linux-kernel - Re: [PATCH 1/5][RFC][CFT] percpu fixes, part 1

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Message-ID: <20140306204726.GE14033@htj.dyndns.org>
Date:	Thu, 6 Mar 2014 15:47:26 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Stephen Tweedie <sct@...hat.com>,
	Jeremy Eder <jeder@...hat.com>
Subject: Re: [PATCH 1/5][RFC][CFT] percpu fixes, part 1

Hello, Al.

On Thu, Mar 06, 2014 at 08:30:30PM +0000, Al Viro wrote:
> > Also, I think it'd be better to split addition of first_free hint to a
> > separate patch.
> 
> OK, but I'm not sure how much does it simplify things, actually.

Not much, but it should at least help bisection if something goes
wrong, I think.

> > A comment explaining why ignoring the free bit during bin search is
> > okay would be nice?
> 
> Huh?  We are not ignoring it - we are searching for exact value, including
> the lower bit being set.  It might be worth adding a comment next to
> "freeme |= 1;" before the loop, but that's it.  These two BUG_ON() fold

Oh yeah, nothing too much.  I was just thinking about noting that
looking for the exact match is enough as we're looking for the
matching busy slot and the bit itself can't change ordering between
entries.

> > > +	if (unlikely(align < 2))
> > > +		align = 2;
> > 
> > Please add a comment explaining why the above min alignment is
> > necessary.
> 
> Umm...  Will "we want the lowest bit of offset available for free/in_use
> indicator" do?

Yeap.

Thanks!

-- 
tejun
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