linux-kernel - Re: linux-next: manual merge of the akpm tree with Linus' tree

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Message-ID: <20130911003905.GD2445@devil.localdomain>
Date:	Wed, 11 Sep 2013 10:39:05 +1000
From:	Dave Chinner <dchinner@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next <linux-next@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Glauber Costa <glommer@...nvz.org>
Subject: Re: linux-next: manual merge of the akpm tree with Linus' tree

On Tue, Sep 10, 2013 at 05:01:23PM -0700, Linus Torvalds wrote:
> On Tue, Sep 10, 2013 at 4:53 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > list_lru_add() can fail if it's already on the list; leaving the counter
> > alone should've been conditional on that, setting the flag - no.  Said
> > that, it probably should be WARN_ON(!...); this_cpu_inc(); ... |= ...;
> 
> That WARN_ON_(!..) might indeed be better (maybe just WARN_ON_ONCE())..
> 
> That DCACHE_LRU_LIST bit needs to be coherent with "the dentry->d_lru
> entry is on _some_ list" (whether it's the dentry one or the shrinker
> one), so if that list_lru_add() ever fails, that would be a sign of
> badness.
> 
> And that whole function is very performance-critical, to the point
> where we not only don't want to call down to list_lry_add(), we don't
> even want to touch the d_lru list entry itself to even _look_ if it's
> empty or not, because that will take a cache miss. Which was obviously
> the whole reason for that DCACHE_LRU_LIST bit existing...

Guys, I'm about to be out of the office for 4-5 days, so this is
real bad timing for me. When I get back I'll put some effort into
validating that everything still works properly and performs as
expected.

Cheers,

Dave.
-- 
Dave Chinner
dchinner@...hat.com
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