Re: [PATCH V3 5/8] memcg: add per cgroup writeback pages accounting

[Sha Zhengju <handai.szj@gmail.com>]

On Mon, Jan 7, 2013 at 4:07 AM, Greg Thelen <gthelen@google.com> wrote:
> On Tue, Dec 25 2012, Sha Zhengju wrote:
>
>> From: Sha Zhengju <handai.szj@taobao.com>
>>
>> Similar to dirty page, we add per cgroup writeback pages accounting. The lock
>> rule still is:
>>         mem_cgroup_begin_update_page_stat()
>>         modify page WRITEBACK stat
>>         mem_cgroup_update_page_stat()
>>         mem_cgroup_end_update_page_stat()
>>
>> There're two writeback interface to modify: test_clear/set_page_writeback.
>>
>> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
>> ---
>>  include/linux/memcontrol.h |    1 +
>>  mm/memcontrol.c            |    5 +++++
>>  mm/page-writeback.c        |   17 +++++++++++++++++
>>  3 files changed, 23 insertions(+)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 358019e..1d22b81 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -45,6 +45,7 @@ enum mem_cgroup_stat_index {
>>       MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
>>       MEM_CGROUP_STAT_SWAP, /* # of pages, swapped out */
>>       MEM_CGROUP_STAT_FILE_DIRTY,  /* # of dirty pages in page cache */
>> +     MEM_CGROUP_STAT_WRITEBACK,  /* # of pages under writeback */
>>       MEM_CGROUP_STAT_NSTATS,
>>  };
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 21df36d..13cd14a 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -96,6 +96,7 @@ static const char * const mem_cgroup_stat_names[] = {
>>       "mapped_file",
>>       "swap",
>>       "dirty",
>> +     "writeback",
>>  };
>>
>>  enum mem_cgroup_events_index {
>> @@ -3676,6 +3677,10 @@ static int mem_cgroup_move_account(struct page *page,
>>               mem_cgroup_move_account_page_stat(from, to, nr_pages,
>>                       MEM_CGROUP_STAT_FILE_DIRTY);
>>
>> +     if (PageWriteback(page))
>> +             mem_cgroup_move_account_page_stat(from, to, nr_pages,
>> +                     MEM_CGROUP_STAT_WRITEBACK);
>> +
>>       mem_cgroup_charge_statistics(from, anon, -nr_pages);
>>
>>       /* caller should have done css_get */
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index 526ddd7..ae6498a 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -2002,11 +2002,17 @@ EXPORT_SYMBOL(account_page_dirtied);
>>
>>  /*
>>   * Helper function for set_page_writeback family.
>> + *
>> + * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
>> + * while modifying struct page state and accounting writeback pages.
>> + * See test_set_page_writeback for example.
>> + *
>>   * NOTE: Unlike account_page_dirtied this does not rely on being atomic
>>   * wrt interrupts.
>>   */
>>  void account_page_writeback(struct page *page)
>>  {
>> +     mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
>>       inc_zone_page_state(page, NR_WRITEBACK);
>>  }
>>  EXPORT_SYMBOL(account_page_writeback);
>> @@ -2242,7 +2248,10 @@ int test_clear_page_writeback(struct page *page)
>>  {
>>       struct address_space *mapping = page_mapping(page);
>>       int ret;
>> +     bool locked;
>> +     unsigned long memcg_flags;
>>
>> +     mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
>
> Does this violate lock ordering?  Here we are grabbing
> mem_cgroup_begin_update_page_stat and below we grab tree_lock.  I
> thought the prescribed order was tree_lock first, then
> mem_cgroup_begin_update_page_stat.

Yes, tree_lock should go first. Sorry it's my fault to forget to check
this one.
Thanks for reminding!

>>       if (mapping) {
>>               struct backing_dev_info *bdi = mapping->backing_dev_info;
>>               unsigned long flags;
>> @@ -2263,9 +2272,12 @@ int test_clear_page_writeback(struct page *page)
>>               ret = TestClearPageWriteback(page);
>>       }
>>       if (ret) {
>> +             mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
>>               dec_zone_page_state(page, NR_WRITEBACK);
>>               inc_zone_page_state(page, NR_WRITTEN);
>>       }
>> +
>> +     mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
>>       return ret;
>>  }
>>
>> @@ -2273,7 +2285,10 @@ int test_set_page_writeback(struct page *page)
>>  {
>>       struct address_space *mapping = page_mapping(page);
>>       int ret;
>> +     bool locked;
>> +     unsigned long flags;
>>
>> +     mem_cgroup_begin_update_page_stat(page, &locked, &flags);
>
> Same "Does this violate lock ordering?" question as above.

OK, got it.
>>       if (mapping) {
>>               struct backing_dev_info *bdi = mapping->backing_dev_info;
>>               unsigned long flags;
>> @@ -2300,6 +2315,8 @@ int test_set_page_writeback(struct page *page)
>>       }
>>       if (!ret)
>>               account_page_writeback(page);
>> +
>> +     mem_cgroup_end_update_page_stat(page, &locked, &flags);
>>       return ret;
>>
>>  }



-- 
Thanks,
Sha

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