Re: [RFC][PATCH 4/4] Memory controller soft limit reclaim on contention (v2)

[KOSAKI Motohiro]

> 
> From: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> 
> Changelog v2...v1
> 1. Added support for hierarchical soft limits
> 
> This patch allows reclaim from memory cgroups on contention (via the
> __alloc_pages_internal() path). If a order greater than 0 is specified, we
> anyway fall back on try_to_free_pages().
> 
> memory cgroup soft limit reclaim finds the group that exceeds its soft limit
> by the largest amount and reclaims pages from it and then reinserts the
> cgroup into its correct place in the rbtree.
> 
> Signed-off-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> ---
> 
>  include/linux/memcontrol.h |    1 
>  mm/memcontrol.c            |  105 +++++++++++++++++++++++++++++++++++++++-----
>  mm/page_alloc.c            |   10 ++++
>  3 files changed, 104 insertions(+), 12 deletions(-)
> 
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 18146c9..a50f73e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -116,6 +116,7 @@ static inline bool mem_cgroup_disabled(void)
>  }
>  
>  extern bool mem_cgroup_oom_called(struct task_struct *task);
> +extern unsigned long mem_cgroup_soft_limit_reclaim(gfp_t gfp_mask);
>  
>  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
>  struct mem_cgroup;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a2617ac..dd835d3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -188,6 +188,7 @@ struct mem_cgroup {
>  	struct rb_node mem_cgroup_node;
>  	unsigned long long usage_in_excess;
>  	unsigned long last_tree_update;
> +	bool on_tree;
>  
>  	/*
>  	 * statistics. This must be placed at the end of memcg.
> @@ -195,7 +196,7 @@ struct mem_cgroup {
>  	struct mem_cgroup_stat stat;
>  };
>  
> -#define	MEM_CGROUP_TREE_UPDATE_INTERVAL		(HZ)
> +#define	MEM_CGROUP_TREE_UPDATE_INTERVAL		(HZ/4)

??
moving [3/4] is proper more?


>  
>  enum charge_type {
>  	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
> @@ -229,14 +230,15 @@ static void mem_cgroup_get(struct mem_cgroup *mem);
>  static void mem_cgroup_put(struct mem_cgroup *mem);
>  static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
>  
> -static void mem_cgroup_insert_exceeded(struct mem_cgroup *mem)
> +static void __mem_cgroup_insert_exceeded(struct mem_cgroup *mem)
>  {
>  	struct rb_node **p = &mem_cgroup_soft_limit_exceeded_groups.rb_node;
>  	struct rb_node *parent = NULL;
>  	struct mem_cgroup *mem_node;
> -	unsigned long flags;
>  
> -	spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> +	if (mem->on_tree)
> +		return;
> +
>  	while (*p) {
>  		parent = *p;
>  		mem_node = rb_entry(parent, struct mem_cgroup, mem_cgroup_node);
> @@ -253,6 +255,23 @@ static void mem_cgroup_insert_exceeded(struct mem_cgroup *mem)
>  	rb_insert_color(&mem->mem_cgroup_node,
>  			&mem_cgroup_soft_limit_exceeded_groups);
>  	mem->last_tree_update = jiffies;
> +	mem->on_tree = true;
> +}
> +
> +static void __mem_cgroup_remove_exceeded(struct mem_cgroup *mem)
> +{
> +	if (!mem->on_tree)
> +		return;
> +	rb_erase(&mem->mem_cgroup_node, &mem_cgroup_soft_limit_exceeded_groups);
> +	mem->on_tree = false;
> +}
> +
> +static void mem_cgroup_insert_exceeded(struct mem_cgroup *mem)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> +	__mem_cgroup_insert_exceeded(mem);
>  	spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
>  }
>  
> @@ -260,10 +279,34 @@ static void mem_cgroup_remove_exceeded(struct mem_cgroup *mem)
>  {
>  	unsigned long flags;
>  	spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> -	rb_erase(&mem->mem_cgroup_node, &mem_cgroup_soft_limit_exceeded_groups);
> +	__mem_cgroup_remove_exceeded(mem);
>  	spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
>  }
>  
> +static struct mem_cgroup *mem_cgroup_get_largest_soft_limit_exceeding_node(void)
> +{
> +	struct rb_node *rightmost = NULL;
> +	struct mem_cgroup *mem = NULL;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> +	rightmost = rb_last(&mem_cgroup_soft_limit_exceeded_groups);
> +	if (!rightmost)
> +		goto done;		/* Nothing to reclaim from */
> +
> +	mem = rb_entry(rightmost, struct mem_cgroup, mem_cgroup_node);
> +	mem_cgroup_get(mem);
> +	/*
> +	 * Remove the node now but someone else can add it back,
> +	 * we will to add it back at the end of reclaim to its correct
> +	 * position in the tree.
> +	 */
> +	__mem_cgroup_remove_exceeded(mem);
> +done:
> +	spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
> +	return mem;
> +}
> +

Do you remember we discuss about zone reclaim balancing thing 
in "reclaim bail out"thread at about 2 month ago?

The "largest exceeding" policy seems to have similar problems.
if largest exceeding group is most active, 

  1. do the largest group activity and charge memory over softlimit.
  2. reclaim memory from the largest group.
  3. goto 1.

then, system can become livelock.

