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

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Date:	Fri, 12 Jun 2009 09:54:27 +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 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.

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...

> 
> But I still think we need my patch regardless. The call sites I
> converted are all init code and should be using GFP_NOWAIT. Does it fix
> your boot on powerpc?
> 
> 			Pekka
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 9a90b00..722beb5 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2791,6 +2791,13 @@ static int cache_grow(struct kmem_cache *cachep,
>  
>  	offset *= cachep->colour_off;
>  
> +	/*
> +	 * Lets not wait if we're booting up or suspending even if the user
> +	 * asks for it.
> +	 */
> +	if (system_state != SYSTEM_RUNNING)
> +		local_flags &= ~__GFP_WAIT;
> +
>  	if (local_flags & __GFP_WAIT)
>  		local_irq_enable();
>  
> diff --git a/mm/slub.c b/mm/slub.c
> index 65ffda5..f9a6bc8 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1547,6 +1547,13 @@ new_slab:
>  		goto load_freelist;
>  	}
>  
> +	/*
> +	 * Lets not wait if we're booting up or suspending even if the user
> +	 * asks for it.
> +	 */
> +	if (system_state != SYSTEM_RUNNING)
> +		gfpflags &= ~__GFP_WAIT;
> +
>  	if (gfpflags & __GFP_WAIT)
>  		local_irq_enable();
>  
> 
--
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