Re: [PATCH 02/11] vfs: More precise tests in d_invalidate

[Eric W. Biederman]

Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:

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