linux-kernel - Re: [PATCH -mm 2/2] Introduce freezer flags

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Message-ID: <20070428070716.GH2994@elf.ucw.cz>
Date:	Sat, 28 Apr 2007 09:07:16 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ego@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...sign.ru>,
	Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm 2/2] Introduce freezer flags

Hi!

> > > > > > +#ifdef CONFIG_FREEZER
> > > > > > +	/* Used by the process freezer, defined in freezer.h */
> > > > > > +	unsigned int freezer_flags;
> > > > > 
> > > > > unsigned long freezer_flags; ??
> > > > 
> > > > I guess so.
> > > 
> > > Still, on x86_64, for example, we'll waste 4 bytes by using 'unsigned long'
> > > here, which I wouldn't like to do.
> > > 
> > > Is it acceptable to use explicit type casting in set_bit() and friends?
> > 
> > I'm afraid set_bit & friends are only defined on unsigned long.
> 
> On x86_64 they are defined on anything, even on huge bitmaps.
> 
> > You can cast, but you may run into some nasty surprise... like damaging
> > surrounding bytes on 64-bit architectures != x86_64.
> 
> Let's use unsigned long, then, but I'm not really happy with that.

Ask the architecture people, but comments like

/data/l/linux/include/linux/agpgart.h:  long access_flags;      /* long req'd for set_bit --RR */

Make me think long is needed.

 * bitmaps provide bit arrays that consume one or more unsigned
 * longs.  The bitmap interface and available operations are listed
 * here, in bitmap.h

...I'm afraid we need ulongs.
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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