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

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Message-ID: <20200423225734.GY27860@dread.disaster.area>
Date:   Fri, 24 Apr 2020 08:57:34 +1000
From:   Dave Chinner <david@...morbit.com>
To:     ira.weiny@...el.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 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...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com