Re: [PATCH 3/8] sched: Select a preferred node with the most numa hinting faults

[Mel Gorman <mgorman@suse.de>]

On Fri, Jun 28, 2013 at 11:44:28AM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@suse.de> [2013-06-26 15:38:02]:
> 
> > This patch selects a preferred node for a task to run on based on the
> > NUMA hinting faults. This information is later used to migrate tasks
> > towards the node during balancing.
> > 
> > Signed-off-by: Mel Gorman <mgorman@suse.de>
> > ---
> >  include/linux/sched.h |  1 +
> >  kernel/sched/core.c   | 10 ++++++++++
> >  kernel/sched/fair.c   | 16 ++++++++++++++--
> >  kernel/sched/sched.h  |  2 +-
> >  4 files changed, 26 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 72861b4..ba46a64 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1507,6 +1507,7 @@ struct task_struct {
> >  	struct callback_head numa_work;
> >  
> >  	unsigned long *numa_faults;
> > +	int numa_preferred_nid;
> >  #endif /* CONFIG_NUMA_BALANCING */
> >  
> >  	struct rcu_head rcu;
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index f332ec0..019baae 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1593,6 +1593,7 @@ static void __sched_fork(struct task_struct *p)
> >  	p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0;
> >  	p->numa_migrate_seq = p->mm ? p->mm->numa_scan_seq - 1 : 0;
> >  	p->numa_scan_period = sysctl_numa_balancing_scan_delay;
> > +	p->numa_preferred_nid = -1;
> 
> Though we may not want to inherit faults, I think the tasks generally
> share pages with their siblings, parent. So will it make sense to
> inherit the preferred node?
> 

If it really shared data with its parent then it will be detected by the PTE
scanner later as normal. I would expect that initially it would be scheduled
to run on CPUs on the local node and I would think that inheriting it here
will not make a detectable difference. If you think it will, I can do it
but then the data should certainly be cleared on exec.

-- 
Mel Gorman
SUSE Labs