linux-kernel - Re: [patch 01/28] cpu alloc: The allocator

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Message-ID: <Pine.LNX.4.64.0711081031420.7871@schroedinger.engr.sgi.com>
Date:	Thu, 8 Nov 2007 10:33:26 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	akpm@...ux-foundation.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch 01/28] cpu alloc: The allocator

On Thu, 8 Nov 2007, Peter Zijlstra wrote:

> On Tue, 2007-11-06 at 11:51 -0800, Christoph Lameter wrote:
> 
> > +/*
> > + * Lock to protect the bitmap and the meta data for the cpu allocator.
> > + */
> > +static DEFINE_SPINLOCK(cpu_alloc_map_lock);
> 
> I thought you got nightmares from global locks :-)

Yes but this one is rarely taken.

> Why a bitmap allocator and not a heap allocator?

Because the allocator must be able to deal with small 4 byte entities.

> Also, looking at the lock usage, this thing is not IRQ safe, so it
> should not be called from hardirq context. Please document this.

Ok.
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