linux-kernel - Re: slab: setup allocators earlier in the boot sequence

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Date:	Fri, 12 Jun 2009 11:13:04 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, mingo@...e.hu,
	cl@...ux-foundation.org, akpm@...ux-foundation.org
Subject: Re: slab: setup allocators earlier in the boot sequence

On Fri, Jun 12, 2009 at 11:49:31AM +0300, Pekka Enberg wrote:
> On Fri, Jun 12, 2009 at 11:44 AM, Benjamin
> Herrenschmidt<benh@...nel.crashing.org> wrote:
> > On Fri, 2009-06-12 at 11:04 +0300, Pekka Enberg wrote:
> >> Hi Nick,
> >>
> >> On Fri, 2009-06-12 at 10:02 +0200, Nick Piggin wrote:
> >> > Fair enough, but this can be done right down in the synchronous
> >> > reclaim path in the page allocator. This will catch more cases
> >> > of code using the page allocator directly, and should be not
> >> > as hot as the slab allocator.
> >>
> >> So you want to push the local_irq_enable() to the page allocator too? We
> >> can certainly do that but I think we ought to wait for Andrew to merge
> >> Mel's patches to mainline first, OK?
> >
> > Doesn't my patch take care of all the cases in a much more simple way ?
> 
> Nick, the patch Ben is talking about is here:
> 
> http://patchwork.kernel.org/patch/29700/

It's OK. I'd make it gfp_notsmellybits, and avoid the ~.
And read_mostly.
 
> The biggest problem with the patch is that the gfp_smellybits is wide
> open for abuse. Hmm.

Probably would be better to hide it in mm/ and then just
allow it to be modified with a couple of calls. OTOH if
it is only modified in a couple of places then maybe that's
overkill.

The whole problem comes about because we don't just restore
our previously saved flags here... I guess it probably adds
even more overhead to do that and make everything just work :(


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