On 11.07.2014 [15:37:34 +0800], Jiang Liu wrote: > When CONFIG_HAVE_MEMORYLESS_NODES is enabled, cpu_to_node()/numa_node_id() > may return a node without memory, and later cause system failure/panic > when calling kmalloc_node() and friends with returned node id. > So use cpu_to_mem()/numa_mem_id() instead to get the nearest node with > memory for the/current cpu. You used the same changelog for all of the patches, it seems. But the interface below (kthread_create_on_node) doesn't go into kmalloc_node? kthread_create_on_node eventually sets the value used by tsk_fork_get_node(), which is used by alloc_task_struct_node() and alloc_thread_info_node(). The first uses kmem_cache_alloc_node() and the second, depending on the relative sizes of THREAD_SIZE and PAGE_SIZE uses either alloc_kmem_pages_node() or kmem_cache_alloc_node(). kmem_cache_alloc_node() goes into the appropriate slab allocator which on SLUB for instance, goes down into __alloc_pages_nodemask. But no failure occurs when memoryless nodes are present, you just get memory that is remote from the node specified? Similarly, alloc_kmem_pages_node() calls into __alloc_pages with an appropriate node_zonelist, which should provide for the correct fallback based upon NUMA topology? What system failure/panic did you see that is resolved by this patch? > If CONFIG_HAVE_MEMORYLESS_NODES is disabled, cpu_to_mem()/numa_mem_id() > is the same as cpu_to_node()/numa_node_id(). > > Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx> > --- > drivers/thermal/intel_powerclamp.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c > index 95cb7fc20e17..9d9be8cd1b50 100644 > --- a/drivers/thermal/intel_powerclamp.c > +++ b/drivers/thermal/intel_powerclamp.c > @@ -531,7 +531,7 @@ static int start_power_clamp(void) > > thread = kthread_create_on_node(clamp_thread, > (void *) cpu, > - cpu_to_node(cpu), > + cpu_to_mem(cpu), As Tejun has pointed out elsewhere, we lose context here about the original node we were running on. That information is relevant for a few reasons: 1) In the underlying allocator, we might not have memory *right now* to satisfy a request, which, say, causes us to deactivate a slab (CONFIG_SLUB). But that condition may be relieved in the future and we want to use the correct node again then. 2) For topologies that are symmetrical around a memoryless node, we could lose the correct fallback information when we specify a nearest neighbor with memory. Thanks, Nish -- To unsubscribe from this list: send the line "unsubscribe linux-hotplug" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
