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

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Date:	Thu, 12 Sep 2013 18:12:24 -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 Thu, Sep 12, 2013 at 5:56 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'll walk through the code, it looked suspicious. Maybe there's
> something subtle that makes it work, but I don't see it.

Btw, it's not just the DCACHE_LRU_LIST bit. The games with
"nr_dentry_unused" look totally broken too. It's decremented in
dentry_lru_isolate_shrink() for each dentry we remove, and then it is
decremented *again* in shrink_dcache_sb() by the number of dentries we
removed.

Maybe I'm confused, but the code sure looks more confused than I feel.

I would suggest keeping the same semantics for 'nr_dentry_unused'.
Dentries are unused whether they are on the "real" LRU list or have
been tagged with DCACHE_SHRINK_LIST. So moving from one list to the
other does nothing. It's the "list_del_init()" that should trigger
both 'nr_dentry_unused' and DCACHE_LRU_LIST bit-clearing.

In fact, maybe a helper function for _actually_ removing the thing
from all lists, and adding them back. Right now there are
"list_del_init()" and "list_add[_tail]()" calls sprinkled around in
random places, mixed up with the new "list_lru_add()".

Damn, the code is too confused. I have to go to a highschool parent
back-to-school meeting, so I won't get to this until maybe on a plane
tomorrow. Al, can you please give this a look?

             Linus
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