[PATCH] mm: rename and document alloc_pages_exact_node

[Michael Ellerman]

On Tue, 2015-07-21 at 15:55 +0200, Vlastimil Babka wrote:
> The function alloc_pages_exact_node() was introduced in 6484eb3e2a81 ("page
> allocator: do not check NUMA node ID when the caller knows the node is valid")
> as an optimized variant of alloc_pages_node(), that doesn't allow the node id
> to be -1. Unfortunately the name of the function can easily suggest that the
> allocation is restricted to the given node. In truth, the node is only
> preferred, unless __GFP_THISNODE is among the gfp flags.
> 
> The misleading name has lead to mistakes in the past, see 5265047ac301 ("mm,
> thp: really limit transparent hugepage allocation to local node") and
> b360edb43f8e ("mm, mempolicy: migrate_to_node should only migrate to node").
> 
> To prevent further mistakes, this patch renames the function to
> alloc_pages_prefer_node() and documents it together with alloc_pages_node().
> 
> Signed-off-by: Vlastimil Babka <vbabka at suse.cz>
 
>  I'm CC'ing also maintainers of the callsites so they can verify that the
>  callsites that don't pass __GFP_THISNODE are really not intended to restrict
>  allocation to the given node. I went through them myself and each looked like
>  it's better off if it can successfully allocate on a fallback node rather
>  than fail. DavidR checked them also I think, but it's better if maintainers
>  can verify that. I'm not completely sure about all the usages in sl*b due to
>  multiple layers through which gfp flags are being passed.


> diff --git a/arch/powerpc/platforms/cell/ras.c b/arch/powerpc/platforms/cell/ras.c
> index e865d74..646a310 100644
> --- a/arch/powerpc/platforms/cell/ras.c
> +++ b/arch/powerpc/platforms/cell/ras.c
> @@ -123,7 +123,7 @@ static int __init cbe_ptcal_enable_on_node(int nid, int order)
>  
>  	area->nid = nid;
>  	area->order = order;
> -	area->pages = alloc_pages_exact_node(area->nid,
> +	area->pages = alloc_pages_prefer_node(area->nid,
>  						GFP_KERNEL|__GFP_THISNODE,
>  						area->order);

Yeah that looks right to me.

This code enables some firmware memory calibration so I think it really does
want to get memory on the specified node, or else fail.

Acked-by: Michael Ellerman <mpe at ellerman.id.au>

cheers