linux-kernel - Re: [patch 3/4] cpu alloc: The allocator

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Message-Id: <20081003012003.f1f84937.akpm@linux-foundation.org>
Date:	Fri, 3 Oct 2008 01:20:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	rusty@...tcorp.com.au, jeremy@...p.org, ebiederm@...ssion.com,
	travis@....com, herbert@...dor.apana.org.au, xemul@...nvz.org
Subject: Re: [patch 3/4] cpu alloc: The allocator

On Fri, 03 Oct 2008 10:43:31 +0300 Pekka Enberg <penberg@...helsinki.fi> wrote:

> Hi Andrew,
> 
> On Fri, 2008-10-03 at 00:33 -0700, Andrew Morton wrote:
> > > +static void set_map(int start, int length)
> > > +{
> > > +	while (length-- > 0)
> > > +		__set_bit(start++, cpu_alloc_map);
> > > +}
> > 
> > Can we use bitmap_fill() here?
> 
> But bitmap_fill() assumes that the starting offset is aligned to
> unsigned long (which is not the case here), doesn't it?

umm, yeah, the whole bitmap interface is busted from that POV.

> ___On Fri, 2008-10-03 at 00:33 -0700, Andrew Morton wrote:
> > But I'd have though that it would be possible to only allocate the
> > storage for online CPUs.  That would be a pretty significant win for
> > some system configurations?
> 
> Maybe, but then you'd have to deal with CPU hotplug... iik.

Of course.
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