linux-kernel - Re: [Bug #14467] Linker errors on ia64 with NR

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Message-ID: <4AE9B090.9090107@kernel.org>
Date:	Thu, 29 Oct 2009 16:11:12 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Jiri Kosina <jkosina@...e.cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Jeff Mahoney <jeffm@...e.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [Bug #14467] Linker errors on ia64 with NR_CPUS=4096

Christoph Lameter wrote:
> On Thu, 29 Oct 2009, Tejun Heo wrote:
> 
>> It's just for sched_init() which has irq off but is not really in
>> atomic context and does GFP_KERNEL allocations.  The following comment
>> has been added to the first patch to explain it.
> 
> Uhmm.. Is the page allocator available at that point? If you are
> constricted to the reserved per cpu area then IA64 can still run out of
> space if its booted with 4096 actual cpus.

sched_init() is after mm_init() so it should work.

>> + * allocations are done using GFP_KERNEL with pcpu_lock released.  In
>> + * general, percpu memory can't be allocated with irq off but
>> + * irqsave/restore are still used in alloc path so that it can be used
>> + * from early init path - sched_init() specifically.
> 
> Maybe make the patch a bit more general so that it can operate in an
> atomic context and handles gfp flags nicely?

That would be nice but currently, we have no user which needs anything
other than GFP_KERNEL although lack of users could have been caused by
the lack of the functionality and the non-atomic irq disabled state is
an exception case which is handled differently by might_sleep() too.
So, I'm not sure whether adding GFP_* parameter would worth the
effort.  Also, adding that is a bit too late for 2.6.32 at this point.

Thanks.

-- 
tejun
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