diff mbox series

[056/178] mm: memcontrol: fix kernel stack account

Message ID 20210430055602._TPiM7mzp%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/178] arch/ia64/kernel/head.S: remove duplicate include | expand

Commit Message

Andrew Morton April 30, 2021, 5:56 a.m. UTC
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm: memcontrol: fix kernel stack account

For simplification 991e7673859e ("mm: memcontrol: account kernel stack per
node") has changed the per zone vmalloc backed stack pages accounting to
per node.  By doing that we have lost a certain precision because those
pages might live in different NUMA nodes.  In the end NR_KERNEL_STACK_KB
exported to the userspace might be over estimated on some nodes while
underestimated on others.  But this is not a real world problem, just a
problem found by reading the code.  So there is no actual data to showing
how much impact it has on users.

This doesn't impose any real problem to correctnes of the kernel behavior
as the counter is not used for any internal processing but it can cause
some confusion to the userspace.

Address the problem by accounting each vmalloc backing page to its own

Link: https://lkml.kernel.org/r/20210303151843.81156-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

 kernel/fork.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)
diff mbox series


--- a/kernel/fork.c~mm-memcontrol-fix-kernel-stack-account
+++ a/kernel/fork.c
@@ -380,14 +380,17 @@  static void account_kernel_stack(struct
 	void *stack = task_stack_page(tsk);
 	struct vm_struct *vm = task_stack_vm_area(tsk);
+	if (vm) {
+		int i;
-	/* All stack pages are in the same node. */
-	if (vm)
-		mod_lruvec_page_state(vm->pages[0], NR_KERNEL_STACK_KB,
-				      account * (THREAD_SIZE / 1024));
-	else
+		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
+			mod_lruvec_page_state(vm->pages[i], NR_KERNEL_STACK_KB,
+					      account * (PAGE_SIZE / 1024));
+	} else {
+		/* All stack pages are in the same node. */
 		mod_lruvec_kmem_state(stack, NR_KERNEL_STACK_KB,
 				      account * (THREAD_SIZE / 1024));
+	}
 static int memcg_charge_kernel_stack(struct task_struct *tsk)