Re: [PATCH 07/10] memcg: add dirty limits to mem_cgroup

[Greg Thelen]

Andrea Righi <arighi@xxxxxxxxxxx> writes:

> On Sun, Oct 03, 2010 at 11:58:02PM -0700, Greg Thelen wrote:
>> Extend mem_cgroup to contain dirty page limits.  Also add routines
>> allowing the kernel to query the dirty usage of a memcg.
>> 
>> These interfaces not used by the kernel yet.  A subsequent commit
>> will add kernel calls to utilize these new routines.
>
> A small note below.
>
>> 
>> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
>> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx>
>> ---
>>  include/linux/memcontrol.h |   44 +++++++++++
>>  mm/memcontrol.c            |  180 +++++++++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 223 insertions(+), 1 deletions(-)
>> 
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 6303da1..dc8952d 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -19,6 +19,7 @@
>>  
>>  #ifndef _LINUX_MEMCONTROL_H
>>  #define _LINUX_MEMCONTROL_H
>> +#include <linux/writeback.h>
>>  #include <linux/cgroup.h>
>>  struct mem_cgroup;
>>  struct page_cgroup;
>> @@ -33,6 +34,30 @@ enum mem_cgroup_write_page_stat_item {
>>  	MEMCG_NR_FILE_UNSTABLE_NFS, /* # of NFS unstable pages */
>>  };
>>  
>> +/* Cgroup memory statistics items exported to the kernel */
>> +enum mem_cgroup_read_page_stat_item {
>> +	MEMCG_NR_DIRTYABLE_PAGES,
>> +	MEMCG_NR_RECLAIM_PAGES,
>> +	MEMCG_NR_WRITEBACK,
>> +	MEMCG_NR_DIRTY_WRITEBACK_PAGES,
>> +};
>> +
>> +/* Dirty memory parameters */
>> +struct vm_dirty_param {
>> +	int dirty_ratio;
>> +	int dirty_background_ratio;
>> +	unsigned long dirty_bytes;
>> +	unsigned long dirty_background_bytes;
>> +};
>> +
>> +static inline void get_global_vm_dirty_param(struct vm_dirty_param *param)
>> +{
>> +	param->dirty_ratio = vm_dirty_ratio;
>> +	param->dirty_bytes = vm_dirty_bytes;
>> +	param->dirty_background_ratio = dirty_background_ratio;
>> +	param->dirty_background_bytes = dirty_background_bytes;
>> +}
>> +
>>  extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>>  					struct list_head *dst,
>>  					unsigned long *scanned, int order,
>> @@ -145,6 +170,10 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>>  	mem_cgroup_update_page_stat(page, idx, -1);
>>  }
>>  
>> +bool mem_cgroup_has_dirty_limit(void);
>> +void get_vm_dirty_param(struct vm_dirty_param *param);
>> +s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item);
>> +
>>  unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>>  						gfp_t gfp_mask);
>>  u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
>> @@ -326,6 +355,21 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>>  {
>>  }
>>  
>> +static inline bool mem_cgroup_has_dirty_limit(void)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline void get_vm_dirty_param(struct vm_dirty_param *param)
>> +{
>> +	get_global_vm_dirty_param(param);
>> +}
>> +
>> +static inline s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item)
>> +{
>> +	return -ENOSYS;
>> +}
>> +
>>  static inline
>>  unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>>  					    gfp_t gfp_mask)
