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

[Josh Poimboeuf]

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@xxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
>  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?

-- 
Josh