Re: [PATCH] slab: minor cleanup to kmem_cache_alloc_node

[Eric Dumazet <dada1@cosmosbay.com>]

Pekka J Enberg a écrit :
> This patch gets rid of one if-else statement by moving current node allocation
> check at the beginning of kmem_cache_alloc_node().
> 

Are you sure this is valid ?
What about preemption ?
The "if (nodeid == numa_node_id())" check was done with IRQ off, and you want 
do do it with IRQ on.

> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
> ---
> 
>  slab.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 7f80ec3..a05bbfe 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2881,7 +2881,7 @@ void *kmem_cache_alloc_node(kmem_cache_t
>  	unsigned long save_flags;
>  	void *ptr;
>  
> -	if (nodeid == -1)
> +	if (nodeid == -1 || nodeid == numa_node_id())

<Imagine preemption here, and thread migrated to another NUMA node.>

>  		return __cache_alloc(cachep, flags);
>  
>  	if (unlikely(!cachep->nodelists[nodeid])) {
> @@ -2892,10 +2892,7 @@ void *kmem_cache_alloc_node(kmem_cache_t
>  
>  	cache_alloc_debugcheck_before(cachep, flags);
>  	local_irq_save(save_flags);
> -	if (nodeid == numa_node_id())
> -		ptr = ____cache_alloc(cachep, flags);
> -	else
> -		ptr = __cache_alloc_node(cachep, flags, nodeid);
> +	ptr = __cache_alloc_node(cachep, flags, nodeid);
>  	local_irq_restore(save_flags);
>  	ptr = cache_alloc_debugcheck_after(cachep, flags, ptr, __builtin_return_address(0));
>