Re: [PATCH v4 08/11] memcg: add dirty limits to mem_cgroup

[Greg Thelen <gthelen@google.com>]

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> writes:

> On Fri, 29 Oct 2010 00:09:11 -0700
> Greg Thelen <gthelen@google.com> 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.
>> 
>> Signed-off-by: Greg Thelen <gthelen@google.com>
>> Signed-off-by: Andrea Righi <arighi@develer.com>
>> ---
>> Changelog since v3:
>> - Previously memcontrol.c used struct vm_dirty_param and vm_dirty_param() to
>>   advertise dirty memory limits.  Now struct dirty_info and
>>   mem_cgroup_dirty_info() is used to share dirty limits between memcontrol and
>>   the rest of the kernel.
>> - __mem_cgroup_has_dirty_limit() now returns false if use_hierarchy is set.
>
> This seems Okay for our starting point. Hierarchy is always problem..
>
>
>
>> - memcg_hierarchical_free_pages() now uses parent_mem_cgroup() and is simpler.
>> - created internal routine, __mem_cgroup_has_dirty_limit(), to consolidate the
>>   logic.
>> 
>
>
>
>> Changelog since v1:
>> - Rename (for clarity):
>>   - mem_cgroup_write_page_stat_item -> mem_cgroup_page_stat_item
>>   - mem_cgroup_read_page_stat_item -> mem_cgroup_nr_pages_item
>> - Removed unnecessary get_ prefix from get_xxx() functions.
>> - Avoid lockdep warnings by using rcu_read_[un]lock() in
>>   mem_cgroup_has_dirty_limit().
>> 
>>  include/linux/memcontrol.h |   30 ++++++
>>  mm/memcontrol.c            |  248 +++++++++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 277 insertions(+), 1 deletions(-)
>> 
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index ef2eec7..736d318 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 +34,14 @@ enum mem_cgroup_page_stat_item {
>>  	MEMCG_NR_FILE_UNSTABLE_NFS, /* # of NFS unstable pages */
>>  };
>>  
>> +/* Cgroup memory statistics items exported to the kernel. */
>> +enum mem_cgroup_nr_pages_item {
>> +	MEMCG_NR_DIRTYABLE_PAGES,
>> +	MEMCG_NR_RECLAIM_PAGES,
>> +	MEMCG_NR_WRITEBACK,
>> +	MEMCG_NR_DIRTY_WRITEBACK_PAGES,
>> +};
>> +
>>  extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>>  					struct list_head *dst,
>>  					unsigned long *scanned, int order,
>> @@ -145,6 +154,11 @@ 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);
>> +bool mem_cgroup_dirty_info(unsigned long sys_available_mem,
>> +			   struct dirty_info *info);
>> +s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_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 +340,22 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
>>  {
>>  }
>>  
>> +static inline bool mem_cgroup_has_dirty_limit(void)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline bool mem_cgroup_dirty_info(unsigned long sys_available_mem,
>> +					 struct dirty_info *info)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_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 7f91029..52d688d 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -188,6 +188,14 @@ struct mem_cgroup_eventfd_list {
>>  static void mem_cgroup_threshold(struct mem_cgroup *mem);
>>  static void mem_cgroup_oom_notify(struct mem_cgroup *mem);
>>  
>> +/* Dirty memory parameters */
>> +struct vm_dirty_param {
>> +	int dirty_ratio;
>> +	int dirty_background_ratio;
>> +	unsigned long dirty_bytes;
>> +	unsigned long dirty_background_bytes;
>> +};
>> +
>>  /*
>>   * The memory controller data structure. The memory controller controls both
>>   * page cache and RSS per cgroup. We would eventually like to provide
>> @@ -233,6 +241,10 @@ 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 +1144,232 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg)
>>  	return swappiness;
>>  }
>>  
>> +/*
>> + * Return true if the current memory cgroup has local dirty memory settings.
>> + * There is an allowed race between the current task migrating in-to/out-of the
>> + * root cgroup while this routine runs.  So the return value may be incorrect if
>> + * the current task is being simultaneously migrated.
>> + */
>> +static bool __mem_cgroup_has_dirty_limit(struct mem_cgroup *mem)
>> +{
>> +	if (!mem)
>> +		return false;
>> +	if (mem_cgroup_is_root(mem))
>> +		return false;
>> +	/*
>> +	 * The current memcg implementation does not yet support hierarchical
>> +	 * dirty limits.
>> +	 */
>> +	if (mem->use_hierarchy)
>> +		return false;
>> +	return true;
>> +}
>> +
>> +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_cgroup_has_dirty_limit(mem);
>> +	rcu_read_unlock();
>> +
>> +	return ret;
>> +}
>> +
>> +/*
>> + * 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_dirty_param(struct vm_dirty_param *param,
>> +				     struct mem_cgroup *mem)
>> +{
>> +	if (__mem_cgroup_has_dirty_limit(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 {
>> +		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;
>> +	}
>> +}
>> +
>> +/*
>> + * Return the background-writeback and dirty-throttling thresholds as well as
>> + * dirty usage metrics.
>> + *
>> + * The current task may be moved to another cgroup while this routine accesses
>> + * the dirty limit.  But a 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 while holding rcu_read_lock().
>> + */
>> +bool mem_cgroup_dirty_info(unsigned long sys_available_mem,
>> +			   struct dirty_info *info)
>> +{
>> +	s64 available_mem;
>> +	struct vm_dirty_param dirty_param;
>> +	struct mem_cgroup *memcg;
>> +
>> +	if (mem_cgroup_disabled())
>> +		return false;
>> +
>> +	rcu_read_lock();
>> +	memcg = mem_cgroup_from_task(current);
>> +	if (!__mem_cgroup_has_dirty_limit(memcg)) {
>> +		rcu_read_unlock();
>> +		return false;
>> +	}
>> +	__mem_cgroup_dirty_param(&dirty_param, memcg);
>> +	rcu_read_unlock();
>
> Hmm, don't we need to get css_get() for this "memcg" ?

