linux-kernel - Re: [PATCH] dcache: fix d_splice

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Message-ID: <CAJfpegumqYe2oQ3at8w8OJFhNx38c6XBtdnyb4H6O=AGihfH-Q@mail.gmail.com>
Date:	Thu, 16 Jan 2014 17:13:28 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Miklos Szeredi <mszeredi@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux NFS list <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH] dcache: fix d_splice_alias handling of aliases

On Thu, Jan 16, 2014 at 4:41 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
> And, sorry, I did miss that you said "non-directory".  But I think you
> have that backwards: d_splice_alias looks like:
>
>         if (inode && S_ISDIR(inode->i_mode)) {
>                 ...
>         } else {
>                 d_instantiate(dentry, inode);
>                 if (d_unhashed(dentry))
>                         d_rehash(dentry);
>         }
>
> So it ignores any existing aliases in the non-directory case.

Okay.

>
> d_materialise_unique by contrast calls __d_instantiate_unique, which
> looks like it should avoid adding duplicates.
>
> So I think switching everyone to d_materialiase_unique would result in
> fewer dentries.  But I've never seen any complaint about the issue and
> like you don't see a reason this would matter much either way.

So, yes, d_materialise_unique() looks like it has superior
functionality compared to d_splice_alias().

Thanks,
Miklos
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