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Date: Sat, 15 Feb 2014 16:03:53 -0800
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Subject: Re: [PATCH 02/11] vfs: More precise tests in d_invalidate
From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, "Serge E. Hallyn" <serge@hallyn.com>,
        Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>, Rob Landley <rob@landley.net>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Christoph Hellwig <hch@infradead.org>, Karel Zak <kzak@redhat.com>,
        "J. Bruce Fields" <bfields@fieldses.org>
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On Sat, Feb 15, 2014 at 3:23 PM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> Except that today d_invalidate drops the dcache lock and
> calls shrink_dcache_parent.  Which gets you into exactly the same
> complex "walk parents and check all siblings" code.

Hmm. It only does that for directories that have sub-entries, though.

I think you may care just about directories (because that's what your
series is about), but d_invalidate() is used for other cases too,
notably d_revalidate() (ie things like stale NFS lookups of normal
files).

That said, I'll have to think about this more. If d_subdir is empty, I
guess d_walk() will be fairly cheap. It's very different, but maybe
not as disastrous as I thought.

                Linus