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Sat, 17 May 2025 07:06:17 -0700 (PDT) Date: Sat, 17 May 2025 10:06:13 -0400 From: Johannes Weiner To: Shakeel Butt Cc: Andrew Morton , Michal Hocko , Roman Gushchin , Muchun Song , Vlastimil Babka , Alexei Starovoitov , Sebastian Andrzej Siewior , Harry Yoo , Yosry Ahmed , Peter Zijlstra , Mathieu Desnoyers , Tejun Heo , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH v3 1/5] memcg: disable kmem charging in nmi for unsupported arch Message-ID: <20250517140613.GB104729@cmpxchg.org> References: <20250516183231.1615590-1-shakeel.butt@linux.dev> <20250516183231.1615590-2-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250516183231.1615590-2-shakeel.butt@linux.dev> On Fri, May 16, 2025 at 11:32:27AM -0700, 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 > --- > Changes since v2: > - reorder the in_nmi() check as suggested by Vlastimil > > include/linux/memcontrol.h | 5 +++++ > mm/memcontrol.c | 15 +++++++++++++++ > 2 files changed, 20 insertions(+) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index f7848f73f41c..53920528821f 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -62,6 +62,11 @@ struct mem_cgroup_reclaim_cookie { > > #ifdef CONFIG_MEMCG > > +#if defined(CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS) || \ > + !defined(CONFIG_HAVE_NMI) || defined(ARCH_HAVE_NMI_SAFE_CMPXCHG) CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG? > +#define MEMCG_SUPPORTS_NMI_CHARGING > +#endif Since it's derived from config symbols, it's better to make this an internal symbol as well. Something like: config MEMCG_NMI_UNSAFE bool depends on HAVE_NMI depends on !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !ARCH_HAVE_NMI_SAFE_CMPXCHG > #define MEM_CGROUP_ID_SHIFT 16 > > struct mem_cgroup_id { > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index e17b698f6243..0f182e4a9da0 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2647,11 +2647,26 @@ static struct obj_cgroup *current_objcg_update(void) > return objcg; > } > > +#ifdef MEMCG_SUPPORTS_NMI_CHARGING > +static inline bool nmi_charging_allowed(void) > +{ > + return true; > +} > +#else > +static inline bool nmi_charging_allowed(void) > +{ > + return false; > +} > +#endif ...drop these... > + > __always_inline struct obj_cgroup *current_obj_cgroup(void) > { > struct mem_cgroup *memcg; > struct obj_cgroup *objcg; > > + if (!nmi_charging_allowed() && in_nmi()) > + return NULL; ..and finally do if (IS_ENABLED(CONFIG_MEMCG_NMI_UNSAFE && in_nmi()) return NULL; here.