The memcg variable is not directly used later in this routine.  memcg is
only used in this routine while holding rcu_read_lock().
mem_cgroup_page_stat calls (below) query memcg from the current task.
So I do not think that css_get() is needed.

>> +
>> +	available_mem = mem_cgroup_page_stat(MEMCG_NR_DIRTYABLE_PAGES);
>> +	if (available_mem < 0)
>> +		return false;
>> +
>> +	available_mem = min((unsigned long)available_mem, sys_available_mem);
>> +
> This seems nice.
>
>> +	if (dirty_param.dirty_bytes)
>> +		info->dirty_thresh =
>> +			DIV_ROUND_UP(dirty_param.dirty_bytes, PAGE_SIZE);
>> +	else
>> +		info->dirty_thresh =
>> +			(dirty_param.dirty_ratio * available_mem) / 100;
>> +
>> +	if (dirty_param.dirty_background_bytes)
>> +		info->background_thresh =
>> +			DIV_ROUND_UP(dirty_param.dirty_background_bytes,
>> +				     PAGE_SIZE);
>> +	else
>> +		info->background_thresh =
>> +			(dirty_param.dirty_background_ratio *
>> +			       available_mem) / 100;
>> +
>
> Okay, then these will be finally double-checked with system's dirty-info.
> Right ?

balance_dirty_pages() calls both global_dirty_info() and
memcg_dirty_info() to determine dirty limits and usage for both the
system and the current memcg.  Both the system and memcg limits are
checked by balance_dirty_pages().

> Thanks,
> -Kame
>
>> +	info->nr_reclaimable =
>> +		mem_cgroup_page_stat(MEMCG_NR_RECLAIM_PAGES);
>> +	if (info->nr_reclaimable < 0)
>> +		return false;
>> +
>> +	info->nr_writeback = mem_cgroup_page_stat(MEMCG_NR_WRITEBACK);
>> +	if (info->nr_writeback < 0)
>> +		return false;
>> +
>> +	return true;
>> +}
>> +
>> +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_local_page_stat(struct mem_cgroup *mem,
>> +				      enum mem_cgroup_nr_pages_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;
>> +}
>> +
>> +/*
>> + * Return the number of pages that the @mem cgroup could allocate.  If
>> + * use_hierarchy is set, then this involves parent mem cgroups to find the
>> + * cgroup with the smallest free space.
>> + */
>> +static unsigned long long
>> +memcg_hierarchical_free_pages(struct mem_cgroup *mem)
>> +{
>> +	unsigned long free, min_free;
>> +
>> +	min_free = global_page_state(NR_FREE_PAGES) << PAGE_SHIFT;
>> +
>> +	while (mem) {
>> +		free = res_counter_read_u64(&mem->res, RES_LIMIT) -
>> +			res_counter_read_u64(&mem->res, RES_USAGE);
>> +		min_free = min(min_free, free);
>> +		mem = parent_mem_cgroup(mem);
>> +	}
>> +
>> +	/* 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 or negative value if current task is
>> + * root cgroup.
>> + */
>> +s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item)
>> +{
>> +	struct mem_cgroup *mem;
>> +	struct mem_cgroup *iter;
>> +	s64 value;
>> +
>> +	rcu_read_lock();
>> +	mem = mem_cgroup_from_task(current);
>> +	if (__mem_cgroup_has_dirty_limit(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_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_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;
>> @@ -4440,8 +4678,16 @@ 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_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);
>> -- 
>> 1.7.3.1
>> 
>> 

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