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

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Message-ID: <CA+55aFwMdZAVJLakx=xxY2QXaRdOxaPGMttU=P=2tH6+RNJeog@mail.gmail.com>
Date:	Tue, 10 Sep 2013 17:01:23 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	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>,
	Dave Chinner <dchinner@...hat.com>,
	Glauber Costa <glommer@...nvz.org>
Subject: Re: linux-next: manual merge of the akpm tree with Linus' tree

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...

           Linus
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