on 2010-2-24 6:31, David Rientjes wrote: > On Tue, 23 Feb 2010, Miao Xie wrote: > >>> Cpu hotplug sets top_cpuset's cpus_allowed to cpu_active_mask by default, >>> regardless of what was onlined or offlined. cpus_attach in the context of >>> your patch (in cpuset_attach()) passes cpu_possible_mask to >>> set_cpus_allowed_ptr() if the task is being attached to top_cpuset, my >>> question was why don't we pass cpu_active_mask instead? In other words, I >>> think we should do >>> >>> cpumask_copy(cpus_attach, cpu_active_mask); >>> >>> when attached to top_cpuset like my patch did. >> >> If we pass cpu_active_mask to set_cpus_allowed_ptr(), task->cpus_allowed just contains >> the online cpus. In this way, if we do cpu hotplug(such as: online some cpu), we must >> update cpus_allowed of all tasks in the top cpuset. >> >> But if we pass cpu_possible_mask, we needn't update cpus_allowed of all tasks in the >> top cpuset. And when the kernel looks for a cpu for task to run, the kernel will use >> cpu_active_mask to filter out offline cpus in task->cpus_allowed. Thus, it is safe. >> > > That is terribly inconsistent between top_cpuset and all descendants; all > other cpusets require that task->cpus_allowed be a subset of > cpu_online_mask, including those descendants that allow all cpus (and all > mems). I think it is not a big deal because it is safe and doesn't cause any problem. Beside that, task->cpus_allowed is initialized to cpu_possible_mask on the no-cpuset kernel, so using cpu_possible_mask to initialize task->cpus_allowed is reasonable. (top cpuset is a special cpuset, isn't it?) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>