Re: [PATCH] mm: rename and document alloc_pages_exact_node

Michael Ellerman
2015-07-22T01:23:00Z

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@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@ellerman.id.au>

cheers