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