Re: [PATCH 03/10] memcg: create extensible page stat update routines

[Greg Thelen]

KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes:

> On Sun,  3 Oct 2010 23:57:58 -0700
> Greg Thelen <gthelen@xxxxxxxxxx> wrote:
>
>> Replace usage of the mem_cgroup_update_file_mapped() memcg
>> statistic update routine with two new routines:
>> * mem_cgroup_inc_page_stat()
>> * mem_cgroup_dec_page_stat()
>> 
>> As before, only the file_mapped statistic is managed.  However,
>> these more general interfaces allow for new statistics to be
>> more easily added.  New statistics are added with memcg dirty
>> page accounting.
>> 
>> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
>> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx>
>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> a nitpick. see below.
>
>> ---
>>  include/linux/memcontrol.h |   31 ++++++++++++++++++++++++++++---
>>  mm/memcontrol.c            |   17 ++++++++---------
>>  mm/rmap.c                  |    4 ++--
>>  3 files changed, 38 insertions(+), 14 deletions(-)
>> 
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 159a076..7c7bec4 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -25,6 +25,11 @@ struct page_cgroup;
>>  struct page;
>>  struct mm_struct;
>>  
>> +/* Stats that can be updated by kernel. */
>> +enum mem_cgroup_write_page_stat_item {
>> +	MEMCG_NR_FILE_MAPPED, /* # of pages charged as file rss */
>> +};
>> +
>>  extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>>  					struct list_head *dst,
>>  					unsigned long *scanned, int order,
>> @@ -121,7 +126,22 @@ static inline bool mem_cgroup_disabled(void)
>>  	return false;
>>  }
>>  
>> -void mem_cgroup_update_file_mapped(struct page *page, int val);
>> +void mem_cgroup_update_page_stat(struct page *page,
>> +				 enum mem_cgroup_write_page_stat_item idx,
>> +				 int val);
>> +
>> +static inline void mem_cgroup_inc_page_stat(struct page *page,
>> +				enum mem_cgroup_write_page_stat_item idx)
>> +{
>> +	mem_cgroup_update_page_stat(page, idx, 1);
>> +}
>> +
>> +static inline void mem_cgroup_dec_page_stat(struct page *page,
>> +				enum mem_cgroup_write_page_stat_item idx)
>> +{
>> +	mem_cgroup_update_page_stat(page, idx, -1);
>> +}
>> +
>>  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);
>> @@ -293,8 +313,13 @@ mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
>>  {
>>  }
>>  
>> -static inline void mem_cgroup_update_file_mapped(struct page *page,
>> -							int val)
>> +static inline void mem_cgroup_inc_page_stat(struct page *page,
>> +				enum mem_cgroup_write_page_stat_item idx)
>> +{
>> +}
>> +
>> +static inline void mem_cgroup_dec_page_stat(struct page *page,
>> +				enum mem_cgroup_write_page_stat_item idx)
>>  {
>>  }
>>  
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 512cb12..f4259f4 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1592,7 +1592,9 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
>>   * possibility of race condition. If there is, we take a lock.
>>   */
>>  
>> -static void mem_cgroup_update_file_stat(struct page *page, int idx, int val)
>> +void mem_cgroup_update_page_stat(struct page *page,
>> +				 enum mem_cgroup_write_page_stat_item idx,
>> +				 int val)
>>  {
>>  	struct mem_cgroup *mem;
>>  	struct page_cgroup *pc = lookup_page_cgroup(page);
>> @@ -1615,30 +1617,27 @@ static void mem_cgroup_update_file_stat(struct page *page, int idx, int val)
>>  			goto out;
>>  	}
>>  
>> -	this_cpu_add(mem->stat->count[idx], val);
>> -
>>  	switch (idx) {
>> -	case MEM_CGROUP_STAT_FILE_MAPPED:
>> +	case MEMCG_NR_FILE_MAPPED:
>>  		if (val > 0)
>>  			SetPageCgroupFileMapped(pc);
>>  		else if (!page_mapped(page))
>>  			ClearPageCgroupFileMapped(pc);
>> +		idx = MEM_CGROUP_STAT_FILE_MAPPED;
>>  		break;
>>  	default:
>>  		BUG();
>>  	}
>>  
>> +	this_cpu_add(mem->stat->count[idx], val);
>> +
>
> Why you move this_cpu_add() placement ?
> (This placement is ok but I just wonder..)
>
> Thanks,
> -Kame

The reason this_cpu_add() is moved to after the switch is because the
switch is needed to convert the input parameter from an enum
mem_cgroup_write_page_stat_item (example: MEMCG_NR_FILE_MAPPED) to enum
mem_cgroup_stat_index (example: MEM_CGROUP_STAT_FILE_MAPPED) before
indexing into the count array.

Also in subsequent patches (in this series) "val" is updated depending
on page_cgroup flags before usage by this_cpu_add().
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