linux-kernel - Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

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Date:	Mon, 15 Jun 2009 10:55:47 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Pekka J Enberg <penberg@...helsinki.fi>
cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, kamezawa.hiroyu@...fujitsu.com,
	lizf@...fujitsu.com, mingo@...e.hu, npiggin@...e.de,
	yinghai@...nel.org, benh@...nel.crashing.org
Subject: Re: [GIT PULL v2] Early SLAB fixes for 2.6.31

On Sun, 14 Jun 2009, Pekka J Enberg wrote:

> How about something like this? There should be no extra code in fastpaths
> for production configs with this one.

Yes something like that would be good. More comments below.

> index 4d6004c..5e8cea1 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1613,6 +1613,8 @@ another_slab:
>  	deactivate_slab(s, c);
>
>  new_slab:
> +	gfpflags &= slab_gfp_mask;
> +

Move the processing of GFP_RECLAIM_MASK etc up to here from new_slab? Then
the flow is also more logical. The flags handling is concentrated in one
spot in the allocator and its more obvious how we handle gfp flags.

> @@ -1668,13 +1670,14 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
>  	struct kmem_cache_cpu *c;
>  	unsigned long flags;
>  	unsigned int objsize;
> +	gfp_t real_gfp;
>
> -	gfpflags &= slab_gfp_mask;
> +	real_gfp = gfpflags & slab_gfp_mask;
>
> -	lockdep_trace_alloc(gfpflags);
> -	might_sleep_if(gfpflags & __GFP_WAIT);
> +	lockdep_trace_alloc(real_gfp);
> +	might_sleep_if(real_gfp & __GFP_WAIT);
>
> -	if (should_failslab(s->objsize, gfpflags))
> +	if (should_failslab(s->objsize, real_gfp))
>  		return NULL;
>
>  	local_irq_save(flags);

Dont do it there. Only modify the slow path.

Look at __might_sleep(). It already has an exception for system_state !=
RUNNING. If it still triggers then add to the condition there.


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