Re: [RFC][PATCH 2/2] memcg: hardwall hierarhcy for memcg

[Balbir Singh <balbir@linux.vnet.ibm.com>]

KAMEZAWA Hiroyuki wrote:
> Hard-Wall hierarchy support for memcg.
>  - new member hierarchy_model is added to memcg.
> 
> Only root cgroup can modify this only when there is no children.
> 

Sounds like the correct thing TODO and also maintains compatibility

> Adds following functions for supporting HARDWALL hierarchy.
>  - try to reclaim memory at the change of "limit".
>  - try to reclaim all memory at force_empty
>  - returns resources to the parent at destroy.
> 
> Changelog v2->v3
>  - added documentation.
>  - hierarhcy_model parameter is added.
> 
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> ---
>  Documentation/controllers/memory.txt |   27 +++++-
>  mm/memcontrol.c                      |  156 ++++++++++++++++++++++++++++++++++-
>  2 files changed, 178 insertions(+), 5 deletions(-)
> 
> Index: temp-2.6.26-rc2-mm1/mm/memcontrol.c
> ===================================================================
> --- temp-2.6.26-rc2-mm1.orig/mm/memcontrol.c
> +++ temp-2.6.26-rc2-mm1/mm/memcontrol.c
> @@ -137,6 +137,8 @@ struct mem_cgroup {
>  	struct mem_cgroup_lru_info info;
> 
>  	int	prev_priority;	/* for recording reclaim priority */
> +
> +	int	hierarchy_model; /* used hierarchical policy */

Could we enumerate what these policies are?

>  	/*
>  	 * statistics.
>  	 */
> @@ -144,6 +146,10 @@ struct mem_cgroup {
>  };
>  static struct mem_cgroup init_mem_cgroup;
> 
> +
> +#define MEMCG_NO_HIERARCHY	(0)

Nice to indent with the #define below

> +#define MEMCG_HARDWALL_HIERARCHY	(1)
> +
>  /*
>   * We use the lower bit of the page->page_cgroup pointer as a bit spin
>   * lock.  We need to ensure that page->page_cgroup is at least two
> @@ -792,6 +798,89 @@ int mem_cgroup_shrink_usage(struct mm_st
>  }
> 
>  /*
> + * Memory Controller hierarchy support.
> + */
> +
> +/*
> + * shrink usage to be res->usage + val < res->limit.
> + */
> +
> +int memcg_shrink_val(struct res_counter *cnt, unsigned long long val)
> +{
> +	struct mem_cgroup *memcg = container_of(cnt, struct mem_cgroup, res);
> +	unsigned long flags;
> +	int ret = 1;
> +	int progress = 1;
> +
> +retry:
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	/* Need to shrink ? */
> +	if (cnt->usage + val <= cnt->limit)
> +		ret = 0;
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +

We have res_counter_check_under_limit(), may be we could re-use that here by
adding parameters.

> +	if (!ret)
> +		return 0;
> +
> +	if (!progress)
> +		return 1;
> +	progress = try_to_free_mem_cgroup_pages(memcg, GFP_KERNEL);
> +
> +	goto retry;
> +}
> +
> +/*
> + * For Hard Wall Hierarchy.
> + */
> +
> +int mem_cgroup_resize_callback(struct res_counter *cnt,
> +			unsigned long long val, int what)
> +{
> +	unsigned long flags, borrow;
> +	unsigned long long diffs;
> +	int ret = 0;
> +
> +	BUG_ON(what != RES_LIMIT);
> +
> +	/* Is this under hierarchy ? */
> +	if (!cnt->parent) {
> +		spin_lock_irqsave(&cnt->lock, flags);
> +		cnt->limit = val;

I know callback is called from the two functions specified in patch 1/2 (move
and return resource). I don't understand why it is OK to force the limit to be
val, if it is the root node?

> +		spin_unlock_irqrestore(&cnt->lock, flags);
> +		return 0;
> +	}
> +
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	if (val > cnt->limit) {
> +		diffs = val - cnt->limit;
> +		borrow = 1;
> +	} else {
> +		diffs = cnt->limit - val;
> +		borrow = 0;
> +	}
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +
> +	if (borrow)
> +		ret = res_counter_move_resource(cnt,diffs,
> +					memcg_shrink_val,
> +					MEM_CGROUP_RECLAIM_RETRIES);
> +	else
> +		ret = res_counter_return_resource(cnt, diffs,
> +					memcg_shrink_val,
> +					MEM_CGROUP_RECLAIM_RETRIES);
> +	return ret;
> +}
> +
> +
> +void memcg_shrink_all(struct mem_cgroup *mem)
> +{

memcg_shrink_to_limit?

