Re: [PATCH v2 05/13] mm: Move memcg stack accounting to account_kernel_stack

[Andy Lutomirski <luto@amacapital.net>]

On Fri, Jun 17, 2016 at 1:55 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Fri, Jun 17, 2016 at 01:00:41PM -0700, Andy Lutomirski wrote:
>> We should account for stacks regardless of stack size.  Move it into
>> account_kernel_stack.
>>
>> Fixes: 12580e4b54ba8 ("mm: memcontrol: report kernel stack usage in cgroup2 memory.stat")
>> Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Michal Hocko <mhocko@kernel.org>
>> Cc: linux-mm@kvack.org
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>>  kernel/fork.c | 15 ++++++---------
>>  1 file changed, 6 insertions(+), 9 deletions(-)
>>
>> diff --git a/kernel/fork.c b/kernel/fork.c
>> index be7f006af727..cd2abe6e4e41 100644
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -165,20 +165,12 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>>       struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
>>                                                 THREAD_SIZE_ORDER);
>>
>> -     if (page)
>> -             memcg_kmem_update_page_stat(page, MEMCG_KERNEL_STACK,
>> -                                         1 << THREAD_SIZE_ORDER);
>> -
>>       return page ? page_address(page) : NULL;
>>  }
>>
>>  static inline void free_thread_info(struct thread_info *ti)
>>  {
>> -     struct page *page = virt_to_page(ti);
>> -
>> -     memcg_kmem_update_page_stat(page, MEMCG_KERNEL_STACK,
>> -                                 -(1 << THREAD_SIZE_ORDER));
>> -     __free_kmem_pages(page, THREAD_SIZE_ORDER);
>> +     free_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
>>  }
>>  # else
>>  static struct kmem_cache *thread_info_cache;
>> @@ -227,6 +219,11 @@ static void account_kernel_stack(struct thread_info *ti, int account)
>>
>>       mod_zone_page_state(zone, NR_KERNEL_STACK_KB,
>>                           THREAD_SIZE / 1024 * account);
>> +
>> +     /* All stack pages belong to the same memcg. */
>> +     memcg_kmem_update_page_stat(
>> +             virt_to_page(ti), MEMCG_KERNEL_STACK,
>> +             account * (THREAD_SIZE / PAGE_SIZE));
>>  }
>
> Won't this be broken in the case where THREAD_SIZE < PAGE_SIZE?

In my defense, it was broken before this change, too.  Sigh.  I'll
change this to count in KiB too.

As far as I can tell, this thing is used for display only.

--Andy