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index f40839f..6ec2625 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -233,6 +233,10 @@ struct mem_cgroup {
>>  	atomic_t	refcnt;
>>  
>>  	unsigned int	swappiness;
>> +
>> +	/* control memory cgroup dirty pages */
>> +	struct vm_dirty_param dirty_param;
>> +
>>  	/* OOM-Killer disable */
>>  	int		oom_kill_disable;
>>  
>> @@ -1132,6 +1136,172 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg)
>>  	return swappiness;
>>  }
>>  
>> +/*
>> + * Returns a snapshot of the current dirty limits which is not synchronized with
>> + * the routines that change the dirty limits.  If this routine races with an
>> + * update to the dirty bytes/ratio value, then the caller must handle the case
>> + * where both dirty_[background_]_ratio and _bytes are set.
>> + */
>> +static void __mem_cgroup_get_dirty_param(struct vm_dirty_param *param,
>> +					 struct mem_cgroup *mem)
>> +{
>> +	if (mem && !mem_cgroup_is_root(mem)) {
>> +		param->dirty_ratio = mem->dirty_param.dirty_ratio;
>> +		param->dirty_bytes = mem->dirty_param.dirty_bytes;
>> +		param->dirty_background_ratio =
>> +			mem->dirty_param.dirty_background_ratio;
>> +		param->dirty_background_bytes =
>> +			mem->dirty_param.dirty_background_bytes;
>> +	} else {
>> +		get_global_vm_dirty_param(param);
>> +	}
>> +}
>> +
>> +/*
>> + * Get dirty memory parameters of the current memcg or global values (if memory
>> + * cgroups are disabled or querying the root cgroup).
>> + */
>> +void get_vm_dirty_param(struct vm_dirty_param *param)
>> +{
>> +	struct mem_cgroup *memcg;
>> +
>> +	if (mem_cgroup_disabled()) {
>> +		get_global_vm_dirty_param(param);
>> +		return;
>> +	}
>> +
>> +	/*
>> +	 * It's possible that "current" may be moved to other cgroup while we
>> +	 * access cgroup. But precise check is meaningless because the task can
>> +	 * be moved after our access and writeback tends to take long time.  At
>> +	 * least, "memcg" will not be freed under rcu_read_lock().
>> +	 */
>> +	rcu_read_lock();
>> +	memcg = mem_cgroup_from_task(current);
>> +	__mem_cgroup_get_dirty_param(param, memcg);
>> +	rcu_read_unlock();
>> +}
>> +
>> +/*
>> + * Check if current memcg has local dirty limits.  Return true if the current
>> + * memory cgroup has local dirty memory settings.
>> + */
>> +bool mem_cgroup_has_dirty_limit(void)
>> +{
>> +	struct mem_cgroup *mem;
>> +
>> +	if (mem_cgroup_disabled())
>> +		return false;
>> +
>> +	mem = mem_cgroup_from_task(current);
>> +	return mem && !mem_cgroup_is_root(mem);
>> +}
>
> We only check the pointer without dereferencing it, so this is probably
> ok, but maybe this is safer:
>
> bool mem_cgroup_has_dirty_limit(void)
> {
> 	struct mem_cgroup *mem;
> 	bool ret;
>
> 	if (mem_cgroup_disabled())
> 		return false;
>
> 	rcu_read_lock();
> 	mem = mem_cgroup_from_task(current);
> 	ret = mem && !mem_cgroup_is_root(mem);
> 	rcu_read_unlock();
>
> 	return ret;
> }
>
> rcu_read_lock() should be held in mem_cgroup_from_task(), otherwise
> lockdep could detect this as an error.
>
> Thanks,
> -Andrea

