Re: [Patch: 003/006] pgdat allocation for new node add (generic alloc node_data)

Andrew Morton
2006-04-20T23:02:46Z

Yasunori Goto <y-goto@jp.fujitsu.com> wrote:
>
> +#define generic_alloc_nodedata(nid) \
> +({ \
> + (pg_data_t *)kzalloc(sizeof(pg_data_t), GFP_KERNEL); \
> +})

In general, library functions which perform memory allocation should not
make assumptions about which gfp_t they are allowed to use.

So this really should be `generic_alloc_nodedata(nid, gfp_mask)'.

However, it's very desirable that memory allocations use GFP_KERNEL rather
than, say, GFP_ATOMIC. So your interface here _forces_ callers to be in a
state where GFP_KERNEL is legal, which is good discipline.

Although if that turns out to be a problem, we can expect to see a sad
little patch from someone which tries to change this to GFP_ATOMIC, which
makes everything worse - even those callers who _can_ use GFP_KERNEL.

(In practice, NUMA developers seem to never test with sufficient
CONFIG_DEBUG_* flags enabled, and with CONFIG_PREEMPT, so they happily
don't get to discover their sleep-in-spinlock bugs anyway).

Anyway, on balance, I think it'd be best to convert this API to take a
gfp_t as well.