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SubjectRe: [PATCH] irq: optimize init_kstat_irqs/init_copy_kstat_irqs
On Mon, 9 Feb 2009 09:37:39 +0100 Ingo Molnar <mingo@elte.hu> wrote:

>
> * Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Mon, 9 Feb 2009 09:11:24 +0100 Ingo Molnar <mingo@elte.hu> wrote:
> >
> > >
> > > * Andrew Morton <akpm@linux-foundation.org> wrote:
> > >
> > > > On Sat, 7 Feb 2009 01:01:03 -0800 Yinghai Lu <yinghai@kernel.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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