Re: [RFC PATCH 2/3] sched/numa: Introduce per cgroup numa balance control

[Chen Yu]

On 2025-03-07 at 14:54:10 -0800, Tim Chen wrote:
> On Tue, 2025-02-25 at 22:00 +0800, Chen Yu wrote:
> > [Problem Statement]
> > Currently, NUMA balancing is configured system-wide. However,
> > 
> > 
> > A simple example to show how to use per-cgroup Numa balancing:
> > 
> > Step1
> > //switch to global per cgroup Numa balancing,
> > //All cgroup's Numa balance is disabled by default.
> > echo 4 > /proc/sys/kernel/numa_balancing
> > 
> 
> Can you add documentation of this additional feature
> for numa_balancing in
> admin-guide/sysctl/kernel.rst
>

OK, will refine in next version.
 
> Should you make NUMA_BALANCING_NORMAL and NUMA_BALANCING_CGROUP
> mutually exclusive in? In other words
> echo 5 > /proc/sys/kernel/numa_balancing should result in numa_balancing to be 1?
> 
> Otherwise tg_numa_balance_enabled() can return 0 with NUMA_BALANCING_CGROUP
> bit turned on even though you have NUMA_BALANCING_NORMAL bit on.
>

I see, will fix tg_numa_balance_enabled() in next version, thanks!

Best,
Chenyu
 
> Tim
> > 
> > Suggested-by: Tim Chen <tim.c.chen@xxxxxxxxx>
> > Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> > ---
> >  include/linux/sched/sysctl.h |  1 +
> >  kernel/sched/core.c          | 32 ++++++++++++++++++++++++++++++++
> >  kernel/sched/fair.c          | 18 ++++++++++++++++++
> >  kernel/sched/sched.h         |  3 +++
> >  mm/mprotect.c                |  5 +++--
> >  5 files changed, 57 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
> > index 5a64582b086b..1e4d5a9ddb26 100644
> > --- a/include/linux/sched/sysctl.h
> > +++ b/include/linux/sched/sysctl.h
> > @@ -22,6 +22,7 @@ enum sched_tunable_scaling {
> >  #define NUMA_BALANCING_DISABLED		0x0
> >  #define NUMA_BALANCING_NORMAL		0x1
> >  #define NUMA_BALANCING_MEMORY_TIERING	0x2
> > +#define NUMA_BALANCING_CGROUP		0x4
> >  
> >  #ifdef CONFIG_NUMA_BALANCING
> >  extern int sysctl_numa_balancing_mode;
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 44efc725054a..f4f048b3da68 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -10023,6 +10023,31 @@ static ssize_t cpu_max_write(struct kernfs_open_file *of,
> >  }
> >  #endif
> >  
> > +#ifdef CONFIG_NUMA_BALANCING
> > +static DEFINE_MUTEX(numa_balance_mutex);
> > +static int numa_balance_write_u64(struct cgroup_subsys_state *css,
> > +				  struct cftype *cftype, u64 enable)
> > +{
> > +	struct task_group *tg;
> > +	int ret;
> > +
> > +	guard(mutex)(&numa_balance_mutex);
> > +	tg = css_tg(css);
> > +	if (tg->nlb_enabled == enable)
> > +		return 0;
> > +
> > +	tg->nlb_enabled = enable;
> > +
> > +	return ret;
> > +}
> > +
> > +static u64 numa_balance_read_u64(struct cgroup_subsys_state *css,
> > +				 struct cftype *cft)
> > +{
> > +	return css_tg(css)->nlb_enabled;
> > +}
> > +#endif /* CONFIG_NUMA_BALANCING */
> > +
> >  static struct cftype cpu_files[] = {
> >  #ifdef CONFIG_GROUP_SCHED_WEIGHT
> >  	{
> > @@ -10071,6 +10096,13 @@ static struct cftype cpu_files[] = {
> >  		.seq_show = cpu_uclamp_max_show,
> >  		.write = cpu_uclamp_max_write,
> >  	},
> > +#endif
> > +#ifdef CONFIG_NUMA_BALANCING
> > +	{
> > +		.name = "numa_load_balance",
> > +		.read_u64 = numa_balance_read_u64,
> > +		.write_u64 = numa_balance_write_u64,
> > +	},
> >  #endif
> >  	{ }	/* terminate */
> >  };
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1c0ef435a7aa..526cb33b007c 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3146,6 +3146,18 @@ void task_numa_free(struct task_struct *p, bool final)
> >  	}
> >  }
> >  
> > +/* return true if the task group has enabled the numa balance */
> > +static bool tg_numa_balance_enabled(struct task_struct *p)
> > +{
> > +	struct task_group *tg = task_group(p);
> > +
> > +	if (tg && (sysctl_numa_balancing_mode & NUMA_BALANCING_CGROUP) &&
> > +	    !tg->nlb_enabled)
> > +		return false;
> > +
> > +	return true;
> > +}
> > +
> >  /*
> >   * Got a PROT_NONE fault for a page on @node.
> >   */
> > @@ -3174,6 +3186,9 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
> >  	     !cpupid_valid(last_cpupid)))
> >  		return;
> >  
> > +	if (!tg_numa_balance_enabled(p))
> > +		return;
> > +
> >  	/* Allocate buffer to track faults on a per-node basis */
> >  	if (unlikely(!p->numa_faults)) {
> >  		int size = sizeof(*p->numa_faults) *
> > @@ -3596,6 +3611,9 @@ static void task_tick_numa(struct rq *rq, struct task_struct *curr)
> >  	if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work)
> >  		return;
> >  
> > +	if (!tg_numa_balance_enabled(curr))
> > +		return;
> > +
> >  	/*
> >  	 * Using runtime rather than walltime has the dual advantage that
> >  	 * we (mostly) drive the selection from busy threads and that the
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 38e0e323dda2..9f478fb2c03a 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -491,6 +491,9 @@ struct task_group {
> >  	/* Effective clamp values used for a task group */
> >  	struct uclamp_se	uclamp[UCLAMP_CNT];
> >  #endif
> > +#ifdef CONFIG_NUMA_BALANCING
> > +	u64			nlb_enabled;
> > +#endif
> >  
> >  };
> >  
> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index 516b1d847e2c..ddaaf20ef94c 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -155,10 +155,11 @@ static long change_pte_range(struct mmu_gather *tlb,
> >  				toptier = node_is_toptier(nid);
> >  
> >  				/*
> > -				 * Skip scanning top tier node if normal numa
> > +				 * Skip scanning top tier node if normal/cgroup numa
> >  				 * balancing is disabled
> >  				 */
> > -				if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
> > +				if (!(sysctl_numa_balancing_mode &
> > +				    (NUMA_BALANCING_CGROUP | NUMA_BALANCING_NORMAL)) &&
> >  				    toptier)
> >  					continue;
> >  				if (folio_use_access_time(folio))
>