> +	unsigned long long val;
> +
> +	val = res_counter_read_u64(&mem->res, RES_LIMIT);
> +	memcg_shrink_val(&mem->res, val);
> +}
> +
> +/*
>   * This routine traverse page_cgroup in given list and drop them all.
>   * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
>   */
> @@ -848,6 +937,8 @@ static int mem_cgroup_force_empty(struct
>  	if (mem_cgroup_subsys.disabled)
>  		return 0;
> 
> +	memcg_shrink_all(mem);
> +
>  	css_get(&mem->css);
>  	/*
>  	 * page reclaim code (kswapd etc..) will move pages between
> @@ -896,11 +987,44 @@ static ssize_t mem_cgroup_write(struct c
>  				struct file *file, const char __user *userbuf,
>  				size_t nbytes, loff_t *ppos)
>  {
> -	return res_counter_write(&mem_cgroup_from_cont(cont)->res,
> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
> +
> +	if (cft->private != RES_LIMIT
> +		|| !cont->parent
> +		|| memcg->hierarchy_model == MEMCG_NO_HIERARCHY)
> +		return res_counter_write(&memcg->res, cft->private, userbuf,
> +			nbytes, ppos, mem_cgroup_write_strategy, NULL);
> +	else
> +		return res_counter_write(&memcg->res,
>  				cft->private, userbuf, nbytes, ppos,
> -				mem_cgroup_write_strategy);
> +				mem_cgroup_write_strategy,
> +				mem_cgroup_resize_callback);
> +}
> +
> +
> +static u64 mem_cgroup_read_hierarchy(struct cgroup *cgrp, struct cftype *cft)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +	return memcg->hierarchy_model;
> +}
> +
> +static int mem_cgroup_write_hierarchy(struct cgroup *cgrp, struct cftype *cft,
> +				u64 val)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +	/* chage policy is allowed to ROOT cgroup && no children */
> +	if (cgrp->parent)
> +		return -EINVAL;
> +	if (!list_empty(&cgrp->children))
> +		return -EINVAL;
> +	if (val == 0 || val == 1) {
> +		memcg->hierarchy_model = val;
> +		return 0;
> +	}
> +	return -EINVAL;
>  }
> 
> +
>  static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
>  {
>  	struct mem_cgroup *mem;
> @@ -992,6 +1116,16 @@ static struct cftype mem_cgroup_files[] 
>  		.name = "stat",
>  		.read_map = mem_control_stat_show,
>  	},
> +	{
> +		.name = "hierarchy_model",
> +		.read_u64 = mem_cgroup_read_hierarchy,
> +		.write_u64 = mem_cgroup_write_hierarchy,
> +	},
> +	{
> +		.name = "assigned_to_child",
> +		.private = RES_FOR_CHILDREN,
> +		.read_u64 = mem_cgroup_read,
> +	},
>  };
> 
>  static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
> @@ -1056,19 +1190,27 @@ static void mem_cgroup_free(struct mem_c
>  static struct cgroup_subsys_state *
>  mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  {
> -	struct mem_cgroup *mem;
> +	struct mem_cgroup *mem, *parent;
>  	int node;
> 
>  	if (unlikely((cont->parent) == NULL)) {
>  		mem = &init_mem_cgroup;
>  		page_cgroup_cache = KMEM_CACHE(page_cgroup, SLAB_PANIC);
> +		parent = NULL;
>  	} else {
>  		mem = mem_cgroup_alloc();
>  		if (!mem)
>  			return ERR_PTR(-ENOMEM);
> +		parent = mem_cgroup_from_cont(cont->parent);
>  	}
> 
> -	res_counter_init(&mem->res);
> +	if (!parent || parent->hierarchy_model == MEMCG_NO_HIERARCHY) {
> +		res_counter_init(&mem->res);
> +		mem->hierarchy_model = MEMCG_NO_HIERARCHY;
> +	} else {
> +		res_counter_init_hierarchy(&mem->res, &parent->res);
> +		mem->hierarchy_model = parent->hierarchy_model;
> +	}
> 
>  	for_each_node_state(node, N_POSSIBLE)
>  		if (alloc_mem_cgroup_per_zone_info(mem, node))
> @@ -1096,6 +1238,12 @@ static void mem_cgroup_destroy(struct cg
>  	int node;
>  	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> 
> +	if (cont->parent &&
> +	    mem->hierarchy_model == MEMCG_HARDWALL_HIERARCHY) {
> +		/* we did what we can...just returns what we borrow */
> +		res_counter_return_resource(&mem->res, -1, NULL, 0);
> +	}
> +
>  	for_each_node_state(node, N_POSSIBLE)
>  		free_mem_cgroup_per_zone_info(mem, node);
> 
> Index: temp-2.6.26-rc2-mm1/Documentation/controllers/memory.txt
> ===================================================================
> --- temp-2.6.26-rc2-mm1.orig/Documentation/controllers/memory.txt
> +++ temp-2.6.26-rc2-mm1/Documentation/controllers/memory.txt
> @@ -237,12 +237,37 @@ cgroup might have some charge associated
>  tasks have migrated away from it. Such charges are automatically dropped at
>  rmdir() if there are no tasks.
> 
> -5. TODO
> +5. Hierarchy Model
> +  the kernel supports following kinds of hierarchy models.
> +  (your middle-ware may support others based on this.)
> +
> +  5-a. Independent Hierarchy
> +  There are no relationship between any cgroups, even among a parent and
> +  children. This is the default mode. To use this hierarchy, write 0
> +  to root cgroup's memory.hierarchy_model
> +  echo 0 > .../memory.hierarchy_model.
> +
> +  5-b. Hardwall Hierarchy.
> +  The resource has to be moved from the parent to the child before use it.
> +  When a child's limit is set to 'val', val of the resource is moved from
> +  the parent to the child. the parent's usage += val.
> +  The amount of children's usage is reported by the file
> +
> +  - memory.assigned_to_child
> +
> +  This policy doesn't provide sophisticated automatic resource balancing in
> +  the kernel. But this is very good for strict resource isolation. Users
> +  can get high predictability of behavior of applications if this is used
> +  under proper environments.
> +
> +
> +6. TODO
> 
>  1. Add support for accounting huge pages (as a separate controller)
>  2. Make per-cgroup scanner reclaim not-shared pages first
>  3. Teach controller to account for shared-pages
>  4. Start reclamation when the limit is lowered
> +   (this is already done in Hardwall Hierarchy)

Excellent! May be we should split this patch out?

>  5. Start reclamation in the background when the limit is
>     not yet hit but the usage is getting closer
> 
> 


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

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