linux-kernel - Re: [PATCH 2/4] mm: Fix memcg stack accounting for sub-page stacks

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Message-Id: <20160714135310.ba2b7dcca48184538260ec21@linux-foundation.org>
Date:	Thu, 14 Jul 2016 13:53:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Brian Gerst <brgerst@...il.com>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/4] mm: Fix memcg stack accounting for sub-page stacks

On Thu, 14 Jul 2016 12:14:11 -0700 Andy Lutomirski <luto@...nel.org> wrote:

> We should account for stacks regardless of stack size, and we need
> to account in sub-page units if THREAD_SIZE < PAGE_SIZE.  Change the
> units to kilobytes and Move it into account_kernel_stack().

I queued this patch after
http://ozlabs.org/~akpm/mmotm/broken-out/mm-charge-uncharge-kmemcg-from-generic-page-allocator-paths.patch
so some changes are needed.  (patching mainline when we're at -rc7 was
optimistic!)

> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -165,20 +165,12 @@ static unsigned long *alloc_thread_stack_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_stack(unsigned long *stack)
>  {
> -	struct page *page = virt_to_page(stack);
> -
> -	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)stack, THREAD_SIZE_ORDER);
>  }

Here's what I ended up with:

static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
						  int node)
{
	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
					     THREAD_SIZE_ORDER);

	return page ? page_address(page) : NULL;
}

static inline void free_thread_stack(unsigned long *stack)
{
	__free_pages(virt_to_page(stack), THREAD_SIZE_ORDER);
}