On Wed, 13 Sep 2006, Ravikiran G Thirumalai wrote:
> > We only do this under certain conditions. The main purpose of this
> > function is to allocate an object without having specified a node.
>
> Yes, the conditions being cpuset constraints or a mempolicy being in place.
> Again, since objects can be allocated off other nodes under certain
> conditions, I thought it was good to document it...
This is only true for the CONFIG_NUMA case.
> This is the case when we are requesting an object from a non existent
> node/invalid node. So we have 2 choices, either to spread the allocations
> as per the cpuset constraints (the same treatment as kmalloc), or to
> allocate from the requesting node, either ways we are not strictly
> confirming to the user's choice of node (which we cannot). I cannot see
> major advantage or disadvantage either ways, so I chose to keep the policy
> in current mainline code -- spread according to the policy set.
The two cases were your patch still applied memory policies were:
1. nodeid = -1. This is one particular case that we wanted to fix because
it means use numa_node_id().
2. The case where the nodelist does not yet exist.
AFAIK this situation only occurs on boot strap when we are actually
attempting to allocate from a different node than what we are running on.
Falling back to the local node is the right thing to do because we have
that already working. A process that is running on a node must always have
the nodelists for all caches allocated. The cpuup callbacks take care of that.
kmalloc_node needs work like page_alloc_node. page_alloc_node() never
consults memory policies and thus one would not expect kmalloc_node to do
so either.
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