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

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Date:	Fri, 12 Jun 2009 17:39:40 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Pekka J Enberg <penberg@...helsinki.fi>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, mingo@...e.hu
Subject: Re: slab: setup allocators earlier in the boot sequence

On Fri, 2009-06-12 at 17:34 +1000, Benjamin Herrenschmidt wrote:

> I don't like that approach at all. Fixing all the call sites... we are
> changing things all over the place, we'll certainly miss some, and
> honestly, it's none of the business of things like vmalloc to know about
> things like what kmalloc flags are valid and when... 

Oh and btw, your patch alone doesn't fix powerpc, because it's missing
a whole bunch of GFP_KERNEL's in the arch code... You would have to
grep the entire kernel for things that check slab_is_available() and
even then you'll be missing some.

For example, slab_is_available() didn't always exist, and so in the
early days on powerpc, we used a mem_init_done global that is set form
mem_init() (not perfect but works in practice). And we still have code
using that to do the test.

Anyway, I think changing all the call sites is the wrong approach,
especially for things that can routinely be called after boot when
GFP_KERNEL is the right thing to do.

Cheers,
Ben.

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