Re: [RFC][-mm] Memory controller hierarchy support (v1)

[Pavel Emelyanov]

Balbir Singh wrote:
> This applies on top of 2.6.25-rc8-mm2. The next version will be applied
> on top of 2.5.25-mm1.
> 
> This code is built on top of Pavel's hierarchy patches.
> 
> 1. It propagates the charges upwards. A charge incurred on a cgroup
>    is propagated to root. If any of the counters along the hierarchy
>    is over limit, reclaim is initiated from the parent. We reclaim
>    pages from the parent and the children below it. We also keep track
>    of the last child from whom reclaim was done and start from there in
>    the next reclaim.

Are you going to split this patch? As is it looks rather huge :)

> TODO's/Open Questions
> 
> 1. We need to hold cgroup_mutex while walking through the children
>    in reclaim. We need to figure out the best way to do so. Should
>    cgroups provide a helper function/macro for it?
> 2. Do not allow children to have a limit greater than their parents.
> 3. Allow the user to select if hierarchial support is required
> 4. Fine tune reclaim from children logic
> 
> Testing
> 
> This code was tested on a UML instance, where it compiled and worked well.
> 
> Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxx>
> Signed-off-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> ---
> 
>  include/linux/res_counter.h |   14 ++++
>  kernel/res_counter.c        |   42 +++++++++++---
>  mm/memcontrol.c             |  128 +++++++++++++++++++++++++++++++++++---------
>  3 files changed, 148 insertions(+), 36 deletions(-)
> 
> diff -puN include/linux/res_counter.h~memory-controller-hierarchy-support include/linux/res_counter.h
> --- linux-2.6.25-rc8/include/linux/res_counter.h~memory-controller-hierarchy-support	2008-04-19 11:00:28.000000000 +0530
> +++ linux-2.6.25-rc8-balbir/include/linux/res_counter.h	2008-04-19 11:00:28.000000000 +0530
> @@ -43,6 +43,10 @@ struct res_counter {
>  	 * the routines below consider this to be IRQ-safe
>  	 */
>  	spinlock_t lock;
> +	/*
> +	 * the parent counter. used for hierarchical resource accounting
> +	 */
> +	struct res_counter *parent;
>  };
>  
>  /**
> @@ -82,7 +86,12 @@ enum {
>   * helpers for accounting
>   */
>  
> -void res_counter_init(struct res_counter *counter);
> +/*
> + * the parent pointer is set only once - during the counter
> + * initialization. caller then must itself provide that this
> + * pointer is valid during the new counter lifetime
> + */
> +void res_counter_init(struct res_counter *counter, struct res_counter *parent);
>  
>  /*
>   * charge - try to consume more resource.
> @@ -96,7 +105,8 @@ void res_counter_init(struct res_counter
>   */
>  
>  int res_counter_charge_locked(struct res_counter *counter, unsigned long val);
> -int res_counter_charge(struct res_counter *counter, unsigned long val);
> +int res_counter_charge(struct res_counter *counter, unsigned long val,
> +				struct res_counter **limit_exceeded_at);
>  
>  /*
>   * uncharge - tell that some portion of the resource is released
> diff -puN kernel/res_counter.c~memory-controller-hierarchy-support kernel/res_counter.c
> --- linux-2.6.25-rc8/kernel/res_counter.c~memory-controller-hierarchy-support	2008-04-19 11:00:28.000000000 +0530
> +++ linux-2.6.25-rc8-balbir/kernel/res_counter.c	2008-04-19 11:00:28.000000000 +0530
> @@ -14,10 +14,11 @@
>  #include <linux/res_counter.h>
>  #include <linux/uaccess.h>
>  
> -void res_counter_init(struct res_counter *counter)
> +void res_counter_init(struct res_counter *counter, struct res_counter *parent)
>  {
>  	spin_lock_init(&counter->lock);
>  	counter->limit = (unsigned long long)LLONG_MAX;
