linux-kernel - Re: [PATCH -mm] slub: update cpu after new

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Message-ID: <Pine.LNX.4.64.0704250857170.24530@schroedinger.engr.sgi.com>
Date:	Wed, 25 Apr 2007 08:58:53 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Hugh Dickins <hugh@...itas.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] slub: update cpu after new_slab()

On Wed, 25 Apr 2007, Hugh Dickins wrote:

> > Right. local_irq_save does not switch off preemption as I thought.
> 
> Strange comment.  Preemption is not possible while IRQs are disabled,
> but new_slab() rightly reenables them within itself in the __GFP_WAIT
> case, since it's going off to do a page allocation and may need to wait.

Yes I expected local_irq_save to increase the preempt count and then 
local_irq_enable to simply enable interrupts without affecting the preempt 
count. Thus the process should stay on the same processor.

Never thought it would be possible to move to a different processor in mid 
flight.
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