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

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  [PATCH 2/4] mm: Fix memcg stack accounting for sub-page stacks Andy Lutomirski <luto@kernel.org> - 2016-07-14 21:20 +0200
    Re: [PATCH 2/4] mm: Fix memcg stack accounting for sub-page stacks Johannes Weiner <hannes@cmpxchg.org> - 2016-07-14 21:30 +0200
    Re: [PATCH 2/4] mm: Fix memcg stack accounting for sub-page stacks Andrew Morton <akpm@linux-foundation.org> - 2016-07-14 23:00 +0200

#1443705 — [PATCH 2/4] mm: Fix memcg stack accounting for sub-page stacks

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().

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
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 include/linux/memcontrol.h |  2 +-
 kernel/fork.c              | 19 ++++++++-----------
 mm/memcontrol.c            |  2 +-
 3 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a805474df4ab..3b653b86bb8f 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -52,7 +52,7 @@ enum mem_cgroup_stat_index {
 	MEM_CGROUP_STAT_SWAP,		/* # of pages, swapped out */
 	MEM_CGROUP_STAT_NSTATS,
 	/* default hierarchy stats */
-	MEMCG_KERNEL_STACK = MEM_CGROUP_STAT_NSTATS,
+	MEMCG_KERNEL_STACK_KB = MEM_CGROUP_STAT_NSTATS,
 	MEMCG_SLAB_RECLAIMABLE,
 	MEMCG_SLAB_UNRECLAIMABLE,
 	MEMCG_SOCK,
diff --git a/kernel/fork.c b/kernel/fork.c
index 466ba8febe3b..146c9840c079 100644
--- 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);
 }
 # else
 static struct kmem_cache *thread_stack_cache;
@@ -223,10 +215,15 @@ static struct kmem_cache *mm_cachep;
 
 static void account_kernel_stack(unsigned long *stack, int account)
 {
-	struct zone *zone = page_zone(virt_to_page(stack));
+	/* All stack pages are in the same zone and belong to the same memcg. */
+	struct page *first_page = virt_to_page(stack);
 
-	mod_zone_page_state(zone, NR_KERNEL_STACK_KB,
+	mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
 			    THREAD_SIZE / 1024 * account);
+
+	memcg_kmem_update_page_stat(
+		first_page, MEMCG_KERNEL_STACK_KB,
+		account * (THREAD_SIZE / 1024));
 }
 
 void free_task(struct task_struct *tsk)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ac8664db3823..ee44afc1f2d0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5133,7 +5133,7 @@ static int memory_stat_show(struct seq_file *m, void *v)
 	seq_printf(m, "file %llu\n",
 		   (u64)stat[MEM_CGROUP_STAT_CACHE] * PAGE_SIZE);
 	seq_printf(m, "kernel_stack %llu\n",
-		   (u64)stat[MEMCG_KERNEL_STACK] * PAGE_SIZE);
+		   (u64)stat[MEMCG_KERNEL_STACK_KB] * 1024);
 	seq_printf(m, "slab %llu\n",
 		   (u64)(stat[MEMCG_SLAB_RECLAIMABLE] +
 			 stat[MEMCG_SLAB_UNRECLAIMABLE]) * PAGE_SIZE);
-- 
2.7.4

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#1443715

On Thu, Jul 14, 2016 at 12:14:11PM -0700, Andy Lutomirski 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().
> 
> 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
> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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#1443776

On Thu, 14 Jul 2016 12:14:11 -0700 Andy Lutomirski <luto@kernel.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);
}

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