Re: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas

Tejun Heo
2009-09-22T00:02:39Z

Hello,

Mel Gorman wrote:
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 1f68160..a5f52d4 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -588,6 +588,26 @@ void __init setup_per_cpu_areas(void)
> paca[i].data_offset = ptr - __per_cpu_start;
> memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
> }
> +#ifdef CONFIG_SLQB
> + /*
> + * SLQB abuses DEFINE_PER_CPU to setup a per-node area. This trick
> + * assumes that ever node ID will have a CPU of that ID to match.
> + * On systems with memoryless nodes, this may not hold true. Hence,
> + * we take a second pass initialising a "per-cpu" area for node-ids
> + * that SLQB can use
> + */
> + for_each_node_state(i, N_NORMAL_MEMORY) {
> +
> + /* Skip node IDs that a valid CPU id exists for */
> + if (paca[i].data_offset)
> + continue;
> +
> + ptr = alloc_bootmem_pages_node(NODE_DATA(cpu_to_node(i)), size);
> +
> + paca[i].data_offset = ptr - __per_cpu_start;
> + memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
> + }
> +#endif /* CONFIG_SLQB */
> }
> #endif

Eh... I don't know. This seems too hacky to me. Why not just
allocate pointer array of MAX_NUMNODES and allocate per-node memory
there? This will be slightly more expensive but I doubt it will be
noticeable. The only extra overhead is the cachline footprint for the
extra array.

Thanks.

--
tejun