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

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Date:	Fri, 12 Jun 2009 19:24:20 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	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


> It's OK. I'd make it gfp_notsmellybits, and avoid the ~.
> And read_mostly.

read_mostly is fine. gfp_notsmellybits isn't a nice name :-) Make it
gfp_allowedbits then. I did it backward on purpose though as the risk of
"missing" bits here (as we may add new ones) is higher and it seemed to
me generally simpler to just explicit spell out the ones to forbid
(also, on powerpc,  &~ is one instruction :-)
 
> 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.

It might indeed be nicer to hide it behind an accessor.

> 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 :(

Well... that's part of the equation. My solution has the advantage to
also providing ground to forbid GFP_IO during suspend/resume etc...

Cheers,
Ben.

> 
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