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[70.44.39.90]) by smtp.gmail.com with ESMTPSA id h23sm2064825qtr.21.2021.04.15.09.30.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Apr 2021 09:30:53 -0700 (PDT) Date: Thu, 15 Apr 2021 12:30:53 -0400 From: Johannes Weiner To: Waiman Long Cc: Michal Hocko , Vladimir Davydov , Andrew Morton , Tejun Heo , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Muchun Song , Alex Shi , Chris Down , Yafang Shao , Wei Yang , Masayoshi Mizuma , Xing Zhengjun Subject: Re: [PATCH v3 2/5] mm/memcg: Introduce obj_cgroup_uncharge_mod_state() Message-ID: References: <20210414012027.5352-1-longman@redhat.com> <20210414012027.5352-3-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210414012027.5352-3-longman@redhat.com> X-Stat-Signature: rb8kcitcecbsihurwaaho5cwo44cx975 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B15ECC0007D2 Received-SPF: none (cmpxchg.org>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=mail-qk1-f174.google.com; client-ip=209.85.222.174 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618504246-475348 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 13, 2021 at 09:20:24PM -0400, Waiman Long wrote: > In memcg_slab_free_hook()/pcpu_memcg_free_hook(), obj_cgroup_uncharge() > is followed by mod_objcg_state()/mod_memcg_state(). Each of these > function call goes through a separate irq_save/irq_restore cycle. That > is inefficient. Introduce a new function obj_cgroup_uncharge_mod_state() > that combines them with a single irq_save/irq_restore cycle. > > @@ -3292,6 +3296,25 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size) > refill_obj_stock(objcg, size); > } > > +void obj_cgroup_uncharge_mod_state(struct obj_cgroup *objcg, size_t size, > + struct pglist_data *pgdat, int idx) The optimization makes sense. But please don't combine independent operations like this into a single function. It makes for an unclear parameter list, it's a pain in the behind to change the constituent operations later on, and it has a habit of attracting more random bools over time. E.g. what if the caller already has irqs disabled? What if it KNOWS that irqs are enabled and it could use local_irq_disable() instead of save? Just provide an __obj_cgroup_uncharge() that assumes irqs are disabled, combine with the existing __mod_memcg_lruvec_state(), and bubble the irq handling up to those callsites which know better.