference...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx