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

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Date:	Mon, 9 Feb 2009 00:43:19 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
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

On Mon, 9 Feb 2009 09:37:39 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> 
> * 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.

yup, something along those lines.

> 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.

Silent failure sounds bad?

The allocation attempt will spew a page-allocation-failure backtrace
anyway, so people will still get alarmed.

You might instead choose to suppress that warning with __GFP_NOWARN and
instead add a more meaningful warning at the calling codesite.


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