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Wed, 29 Oct 2025 11:45:51 -0700 (PDT) Message-ID: Date: Wed, 29 Oct 2025 19:45:32 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH V3 6/7] mm/slab: save memory by allocating slabobj_ext array from leftover To: Harry Yoo , akpm@linux-foundation.org, vbabka@suse.cz Cc: andreyknvl@gmail.com, cl@linux.com, dvyukov@google.com, glider@google.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev, rientjes@google.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, surenb@google.com, vincenzo.frascino@arm.com, yeoreum.yun@arm.com, tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org References: <20251027122847.320924-1-harry.yoo@oracle.com> <20251027122847.320924-7-harry.yoo@oracle.com> Content-Language: en-US From: Andrey Ryabinin In-Reply-To: <20251027122847.320924-7-harry.yoo@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/27/25 1:28 PM, Harry Yoo wrote: > > +#ifdef CONFIG_SLAB_OBJ_EXT > + > +/* > + * Check if memory cgroup or memory allocation profiling is enabled. > + * If enabled, SLUB tries to reduce memory overhead of accounting > + * slab objects. If neither is enabled when this function is called, > + * the optimization is simply skipped to avoid affecting caches that do not > + * need slabobj_ext metadata. > + * > + * However, this may disable optimization when memory cgroup or memory > + * allocation profiling is used, but slabs are created too early > + * even before those subsystems are initialized. > + */ > +static inline bool need_slab_obj_exts(struct kmem_cache *s) > +{ > + if (!mem_cgroup_disabled() && (s->flags & SLAB_ACCOUNT)) Shouldn't this be !memcg_kmem_online() check? In case of disabled kmem accounting via 'cgroup.memory=nokmem' > + return true; > + > + if (mem_alloc_profiling_enabled()) > + return true; > + > + return false; > +} > +