Commit d8b163c4 authored Nov 11, 2014 by Kirill Tkhai Committed by Ingo Molnar Nov 16, 2014

sched/numa: Init numa balancing fields of init_task



We do not initialize init_task.numa_preferred_nid,
but this value is inherited by userspace "init"
process:

rest_init()->kernel_thread(kernel_init)->do_fork(CLONE_VM);

__sched_fork()
{
	if (clone_flags & CLONE_VM)
		p->numa_preferred_nid = current->numa_preferred_nid;
	else
		p->numa_preferred_nid = -1;
}

kernel_init() becomes userspace "init" process.

So, we propagate garbage nid to userspace, and it may be used
during numa balancing.

Currently, we do not have reports about this brings a problem,
but it seem we should set it for sure.

Even if init_task.numa_preferred_nid is zero, we may meet a weird
configuration without nid#0. On sparc64, where processors are
numbered physically, I saw a machine without cpu#1, while cpu#2
existed. Possible, something similar may be with numa nodes.
So, let's initialize it and be sure we're safe.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Eric Paris <eparis@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Sergey Dyasly <dserrg@gmail.com>
Link: http://lkml.kernel.org/r/1415699189.15631.6.camel@tkhai


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent c1a2b5f6

include/linux/init_task.h

+10 −0

Original line number	Diff line number	Diff line
		@@ -166,6 +166,15 @@ extern struct task_group root_task_group;
		# define INIT_RT_MUTEXES(tsk)
		#endif

		#ifdef CONFIG_NUMA_BALANCING
		# define INIT_NUMA_BALANCING(tsk) \
		.numa_preferred_nid = -1, \
		.numa_group = NULL, \
		.numa_faults = NULL,
		#else
		# define INIT_NUMA_BALANCING(tsk)
		#endif

		/*
		* INIT_TASK is used to set up the first task table, touch at
		* your own risk!. Base=0, limit=0x1fffff (=2MB)
		@@ -237,6 +246,7 @@ extern struct task_group root_task_group;
		INIT_CPUSET_SEQ(tsk) \
		INIT_RT_MUTEXES(tsk) \
		INIT_VTIME(tsk) \
		INIT_NUMA_BALANCING(tsk) \
		}

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