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

[Andrea Righi]

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

> +
> +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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