linux-kernel - Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

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Message-ID: <20090617161744.GA22192@wotan.suse.de>
Date:	Wed, 17 Jun 2009 18:17:44 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	cl@...ux-foundation.org, kamezawa.hiroyu@...fujitsu.com,
	lizf@...fujitsu.com, mingo@...e.hu, yinghai@...nel.org
Subject: Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

On Wed, Jun 17, 2009 at 09:01:16AM -0700, Linus Torvalds wrote:
> 
> 
> On Wed, 17 Jun 2009, Nick Piggin wrote:
> > 
> > In some cases perhaps it is difficult. In others it should be
> > pretty natural. Lots of memory allocating paths pass gfp
> > a long way down the stack.
> 
> I agree that some cases would be pretty natural. In fact, that's what we 
> started out doing. On the x86 side, we didn't have a lot of issues in 
> testing, and we fixed them up by using GFP_NOWAIT (see for example 
> cpupri_init() in kernel/sched_cpupri.c, or init_irq_default_affinity() in 
> kernel/irq/handle.c - both of which were fixed up in that phase).
> 
> Those paths, in fact, in general already had "bootmem" flags etc. And x86 
> doesn't need to initialize a lot of state at bootup. 

Yes.

 
> Then Ben happened, and crazy PPC ioremap crap. 

OK. I agree ioremap probably would get painful. Are they doing that
too early anyway? From your email it sounds like maybe they are.

 
> So the problem is exactly that it was perfectly natural to pass down a gfp 
> or other flag in _some_ cases. And then in a few cases it's much more 
> painful.

Sure... I understand, and I don't want to force people to add
more nasty code to work around these. I am fine with the fix
to slab for now... I was just hoping maybe we don't put the
rule in place that all early boot allocations shall use GFP_KERNEL.
I'd like to see the allocation context passed down (including via
code that knows when interrupts are off in early boot) if possible
without ttoo much ugliness.

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