linux-kernel - Re: [PATCH 02/11] vfs: More precise tests in d

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Message-ID: <878utb3l7i.fsf@xmission.com>
Date:	Sat, 15 Feb 2014 17:22:41 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Rob Landley <rob@...dley.net>,
	Miklos Szeredi <miklos@...redi.hu>,
	Christoph Hellwig <hch@...radead.org>,
	Karel Zak <kzak@...hat.com>,
	"J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: [PATCH 02/11] vfs: More precise tests in d_invalidate

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Sat, Feb 15, 2014 at 3:23 PM, Eric W. Biederman
> <ebiederm@...ssion.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.

Thank you for taking the time to look.

It is also very true that I have been mostly focusing on the semantics
and correctness rather than on the performance of these changes.

I did keep a weather eye on the performance impact of these changes
though and as long as we can stand a slow down in the rare case where
mount points are present my changes should be fine.

Eric
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