linux-kernel - Re: [PATCH v4 1/5] memcg: disable kmem charging in nmi for unsupported arch

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Message-ID: <9a8de744-cccd-4d05-8243-ff2b1ff65393@suse.cz>
Date: Mon, 19 May 2025 08:46:22 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Shakeel Butt <shakeel.butt@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>, Alexei Starovoitov <ast@...nel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Harry Yoo <harry.yoo@...cle.com>, Yosry Ahmed <yosry.ahmed@...ux.dev>,
 Peter Zijlstra <peterz@...radead.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Tejun Heo
 <tj@...nel.org>, bpf@...r.kernel.org, linux-mm@...ck.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH v4 1/5] memcg: disable kmem charging in nmi for
 unsupported arch

On 5/19/25 08:31, Shakeel Butt wrote:
> The memcg accounting and stats uses this_cpu* and atomic* ops. There are
> archs which define CONFIG_HAVE_NMI but does not define
> CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS and ARCH_HAVE_NMI_SAFE_CMPXCHG, so
> memcg accounting for such archs in nmi context is not possible to
> support. Let's just disable memcg accounting in nmi context for such
> archs.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  init/Kconfig    | 7 +++++++
>  mm/memcontrol.c | 3 +++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 4cdd1049283c..a2aa49cfb8bd 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1006,6 +1006,13 @@ config MEMCG
>  	help
>  	  Provides control over the memory footprint of tasks in a cgroup.
>  
> +config MEMCG_NMI_UNSAFE
> +	bool
> +	depends on MEMCG
> +	depends on HAVE_NMI
> +	depends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !ARCH_HAVE_NMI_SAFE_CMPXCHG
> +	default y
> +
>  config MEMCG_V1
>  	bool "Legacy cgroup v1 memory controller"
>  	depends on MEMCG
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e17b698f6243..532e2c06ea60 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2652,6 +2652,9 @@ __always_inline struct obj_cgroup *current_obj_cgroup(void)
>  	struct mem_cgroup *memcg;
>  	struct obj_cgroup *objcg;
>  
> +	if (IS_ENABLED(CONFIG_MEMCG_NMI_UNSAFE) && in_nmi())
> +		return NULL;
> +
>  	if (in_task()) {
>  		memcg = current->active_memcg;
>  		if (unlikely(memcg))