> +	counter->parent = parent;
>  }
>  
>  int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
> @@ -33,14 +34,34 @@ int res_counter_charge_locked(struct res
>  	return 0;
>  }
>  
> -int res_counter_charge(struct res_counter *counter, unsigned long val)
> +int res_counter_charge(struct res_counter *counter, unsigned long val,
> +			struct res_counter **limit_exceeded_at)
>  {
>  	int ret;
>  	unsigned long flags;
> +	struct res_counter *c, *unroll_c;
>  
> -	spin_lock_irqsave(&counter->lock, flags);
> -	ret = res_counter_charge_locked(counter, val);
> -	spin_unlock_irqrestore(&counter->lock, flags);
> +	*limit_exceeded_at = NULL;
> +	local_irq_save(flags);
> +	for (c = counter; c != NULL; c = c->parent) {
> +		spin_lock(&c->lock);
> +		ret = res_counter_charge_locked(c, val);
> +		spin_unlock(&c->lock);
> +		if (ret < 0) {
> +			*limit_exceeded_at = c;
> +			goto unroll;
> +		}
> +	}
> +	local_irq_restore(flags);
> +	return 0;
> +
> +unroll:
> +	for (unroll_c = counter; unroll_c != c; unroll_c = unroll_c->parent) {
> +		spin_lock(&unroll_c->lock);
> +		res_counter_uncharge_locked(unroll_c, val);
> +		spin_unlock(&unroll_c->lock);
> +	}
> +	local_irq_restore(flags);
>  	return ret;
>  }
>  
> @@ -55,10 +76,15 @@ void res_counter_uncharge_locked(struct 
>  void res_counter_uncharge(struct res_counter *counter, unsigned long val)
>  {
>  	unsigned long flags;
> +	struct res_counter *c;
>  
> -	spin_lock_irqsave(&counter->lock, flags);
> -	res_counter_uncharge_locked(counter, val);
> -	spin_unlock_irqrestore(&counter->lock, flags);
> +	local_irq_save(flags);
> +	for (c = counter; c != NULL; c = c->parent) {
> +		spin_lock(&c->lock);
> +		res_counter_uncharge_locked(c, val);
> +		spin_unlock(&c->lock);
> +	}
> +	local_irq_restore(flags);
>  }
>  
>  
> diff -puN mm/memcontrol.c~memory-controller-hierarchy-support mm/memcontrol.c
> --- linux-2.6.25-rc8/mm/memcontrol.c~memory-controller-hierarchy-support	2008-04-19 11:00:28.000000000 +0530
> +++ linux-2.6.25-rc8-balbir/mm/memcontrol.c	2008-04-19 11:00:28.000000000 +0530
> @@ -138,6 +138,13 @@ struct mem_cgroup {
>  	 * statistics.
>  	 */
>  	struct mem_cgroup_stat stat;
> +
> +	/*
> +	 * When reclaiming in a hierarchy, we need to know, which child
> +	 * we reclaimed last from. This helps us avoid hitting the first
> +	 * child over and over again
> +	 */
> +	struct mem_cgroup *last_scanned_child;
>  };
>  static struct mem_cgroup init_mem_cgroup;
>  
> @@ -244,6 +251,12 @@ struct mem_cgroup *mem_cgroup_from_task(
>  				struct mem_cgroup, css);
>  }
>  
> +static struct mem_cgroup*
> +mem_cgroup_from_res_counter(struct res_counter *counter)
> +{
> +	return container_of(counter, struct mem_cgroup, res);
> +}
> +
>  static inline int page_cgroup_locked(struct page *page)
>  {
>  	return bit_spin_is_locked(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
> @@ -508,6 +521,86 @@ unsigned long mem_cgroup_isolate_pages(u
>  }
>  
>  /*
> + * Charge mem and check if it is over it's limit. If so, reclaim from
> + * mem. This function can call itself recursively (as we walk up the
> + * hierarchy).
> + */
> +static int mem_cgroup_charge_and_reclaim(struct mem_cgroup *mem, gfp_t gfp_mask)
> +{
> +	int ret = 0;
> +	unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> +	struct res_counter *counter_over_limit;
> +	struct mem_cgroup *mem_over_limit;
> +	struct cgroup *cgroup, *cgrp, *curr_cgroup;
> +
> +	while (res_counter_charge(&mem->res, PAGE_SIZE, &counter_over_limit)) {
> +		if (!(gfp_mask & __GFP_WAIT))
> +			goto out;
> +
> +		/*
> +		 * Is one of our ancestors over limit ?
> +		 */
> +		if (counter_over_limit) {
