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McKenney" , Huang Shijie , Guo Weikang , "Uladzislau Rezki (Sony)" , KP Singh , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hyeonggon Yoo , Paul Moore , opensource.kernel@vivo.com Subject: Re: [PATCH v3 3/3] mm/memcg: use kmem_cache when alloc memcg pernode info Message-ID: <20250427120036.GC116315@cmpxchg.org> References: <20250425031935.76411-1-link@vivo.com> <20250425031935.76411-4-link@vivo.com> 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: <20250425031935.76411-4-link@vivo.com> On Fri, Apr 25, 2025 at 11:19:25AM +0800, Huan Yang wrote: > When tracing mem_cgroup_per_node allocations with kmalloc ftrace: > > kmalloc: call_site=mem_cgroup_css_alloc+0x1d8/0x5b4 ptr=00000000d798700c > bytes_req=2896 bytes_alloc=4096 gfp_flags=GFP_KERNEL|__GFP_ZERO node=0 > accounted=false > > This reveals the slab allocator provides 4096B chunks for 2896B > mem_cgroup_per_node due to: > > 1. The slab allocator predefines bucket sizes from 64B to 8096B > 2. The mem_cgroup allocation size (2312B) falls between the 2KB and 4KB > slabs > 3. The allocator rounds up to the nearest larger slab (4KB), resulting in > ~1KB wasted memory per memcg alloc - per node. > > This patch introduces a dedicated kmem_cache for mem_cgroup structs, > achieving precise memory allocation. Post-patch ftrace verification shows: > > kmem_cache_alloc: call_site=mem_cgroup_css_alloc+0x1b8/0x5d4 > ptr=000000002989e63a bytes_req=2896 bytes_alloc=2944 > gfp_flags=GFP_KERNEL|__GFP_ZERO node=0 accounted=false > > Each mem_cgroup_per_node alloc 2944bytes(include hw cacheline align), > compare to 4096, it avoid waste. > > Signed-off-by: Huan Yang Acked-by: Johannes Weiner