linux-kernel - Re: [PATCH v2] mm: memcontrol: fix kernel stack account

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Date:   Wed, 3 Mar 2021 10:14:58 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     guro@...com, mhocko@...nel.org, akpm@...ux-foundation.org,
        shakeelb@...gle.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: memcontrol: fix kernel stack account

On Wed, Mar 03, 2021 at 05:39:56PM +0800, 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.
> 
> Address the problem by accounting each vmalloc backing page to its own
> node.
> 
> Fixes: 991e7673859e ("mm: memcontrol: account kernel stack per node")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>

With changes proposed by Shakeel and Michal, this looks good to me.

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

I guess the BUG_ON() was inspired by memcg_charge_kernel_stack() - not
really your fault for following that example. But yeah, please drop it
from your patch. Thanks!