Subject: Re: slab: setup allocators earlier in the boot sequence
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Linux Kernel list <linux-kernel@vger.kernel.org>,
       linux-mm <linux-mm@kvack.org>, mingo@elte.hu, cl@linux-foundation.org,
       akpm@linux-foundation.org
In-Reply-To: <20090612075427.GA24044@wotan.suse.de>
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Date: Fri, 12 Jun 2009 10:59:52 +0300
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Hi Nick,

On Fri, Jun 12, 2009 at 10:45:45AM +0300, Pekka Enberg wrote:
> > On Fri, 2009-06-12 at 17:34 +1000, Benjamin Herrenschmidt wrote:
> > > I really believe this should be a slab internal thing, which is what my
> > > patch does to a certain extent. IE. All callers need to care about is
> > > KERNEL vs. ATOMIC and in some cases, NOIO or similar for filesystems
> > > etc... but I don't think all sorts of kernel subsystems, because they
> > > can be called early during boot, need to suddenly use GFP_NOWAIT all the
> > > time.
> > > 
> > > That's why I much prefer my approach :-) (In addition to the fact that
> > > it provides the basis for also fixing suspend/resume).
> > 
> > Sure, I think we can do what you want with the patch below.

On Fri, 2009-06-12 at 09:54 +0200, Nick Piggin wrote:
> I don't really like adding branches to slab allocator like this.
> init code all needs to know what services are available, and
> this includes the scheduler if it wants to do anything sleeping
> (including sleeping slab allocations).
> 
> Core mm code is the last place to put in workarounds for broken
> callers...

Yes, the initialization code can be fixed to use GFP_NOWAIT. But it's
really the suspend case that makes me think the patch might be a good
idea. So the patch does not attempt to be a workaround for buggy callers
but rather a change in policy that we simply refuse to wait during
bootup and suspend.

			Pekka

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