Good suggestion.  I agree that lockdep might catch this.  There are some
unrelated debug_locks failures (even without my patches) that I worked
around to get lockdep to complain about this one.  I applied your
suggested fix and lockdep was happy.  I will incorporate this fix into
the next revision of the patch series.

>> +
>> +static inline bool mem_cgroup_can_swap(struct mem_cgroup *memcg)
>> +{
>> +	if (!do_swap_account)
>> +		return nr_swap_pages > 0;
>> +	return !memcg->memsw_is_minimum &&
>> +		(res_counter_read_u64(&memcg->memsw, RES_LIMIT) > 0);
>> +}
>> +
>> +static s64 mem_cgroup_get_local_page_stat(struct mem_cgroup *mem,
>> +				enum mem_cgroup_read_page_stat_item item)
>> +{
>> +	s64 ret;
>> +
>> +	switch (item) {
>> +	case MEMCG_NR_DIRTYABLE_PAGES:
>> +		ret = mem_cgroup_read_stat(mem, LRU_ACTIVE_FILE) +
>> +			mem_cgroup_read_stat(mem, LRU_INACTIVE_FILE);
>> +		if (mem_cgroup_can_swap(mem))
>> +			ret += mem_cgroup_read_stat(mem, LRU_ACTIVE_ANON) +
>> +				mem_cgroup_read_stat(mem, LRU_INACTIVE_ANON);
>> +		break;
>> +	case MEMCG_NR_RECLAIM_PAGES:
>> +		ret = mem_cgroup_read_stat(mem,	MEM_CGROUP_STAT_FILE_DIRTY) +
>> +			mem_cgroup_read_stat(mem,
>> +					     MEM_CGROUP_STAT_FILE_UNSTABLE_NFS);
>> +		break;
>> +	case MEMCG_NR_WRITEBACK:
>> +		ret = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_FILE_WRITEBACK);
>> +		break;
>> +	case MEMCG_NR_DIRTY_WRITEBACK_PAGES:
>> +		ret = mem_cgroup_read_stat(mem,
>> +					   MEM_CGROUP_STAT_FILE_WRITEBACK) +
>> +			mem_cgroup_read_stat(mem,
>> +					     MEM_CGROUP_STAT_FILE_UNSTABLE_NFS);
>> +		break;
>> +	default:
>> +		BUG();
>> +		break;
>> +	}
>> +	return ret;
>> +}
>> +
>> +static unsigned long long
>> +memcg_get_hierarchical_free_pages(struct mem_cgroup *mem)
>> +{
>> +	struct cgroup *cgroup;
>> +	unsigned long long min_free, free;
>> +
>> +	min_free = res_counter_read_u64(&mem->res, RES_LIMIT) -
>> +		res_counter_read_u64(&mem->res, RES_USAGE);
>> +	cgroup = mem->css.cgroup;
>> +	if (!mem->use_hierarchy)
>> +		goto out;
>> +
>> +	while (cgroup->parent) {
>> +		cgroup = cgroup->parent;
>> +		mem = mem_cgroup_from_cont(cgroup);
>> +		if (!mem->use_hierarchy)
>> +			break;
>> +		free = res_counter_read_u64(&mem->res, RES_LIMIT) -
>> +			res_counter_read_u64(&mem->res, RES_USAGE);
>> +		min_free = min(min_free, free);
>> +	}
>> +out:
>> +	/* Translate free memory in pages */
>> +	return min_free >> PAGE_SHIFT;
>> +}
>> +
>> +/*
>> + * mem_cgroup_page_stat() - get memory cgroup file cache statistics
>> + * @item:      memory statistic item exported to the kernel
>> + *
>> + * Return the accounted statistic value.
>> + */
>> +s64 mem_cgroup_page_stat(enum mem_cgroup_read_page_stat_item item)
>> +{
>> +	struct mem_cgroup *mem;
>> +	struct mem_cgroup *iter;
>> +	s64 value;
>> +
>> +	rcu_read_lock();
>> +	mem = mem_cgroup_from_task(current);
>> +	if (mem && !mem_cgroup_is_root(mem)) {
>> +		/*
>> +		 * If we're looking for dirtyable pages we need to evaluate
>> +		 * free pages depending on the limit and usage of the parents
>> +		 * first of all.
>> +		 */
>> +		if (item == MEMCG_NR_DIRTYABLE_PAGES)
>> +			value = memcg_get_hierarchical_free_pages(mem);
>> +		else
>> +			value = 0;
>> +		/*
>> +		 * Recursively evaluate page statistics against all cgroup
>> +		 * under hierarchy tree
>> +		 */
>> +		for_each_mem_cgroup_tree(iter, mem)
>> +			value += mem_cgroup_get_local_page_stat(iter, item);
>> +	} else
>> +		value = -EINVAL;
>> +	rcu_read_unlock();
>> +
>> +	return value;
>> +}
>> +
>>  static void mem_cgroup_start_move(struct mem_cgroup *mem)
>>  {
>>  	int cpu;
>> @@ -4444,8 +4614,16 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>>  	spin_lock_init(&mem->reclaim_param_lock);
>>  	INIT_LIST_HEAD(&mem->oom_notify);
>>  
>> -	if (parent)
>> +	if (parent) {
>>  		mem->swappiness = get_swappiness(parent);
>> +		__mem_cgroup_get_dirty_param(&mem->dirty_param, parent);
>> +	} else {
>> +		/*
>> +		 * The root cgroup dirty_param field is not used, instead,
>> +		 * system-wide dirty limits are used.
>> +		 */
>> +	}
>> +
>>  	atomic_set(&mem->refcnt, 1);
>>  	mem->move_charge_at_immigrate = 0;
>>  	mutex_init(&mem->thresholds_lock);
>> -- 
>> 1.7.1
>> 
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