linux-ext4 - Re: [PATCH V8 09/11] fs: Introduce DCACHE

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Date:   Wed, 15 Apr 2020 21:55:11 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-kernel@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V8 09/11] fs: Introduce DCACHE_DONTCACHE

On Wed, Apr 15, 2020 at 11:01:53AM +0200, Jan Kara wrote:
> On Tue 14-04-20 23:45:21, 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 which will flag I_DONTCACHE as well ad
> > DCACHE_DONTCACHE on all dentries point to a specified inode.
> 
> I think this sentence needs more work :). Like: Also add a helper function
> which will mark the inode with I_DONTCACHE flag and also mark all dentries
> pointing to a specified inode as DCACHE_DONTCACHE.
> 
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > 
> > ---
> > Changes from V7:
> > 	new patch
> > ---
> >  fs/dcache.c            |  4 ++++
> >  fs/inode.c             | 15 +++++++++++++++
> >  include/linux/dcache.h |  2 ++
> >  include/linux/fs.h     |  1 +
> >  4 files changed, 22 insertions(+)
> 
> ...
> 
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 93d9252a00ab..b8b1917a324e 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 flag_inode_dontcache(struct inode *inode)
> 
> mark_inode_dontcache?

That works.

> 
> > +{
> > +	struct dentry *dent;
> 
> This is really nitpicking but dentry variables are usually called 'de' or
> 'dentry' :)

Easy change.  done.

> 
> > +
> > +	rcu_read_lock();
> 
> I don't think this list is safe to traverse under RCU. E.g.
> dentry_unlink_inode() does hlist_del_init(&dentry->d_u.d_alias). Usually,
> we traverse this list under inode->i_lock protection AFAICS.

Ah...  not sure where I got that.  I thought I found this locked with rcu
somewhere but I obviously got confused.  And I did not even use the rcu version
of the list iterator...  :-(

I'll clean it up, thanks for the review,
Ira

> 
> 								Honza
> 
> > +	hlist_for_each_entry(dent, &inode->i_dentry, d_u.d_alias) {
> > +		spin_lock(&dent->d_lock);
> > +		dent->d_flags |= DCACHE_DONTCACHE;
> > +		spin_unlock(&dent->d_lock);
> > +	}
> > +	rcu_read_unlock();
> > +	inode->i_state |= I_DONTCACHE;
> > +}
> > +EXPORT_SYMBOL(flag_inode_dontcache);
> > +
> >  /*
> >   * Called when we're dropping the last reference
> >   * to an inode.
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR