Re: [RFC] [PATCH 5/7 v2] memcg: remove PCG_FILE_MAPPED

[Ying Han <yinghan@google.com>]

On Thu, Jan 19, 2012 at 6:07 AM, Michal Hocko <mhocko@suse.cz> wrote:
> On Fri 13-01-12 17:42:23, KAMEZAWA Hiroyuki wrote:
>> From a9b51d6204d7f8714173c46a306caf413ad25d4e Mon Sep 17 00:00:00 2001
>> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> Date: Thu, 12 Jan 2012 18:40:26 +0900
>> Subject: [PATCH 5/7] memcg: remove PCG_FILE_MAPPED
>>
>> Because we can update page's status and memcg's statistics without
>> race with move_account, this flag is unnecessary.
>
> I would really appreciate a little bit more description ;)
>
> 8725d541 [memcg: fix race in file_mapped accounting] has added the
> flag to resolve a race when a move_account happened between page's
> mapcount has been updated and this has been accounted to memcg.
> This, however, cannot happen anymore because mem_cgroup_update_page_stat
> is always enclosed by mem_cgroup_begin_update_page_stat and
> mem_cgroup_end_update_page_stat along with the mapcount update.

Agree on better documentation.

>
>>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> Other than that looks good and nice to see another one go away.
> I will add my ack along with the patches which this depend on once they
> settle down if you don't mind
>
> Thanks
>
>> ---
>>  include/linux/page_cgroup.h |    6 ------
>>  mm/memcontrol.c             |    6 +-----
>>  2 files changed, 1 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
>> index 5dba799..0b9a48a 100644
>> --- a/include/linux/page_cgroup.h
>> +++ b/include/linux/page_cgroup.h
>> @@ -7,8 +7,6 @@ enum {
>>       PCG_CACHE, /* charged as cache */
>>       PCG_USED, /* this object is in use. */
>>       PCG_MIGRATION, /* under page migration */
>> -     /* flags for mem_cgroup and file and I/O status */
>> -     PCG_FILE_MAPPED, /* page is accounted as "mapped" */
>>       __NR_PCG_FLAGS,
>>  };
>>
>> @@ -72,10 +70,6 @@ TESTPCGFLAG(Used, USED)
>>  CLEARPCGFLAG(Used, USED)
>>  SETPCGFLAG(Used, USED)
>>
>> -SETPCGFLAG(FileMapped, FILE_MAPPED)
>> -CLEARPCGFLAG(FileMapped, FILE_MAPPED)
>> -TESTPCGFLAG(FileMapped, FILE_MAPPED)
>> -
>>  SETPCGFLAG(Migration, MIGRATION)
>>  CLEARPCGFLAG(Migration, MIGRATION)
>>  TESTPCGFLAG(Migration, MIGRATION)
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 30ef810..a96800d 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1952,10 +1952,6 @@ void mem_cgroup_update_page_stat(struct page *page,
>>
>>       switch (idx) {
>>       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:
>> @@ -2606,7 +2602,7 @@ static int mem_cgroup_move_account(struct page *page,
>>
>>       mem_cgroup_account_move_wlock(page, &flags);
>>
>> -     if (PageCgroupFileMapped(pc)) {
>> +     if (page_mapcount(page)) {

Does it includes anon pages , should it be

if (page_mapped(page) && !PageAnon(page))

--Ying

>>               /* Update mapped_file data for mem_cgroup */
>>               preempt_disable();
>>               __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
>> --
>> 1.7.4.1
>>
>>
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>
> --
> Michal Hocko
> SUSE Labs
> SUSE LINUX s.r.o.
> Lihovarska 1060/12
> 190 00 Praha 9
> Czech Republic

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