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

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Message-ID: <20130913200000.GT13318@ZenIV.linux.org.uk>
Date:	Fri, 13 Sep 2013 21:00:00 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 Fri, Sep 13, 2013 at 12:12:20PM -0700, Linus Torvalds wrote:

> It tries to consolidate the dentry LRU stuff into a few helper
> functions that right now have anal checking of the flags. Maybe I
> overdid it, but the code was really confusing, and I think we got the
> free dentry counts wrong, and the bits wrong too, so I tried to be
> extra careful.
> 
> There are several cases:
>  - d_lru_add/del: fairly obvious
>  - d_lru_isolate: this is when the LRU callbacks ask us to remove the
> entry from the list. This is different from d_lru_del() only in that
> it uses the raw list removal, not the lru list helper function. I'm
> not sure that's right, but that's what the code used to do.

It is right - for one thing, we are holding the lock on that LRU list,
so list_lru_del() would deadlock right there.  For another, the same
list_lru_walk (OK, list_lru_walk_node()) will do ->nr_items decrement
when we return LRU_REMOVED to it, so we don't want to do it twice.
Plain list_del_init() is correct here.

>  - d_lru_shrink_move: move from the "global" lru list to a private shrinker list
>  - d_shrink_add/del: fairly obvious.
> 
> And then "denty_lru_add/del" that actually take the current state into
> account and do the right thing. Those we had before, I'm just
> explaining the difference from the low-level operations that have
> fixed "from this state to that" semantics

Looks sane; FWIW, the variant I'm playing with uses two independent
flags for "shrinker" and "per-sb", but AFAICS that doesn't yield better
code.  Feel free to slap my acked-by on it.
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