linux-ext4 - Re: [PATCH V10 10/11] fs: Introduce DCACHE

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Date:   Thu, 23 Apr 2020 16:38:25 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH V10 10/11] fs: Introduce DCACHE_DONTCACHE

On Fri, Apr 24, 2020 at 08:57:34AM +1000, Dave Chinner wrote:
> On Wed, Apr 22, 2020 at 02:21:01PM -0700, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.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@...iv.linux.org.uk>
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> 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...

That does follow an existing pattern.

Al?  Any preference?

Ira

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com