On 2014/7/22 1:47, Nishanth Aravamudan wrote:
> On 11.07.2014 [15:37:45 +0800], Jiang Liu wrote:
>> Current kernel only updates _mem_id_[cpu] for onlined CPUs when memory
>> configuration changes. So kernel may allocate memory from remote node
>> for a CPU if the CPU is still in absent or offline state even if the
>> node associated with the CPU has already been onlined.
>
> This just sounds like the topology information is being updated at the
> wrong place/time? That is, the memory is online, the CPU is being
> brought online, but isn't associated with any node?
Hi Nishanth,
Yes, that's the case.
>
>> This patch tries to improve performance by updating _mem_id_[cpu] for
>> each possible CPU when memory configuration changes, thus kernel could
>> always allocate from local node once the node is onlined.
>
> Ok, what is the impact? Do you actually see better performance?
No real data to support this yet, just with code analysis.
Regards!
Gerry
>
>> We check node_online(cpu_to_node(cpu)) because:
>> 1) local_memory_node(nid) needs to access NODE_DATA(nid)
>> 2) try_offline_node(nid) just zeroes out NODE_DATA(nid) instead of free it
>>
>> Signed-off-by: Jiang Liu <jiang....@linux.intel.com>
>> ---
>> mm/page_alloc.c | 10 +++++-----
>> 1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 0ea758b898fd..de86e941ed57 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3844,13 +3844,13 @@ static int __build_all_zonelists(void *data)
>> /*
>> * We now know the "local memory node" for each node--
>> * i.e., the node of the first zone in the generic zonelist.
>> - * Set up numa_mem percpu variable for on-line cpus. During
>> - * boot, only the boot cpu should be on-line; we'll init the
>> - * secondary cpus' numa_mem as they come on-line. During
>> - * node/memory hotplug, we'll fixup all on-line cpus.
>> + * Set up numa_mem percpu variable for all possible cpus
>> + * if associated node has been onlined.
>> */
>> - if (cpu_online(cpu))
>> + if (node_online(cpu_to_node(cpu)))
>> set_cpu_numa_mem(cpu,
>> local_memory_node(cpu_to_node(cpu)));
>> + else
>> + set_cpu_numa_mem(cpu, NUMA_NO_NODE);
>> #endif
>
>
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