linux-kernel - Re: [PATCH v2] slab,slub: ignore __GFP_WAIT if we're booting or suspending

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Date:	Fri, 12 Jun 2009 12:15:11 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, benh@...nel.crashing.org,
	akpm@...ux-foundation.org, cl@...ux-foundation.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH v2] slab,slub: ignore __GFP_WAIT if we're booting or suspending

On Fri, Jun 12, 2009 at 01:11:52PM +0300, Pekka Enberg wrote:
> Hi Ingo,
> 
> On Fri, Jun 12, 2009 at 1:07 PM, Ingo Molnar<mingo@...e.hu> wrote:
> > IMHO such invisible side-channels modifying the semantics of GFP
> > flags is a bit dubious.
> >
> > We could do GFP_INIT or GFP_BOOT. These can imply other useful
> > modifiers as well: panic-on-failure for example. (this would clean
> > up a fair amount of init code that currently checks for an panics on
> > allocation failure.)
> 
> OK, but that means we need to fix up every single caller. I'm fine
> with that but Ben is not. As I am unable to test powerpc here, I am
> inclined to just merge Ben's patch as "obviously correct".

I agree with Ingo though that exposing it as a gfp modifier is
not so good. I just like the implementation to mask off GFP_WAIT
better, and also prefer not to test system state, but have someone
just call into slab to tell it not to unconditionally enable
interrupts.

> That does not mean we can't introduce GFP_BOOT later on if we want to. Hmm?

Yes, with sufficient warnings in place, I don't think it should be
too error prone to clean up remaining code over the course of
a few releases.

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