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[202.134.99.148]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2aeae22217dsm6012985ad.4.2026.03.10.19.21.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Mar 2026 19:21:55 -0700 (PDT) Message-ID: <18f4092c-35c9-4ac4-a2f5-1039c7d54ec5@shopee.com> Date: Wed, 11 Mar 2026 10:21:49 +0800 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: [PATCH V2 3/4] mm: shrinker: optimize the allocation of shrinker_info when setting cgroup_memory_nokmem To: Usama Arif Cc: akpm@linux-foundation.org, david@fromorbit.com, roman.gushchin@linux.dev, zhengqi.arch@bytedance.com, muchun.song@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260310110536.3474739-1-usama.arif@linux.dev> From: Haifeng Xu In-Reply-To: <20260310110536.3474739-1-usama.arif@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2026/3/10 19:05, Usama Arif wrote: > On Tue, 10 Mar 2026 11:12:49 +0800 Haifeng Xu wrote: > >> When kmem is disabled, memcg slab shrink only call non-slab shrinkers, >> so just allocates shrinker info for non-slab shrinkers to non-root memcgs. >> >> Therefore, if memcg_kmem_online is true, all things keep same as before. >> Otherwise, root memcg allocates id from shrinker_idr to identify each >> shrinker and non-root memcgs use nonslab_id to identify non-slab shrinkers. >> The size of shrinkers_info in non-root memcgs can be very low because the >> number of shrinkers marked as SHRINKER_NONSLAB | SHRINKER_MEMCG_AWARE is >> few. Also, the time spending in expand_shrinker_info() can reduce a lot. >> >> When setting shrinker bit or updating nr_deferred, use nonslab_id for >> non-root memcgs if the shrinker is marked as SHRINKER_NONSLAB. >> >> Signed-off-by: Haifeng Xu >> --- >> include/linux/memcontrol.h | 8 ++- >> include/linux/shrinker.h | 3 + >> mm/shrinker.c | 116 +++++++++++++++++++++++++++++++++---- >> 3 files changed, 114 insertions(+), 13 deletions(-) >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index ce7b5101bc02..3edd6211aed2 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -1804,7 +1804,13 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg); >> >> static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker) >> { >> - return shrinker->id; >> + int id = shrinker->id; >> + >> + if (!memcg_kmem_online() && (shrinker->flags & SHRINKER_NONSLAB) && >> + memcg != root_mem_cgroup) >> + id = shrinker->nonslab_id; >> + >> + return id; >> } >> #else >> #define mem_cgroup_sockets_enabled 0 >> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h >> index 1a00be90d93a..df53008ed8b5 100644 >> --- a/include/linux/shrinker.h >> +++ b/include/linux/shrinker.h >> @@ -107,6 +107,9 @@ struct shrinker { >> #ifdef CONFIG_MEMCG >> /* ID in shrinker_idr */ >> int id; >> + >> + /* ID in shrinker_nonslab_idr */ >> + int nonslab_id; >> #endif >> #ifdef CONFIG_SHRINKER_DEBUG >> int debugfs_id; >> diff --git a/mm/shrinker.c b/mm/shrinker.c >> index 61dbb6afae52..68ea2d49495c 100644 >> --- a/mm/shrinker.c >> +++ b/mm/shrinker.c >> @@ -12,6 +12,7 @@ DEFINE_MUTEX(shrinker_mutex); >> >> #ifdef CONFIG_MEMCG >> static int shrinker_nr_max; >> +static int shrinker_nonslab_nr_max; >> >> static inline int shrinker_unit_size(int nr_items) >> { >> @@ -78,15 +79,25 @@ int alloc_shrinker_info(struct mem_cgroup *memcg) >> { >> int nid, ret = 0; >> int array_size = 0; >> + int alloc_nr_max; >> + >> + if (memcg_kmem_online()) { >> + alloc_nr_max = shrinker_nr_max; >> + } else { >> + if (memcg == root_mem_cgroup) >> + alloc_nr_max = shrinker_nr_max; >> + else >> + alloc_nr_max = shrinker_nonslab_nr_max; >> + } >> >> mutex_lock(&shrinker_mutex); > > Hello! > > The patch reads shrinker_nonslab_nr_max and shrinker_nr_max before > acquiring shrinker_mutex. The original code read shrinker_nr_max > UNDER the lock. Both variables are modified under shrinker_mutex by > concurrent shrinker registrations. A stale read could cause > alloc_shrinker_info() to allocate an undersized shrinker_info, > leading to out-of-bounds access in set_shrinker_bit() or the > nr_deferred functions. > Yes，thanks for pointing out the problems.