[PATCH v4 07/16] mm: Fix memcg stack accounting for sub-page stacks

[Andy Lutomirski <luto@kernel.org>]

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: 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              | 15 ++++++---------
 mm/memcontrol.c            |  2 +-
 3 files changed, 8 insertions(+), 11 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 be7f006af727..ff3c41c2ba96 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_KB,
+		account * (THREAD_SIZE / 1024));
 }
 
 void free_task(struct task_struct *tsk)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 75e74408cc8f..8e13a2419dad 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);
-- 
2.5.5