linux-kernel - Re: [rfc][patch] store-free path walking

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Message-ID: <alpine.LFD.2.01.0910071222230.3432@localhost.localdomain>
Date:	Wed, 7 Oct 2009 12:25:03 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [rfc][patch] store-free path walking

On Wed, 7 Oct 2009, Nick Piggin wrote:
> 
> Oh I did that, used a "seqcount" which is the bare sequence counter
> (and update it while holding d_lock).

Oh, I didn't notice, for a really silly reason: I looked at how you had 
changed DNAME_INLINE_LEN_MIN on 64-bit, and noticed that you were using 8 
bytes for your sequence lock.

But that's only true due to the padding things, and the seqcount itself is 
indeed just 4 bytes. 

Sad. But we do have the added requirement that we want to keep the 
commonly used fields together in the same cacheline, so maybe it's 
unavoidable.

		Linus
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