linux-kernel - Re: [PATCH] irq: optimize init_kstat_irqs/init_copy_kstat

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Message-ID: <20090209083739.GB15517@elte.hu>
Date:	Mon, 9 Feb 2009 09:37:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Yinghai Lu <yinghai@...nel.org>, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq: optimize init_kstat_irqs/init_copy_kstat_irqs


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 9 Feb 2009 09:11:24 +0100 Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Andrew Morton <akpm@...ux-foundation.org> wrote:
> > 
> > > On Sat, 7 Feb 2009 01:01:03 -0800 Yinghai Lu <yinghai@...nel.org> wrote:
> > > 
> > > > 
> > > > add kzalloc_node_safe()?
> > > 
> > > I cannot find that function.
> > 
> > His suggestion is to provide that allocator variant.
> > 
> 
> Oh.
> 
> It isn't possible to write a kzalloc_node_safe(GFP_ATOMIC).  Or at
> least, we've never worked out a way.
> 
> Maybe I'm confused again.

Indeed - duh - more morning tea needed.

Yinghai, why are those allocations GFP_ATOMIC to begin with? These:

earth4:~/tip> grep GFP_ATOMIC kernel/irq/*.c
kernel/irq/handle.c:	ptr = kzalloc_node(nr * sizeof(*desc->kstat_irqs), GFP_ATOMIC, node);
kernel/irq/handle.c:	desc = kzalloc_node(sizeof(*desc), GFP_ATOMIC, node);
kernel/irq/manage.c:	action = kmalloc(sizeof(struct irqaction), GFP_ATOMIC);

Should all be GFP_KERNEL. Wherever they are within a spinlocked section the code 
should be restructured. All descriptor data structures should be preallocated at 
__setup_irq() time. If we ever need to allocate dynamically later on, in the middle 
of some difficult codepath that's a structure bug in the code.

and this one:

kernel/irq/numa_migrate.c:	desc = kzalloc_node(sizeof(*desc), GFP_ATOMIC, node);

should fail the migration silently if GFP_ATOMIC returns NULL.

	Ingo
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