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.liu@xxxxxxxxxxxxxxx> >> --- >> 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 > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>