On Wed 03-03-21 17:39:56, Muchun Song wrote:
> 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.
>
> 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.
You have skipped over one part of the changelog I have proposed and that
is to provide an actual data.
> Address the problem by accounting each vmalloc backing page to its own
> node.
>
> Fixes: 991e7673859e ("mm: memcontrol: account kernel stack per node")
Fixes tag might make somebody assume this is worth backporting but I
highly doubt so.
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Anyway
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
as the patch is correct with one comment below
> ---
> Changelog in v2:
> - Rework commit log suggested by Michal.
>
> Thanks to Michal and Shakeel for review.
>
> kernel/fork.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d66cd1014211..6e2201feb524 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -379,14 +379,19 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
> 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
> + BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
I do not think we need this BUG_ON. What kind of purpose does it serve?
> +
> + 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)
> --
> 2.11.0
--
Michal Hocko
SUSE Labs
