linux-kernel - Re: dcache shrink list corruption?

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Message-ID: <20140501025105.GY18016@ZenIV.linux.org.uk>
Date:	Thu, 1 May 2014 03:51:05 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: dcache shrink list corruption?

On Wed, Apr 30, 2014 at 05:18:23PM -0700, Linus Torvalds wrote:

> and then suddenly it looks like we have a common exit sequence from
> that dentry_kill() function, no?
> 
> (The earlier "unlock_on_failure" exit case is altogether a different case).
> 
> I dunno. Maybe not a big deal, but one reason I prefer doing that
> "free" flag is because I really tend to prefer the simple case of
> lock-unlock pairing cleanly at the same level. NOT the pattern where
> you have one lock at one indentation level, paired with multiple
> unlocks for all the different cases.

Yeah, but... I have such variant, but the best I could get still generated
the code that wasn't particulary nice.  Part might be gcc code generation
sucking for bool, part - extra register pressure...  It has slightly lower
i-cache footprint, though, so it might be worth doing.  Hell knows; that's a
fairly hot codepath, so let's do it that way - I've just pushed an alternative
branch with bool can_free variant; branches in question: vfs.git#for-linus and
vfs.git#dentry_kill-2. Help with profiling is needed; the loads to watch are
the ones where dentry_kill() + dentry_free() are sufficiently high in profiles
for the differences to matter.  Any takers?
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