I think per-group priority is not good idea.



>  static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
>  					 struct page_cgroup *pc,
>  					 bool charge)
> @@ -886,7 +929,8 @@ mem_cgroup_select_victim(struct mem_cgroup *root_mem)
>   * If shrink==true, for avoiding to free too much, this returns immedieately.
>   */
>  static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
> -				   gfp_t gfp_mask, bool noswap, bool shrink)
> +				   gfp_t gfp_mask, bool noswap, bool shrink,
> +				   bool check_soft)

Now, we get three boolean argument.
So, can we convert "int flags" argument?

I don't think mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL, false, true, false) is
self-described good look.


>  {
>  	struct mem_cgroup *victim;
>  	int ret, total = 0;
> @@ -913,7 +957,11 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
>  		if (shrink)
>  			return ret;
>  		total += ret;
> -		if (mem_cgroup_check_under_limit(root_mem))
> +
> +		if (check_soft) {
> +			if (res_counter_soft_limit_excess(&root_mem->res))
> +				return 1 + total;
> +		} else if (mem_cgroup_check_under_limit(root_mem))
>  			return 1 + total;

I don't understand what's mean "1 +".


>  	}
>  	return total;
> @@ -1044,7 +1092,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
>  			goto nomem;
>  
>  		ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
> -							noswap, false);
> +							noswap, false, false);
>  		if (ret)
>  			continue;
>  
> @@ -1686,7 +1734,7 @@ int mem_cgroup_shrink_usage(struct page *page,
>  
>  	do {
>  		progress = mem_cgroup_hierarchical_reclaim(mem,
> -					gfp_mask, true, false);
> +					gfp_mask, true, false, false);
>  		progress += mem_cgroup_check_under_limit(mem);
>  	} while (!progress && --retry);
>  
> @@ -1741,7 +1789,7 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
>  			break;
>  
>  		progress = mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL,
> -						   false, true);
> +						   false, true, false);
>  		curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
>  		/* Usage is reduced ? */
>    		if (curusage >= oldusage)
> @@ -1789,7 +1837,8 @@ int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
>  		if (!ret)
>  			break;
>  
> -		mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL, true, true);
> +		mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL, true, true,
> +						false);
>  		curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
>  		/* Usage is reduced ? */
>  		if (curusage >= oldusage)
> @@ -1940,6 +1989,38 @@ try_to_free:
>  	goto out;
>  }
>  
> +unsigned long mem_cgroup_soft_limit_reclaim(gfp_t gfp_mask)
> +{
> +	unsigned long nr_reclaimed = 0;
> +	struct mem_cgroup *mem;
> +	unsigned long flags;
> +
> +	do {
> +		mem = mem_cgroup_get_largest_soft_limit_exceeding_node();
> +		if (!mem)
> +			break;
> +		if (mem_cgroup_is_obsolete(mem)) {
> +			mem_cgroup_put(mem);
> +			continue;
> +		}
> +		nr_reclaimed +=
> +			mem_cgroup_hierarchical_reclaim(mem, gfp_mask, false,
> +							false, true);
> +		spin_lock_irqsave(&memcg_soft_limit_tree_lock, flags);
> +		mem->usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> +		/*
> +		 * We need to remove and reinsert the node in its correct
> +		 * position
> +		 */
> +		__mem_cgroup_remove_exceeded(mem);
> +		if (mem->usage_in_excess)
> +			__mem_cgroup_insert_exceeded(mem);
> +		spin_unlock_irqrestore(&memcg_soft_limit_tree_lock, flags);
> +		mem_cgroup_put(mem);
> +	} while (!nr_reclaimed);
> +	return nr_reclaimed;
> +}

this function is called from reclaim hotpath. but it grab glocal spin lock..
I don't like this.


> +
>  int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
>  {
>  	return mem_cgroup_force_empty(mem_cgroup_from_cont(cont), true);
> @@ -2528,6 +2609,8 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  	mem->last_scanned_child = 0;
>  	mem->usage_in_excess = 0;
>  	mem->last_tree_update = 0;	/* Yes, time begins at 0 here */
> +	mem->on_tree = false;
> +
>  	spin_lock_init(&mem->reclaim_param_lock);
>  
>  	if (parent)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7be9386..c50e29b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1579,7 +1579,15 @@ nofail_alloc:
>  	reclaim_state.reclaimed_slab = 0;
>  	p->reclaim_state = &reclaim_state;
>  
> -	did_some_progress = try_to_free_pages(zonelist, order, gfp_mask);
> +	did_some_progress = mem_cgroup_soft_limit_reclaim(gfp_mask);
> +	/*
> +	 * If we made no progress or need higher order allocations
> +	 * try_to_free_pages() is still our best bet, since mem_cgroup
> +	 * reclaim does not handle freeing pages greater than order 0
> +	 */
> +	if (!did_some_progress || order)
> +		did_some_progress = try_to_free_pages(zonelist, order,
> +							gfp_mask);
>  
>  	p->reclaim_state = NULL;
>  	p->flags &= ~PF_MEMALLOC;

this is very freqently called place. then we want to
  - if no memcgroup using, no performance regression.
  - if no softlimit but using memcg, performance degression is smaller than 1%.

Do you have any performance number?



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