linux-kernel - Re: [Patch 09/18] fs/logfs/gc.c

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Message-ID: <20070604090126.GB14823@lazybastard.org>
Date:	Mon, 4 Jun 2007 11:01:26 +0200
From:	Jörn Engel <joern@...ybastard.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org, akpm@...l.org,
	Sam Ravnborg <sam@...nborg.org>,
	John Stoffel <john@...ffel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Jamie Lokier <jamie@...reable.org>,
	Artem Bityutskiy <dedekind@...radead.org>,
	CaT <cat@....com.au>, Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	David Weinehall <tao@....umu.se>, Willy Tarreau <w@....eu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Dongjun Shin <djshin90@...il.com>, Pavel Machek <pavel@....cz>,
	Bill Davidsen <davidsen@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Albert Cahalan <acahalan@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Roland Dreier <rdreier@...co.com>,
	Ondrej Zajicek <santiago@...reenet.org>,
	Ulisses Furquim <ulissesf@...il.com>
Subject: Re: [Patch 09/18] fs/logfs/gc.c

On Mon, 4 June 2007 00:07:36 +0200, Arnd Bergmann wrote:
> On Sunday 03 June 2007, Jörn Engel wrote:
> > +static long decay(long t0, long t, long theta)
> > +{
> > +       long shift, fac;
> > +
> > +       if (t >= 32*theta)
> > +               return 0;
> > +
> > +       shift = t/theta;
> > +       fac = theta - (t%theta)/2;
> > +       return (t0 >> shift) * fac / theta;
> > +}
> 
> I think it's confusion to work with 'long' arguments
> here. If you actually allow larger than 32 bit arguments,
> that means that the gc logic behaves differently on
> 32 and 64 bit CPUs, which I don't think is what you
> intended.

Different behaviour would be fine.  This function will be used to pick
good candidates for garbage collection.  If one segment will get chosen
over another depending on BITS_PER_LONG, either one would have been a
good candidate anyway.

Hmm.  Maybe I should s/32/BITS_PER_LONG/ in the function.

> Also, can any of the arguments be negative? How about
> making them all explicit u32 and u64 variables?

That would make sense, yes.

Jörn

-- 
I've never met a human being who would want to read 17,000 pages of
documentation, and if there was, I'd kill him to get him out of the
gene pool.
-- Joseph Costello
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