linux-kernel - Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU symlinks

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Message-ID: <CA+55aFwsBkGOrYz_EhXhUB9cbjciV2nLxgd4NoHTjoTnjjGTLw@mail.gmail.com>
Date:	Sat, 16 May 2015 20:48:11 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	NeilBrown <neilb@...e.de>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger@...ger.ca>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU symlinks

On Sat, May 16, 2015 at 8:12 PM, NeilBrown <neilb@...e.de> wrote:
>
> The problem isn't getting intermediates.  The problem is that not having
> intermediates confuses the dcache.  When the dcache is just providing a
> caching service, and not providing a consistency service, then it shouldn't
> let itself get confused.

The dcache is much more than just a cache. It *is* in control. You may
not like it, but in the big picture, one odd filesystem not liking it
isn't a big deal.

Sorry, but that really is how it is. NFS isn't special enough for some
badly designed lookup models to matter one whit.  And caching si *so*
effective, that the actual lookup case isn't the primary thing.

Yes, you can find loads where caching doesn't work well. But they are
odd and not all that important. The cases where caches dominate are
*much* more common.

Designing things around the 1% case (or the 0.01%) would be completely
insane. The dcache and the vfs is designed for the 99.9% case.

           Linus
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