linux-kernel - Re: [patch] slab: Do not use mempolicy for kmalloc

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Date:	Wed, 13 Sep 2006 15:28:01 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Alok Kataria <alok.kataria@...softinc.com>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	Christoph Lameter <clameter@...r.sgi.com>,
	"Benzi Galili (Benzi@...leMP.com)" <benzi@...lemp.com>
Subject: Re: [patch] slab: Do not use mempolicy for kmalloc_node

I wish first of all that the description would accurately describe the 
problem.

On Wed, 13 Sep 2006, Ravikiran G Thirumalai wrote:

> +/* Allocate object from the array cache of the executing cpu */

I am not sure what this adds.

> +/* 
> + * Allocate object from the appropriate node as per mempolicy/cpuset
> + * constraints
> + */

We only do this under certain conditions. The main purpose of this 
function is to allocate an object without having specified a node.

>  	unsigned long save_flags;
>  	void *objp;
> -
>  	cache_alloc_debugcheck_before(cachep, flags);
> -
>  	local_irq_save(save_flags);

Extra material.

> +
> +#ifdef CONFIG_NUMA
> +	if (unlikely(current->flags & (PF_SPREAD_SLAB | PF_MEMPOLICY))) {
> +		objp = alternate_node_alloc(cachep, flags);
> +		if (objp != NULL) {
> +			local_irq_restore(save_flags);
> +			prefetchw(objp);
> +			return objp;
> +		}
> +	}
> +#endif
> +

Ok.

> @@ -3303,9 +3309,10 @@ void *kmem_cache_alloc_node(struct kmem_
>  	cache_alloc_debugcheck_before(cachep, flags);
>  	local_irq_save(save_flags);
>  
> -	if (nodeid == -1 || nodeid == numa_node_id() ||
> -			!cachep->nodelists[nodeid])
> +	if (nodeid == numa_node_id())
>  		ptr = ____cache_alloc(cachep, flags);
> +	else if (nodeid == -1 || !cachep->nodelists[nodeid])
> +		ptr = __cache_alloc(cachep, flags, __builtin_return_address(0));
>  	else

We are still allocating according to policy if nodeid == -1 or if we have 
an invalid node? I thought we agreed that kmalloc_node should never 
obey memory policies?

Simply move the #ifdef CONFIG_NUMA block as we agreed last night. And fix 
the description to specify under what conditions kmalloc_node will obey 
memory policies.
-
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