> +			mem_over_limit =
> +				mem_cgroup_from_res_counter(counter_over_limit);
> +
> +			if (mem != mem_over_limit)
> +				ret = mem_cgroup_charge_and_reclaim(
> +						mem_over_limit, gfp_mask);
> +		}
> +
> +		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> +			continue;
> +
> +		/*
> +		 * try_to_free_mem_cgroup_pages() might not give us a full
> +		 * picture of reclaim. Some pages are reclaimed and might be
> +		 * moved to swap cache or just unmapped from the cgroup.
> +		 * Check the limit again to see if the reclaim reduced the
> +		 * current usage of the cgroup before giving up
> +		 */
> +		if (res_counter_check_under_limit(&mem->res))
> +			continue;
> +
> +		/*
> +		 * Now scan all children under the group. This is required
> +		 * to support hierarchies
> +		 */
> +		if (!mem->last_scanned_child)
> +			cgroup = list_first_entry(&mem->css.cgroup->children,
> +						struct cgroup, sibling);
> +		else
> +			cgroup = mem->last_scanned_child->css.cgroup;
> +
> +		curr_cgroup = mem->css.cgroup;
> +
> +		/*
> +		 * Ideally we need to hold cgroup_mutex here
> +		 */
> +		list_for_each_entry_safe_from(cgroup, cgrp,
> +				&curr_cgroup->children, sibling) {
> +			struct mem_cgroup *mem_child;
> +
> +			mem_child = mem_cgroup_from_cont(cgroup);
> +			ret = try_to_free_mem_cgroup_pages(mem_child,
> +								gfp_mask);
> +			mem->last_scanned_child = mem_child;
> +			if (ret == 0)
> +				break;
> +		}
> +
> +		if (!nr_retries--) {
> +			mem_cgroup_out_of_memory(mem, gfp_mask);
> +			ret = -ENOMEM;
> +			break;
> +		}
> +	}
> +
> +out:
> +	return ret;
> +}
> +
> +/*
>   * Charge the memory controller for page usage.
>   * Return
>   * 0 if the charge was successful
> @@ -519,7 +612,6 @@ static int mem_cgroup_charge_common(stru
>  	struct mem_cgroup *mem;
>  	struct page_cgroup *pc;
>  	unsigned long flags;
> -	unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
>  	struct mem_cgroup_per_zone *mz;
>  
>  	if (mem_cgroup_subsys.disabled)
> @@ -570,28 +662,8 @@ retry:
>  	css_get(&mem->css);
>  	rcu_read_unlock();
>  
> -	while (res_counter_charge(&mem->res, PAGE_SIZE)) {
> -		if (!(gfp_mask & __GFP_WAIT))
> -			goto out;
> -
> -		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> -			continue;
> -
> -		/*
> -		 * try_to_free_mem_cgroup_pages() might not give us a full
> -		 * picture of reclaim. Some pages are reclaimed and might be
> -		 * moved to swap cache or just unmapped from the cgroup.
> -		 * Check the limit again to see if the reclaim reduced the
> -		 * current usage of the cgroup before giving up
> -		 */
> -		if (res_counter_check_under_limit(&mem->res))
> -			continue;
> -
> -		if (!nr_retries--) {
> -			mem_cgroup_out_of_memory(mem, gfp_mask);
> -			goto out;
> -		}
> -	}
> +	if (mem_cgroup_charge_and_reclaim(mem, gfp_mask))
> +		goto out;
>  
>  	pc->ref_cnt = 1;
>  	pc->mem_cgroup = mem;
> @@ -986,19 +1058,23 @@ static void free_mem_cgroup_per_zone_inf
>  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);
> -	} else
> +		parent = NULL;
> +	} else {
>  		mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
> +		parent = mem_cgroup_from_cont(cont->parent);
> +	}
>  
>  	if (mem == NULL)
>  		return ERR_PTR(-ENOMEM);
>  
> -	res_counter_init(&mem->res);
> +	res_counter_init(&mem->res, parent ? &parent->res : NULL);
> +	mem->last_scanned_child = NULL;

I though about it recently. Can we have a cgroup file, which will
control whether to attach a res_counter to the parent? This will
address the YEMEMOTO's question about the performance.

>  	memset(&mem->info, 0, sizeof(mem->info));
>  
> _
> 

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