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AJvYcCVbRfHmGPHUWTJUXBGFlDSws8sqB9yHF2Ks1kI8lmOeUm1/6Vo/Cx29PHdhTJrvlvwOUKpNEFfS9OM4ozqsQeIyqcHO3098ovjNfRrW X-Gm-Message-State: AOJu0YxjNvn6Lp2OYRbyH8D4W45pCt1D6sEB/MuVdMiEOzE9EfjTpXQQ I2TTzCTp+DDY7LtoxQefaNMxOvzzz09uQUMCFTiL4UMFSD7c6NuE X-Google-Smtp-Source: AGHT+IF/g+iCJT8gjvG25jUyhrUZH0JrxEIa4asXMTOKU7E3IlhCiusL8Gnrk+EpRxwMbm4GkBA4RQ== X-Received: by 2002:a17:90a:70c6:b0:2c8:87e:c2d9 with SMTP id 98e67ed59e1d1-2ca35d43887mr6411276a91.39.1720698560783; Thu, 11 Jul 2024 04:49:20 -0700 (PDT) Received: from [192.168.255.10] ([43.132.141.20]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2ca34e6e9c3sm5518047a91.20.2024.07.11.04.49.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Jul 2024 04:49:20 -0700 (PDT) Message-ID: <9b1384e7-e75d-4d71-8798-0d47c33cece6@gmail.com> Date: Thu, 11 Jul 2024 19:49:15 +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: [REF PATCH v3 2/2] mm/slab: decouple the SLAB_OBJ_EXT from MEMCG To: Vlastimil Babka , alexs@kernel.org, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Randy Dunlap , Yoann Congal , Masahiro Yamada , Petr Mladek , Suren Baghdasaryan References: <20240710054336.190410-1-alexs@kernel.org> <20240710054336.190410-2-alexs@kernel.org> Content-Language: en-US From: Alex Shi In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/11/24 4:11 PM, Vlastimil Babka wrote: > On 7/10/24 7:43 AM, alexs@kernel.org wrote: >> From: "Alex Shi (Tencent)" >> >> commit 21c690a349ba ("mm: introduce slabobj_ext to support slab object >> extensions") selected SLAB_OBJ_EXT on MEMCG just for SLAB_MATCH >> memcg_data, that included SLAB_OBJ_EXT for MEMCG. In fact, I didn't see >> the necessary to enable SLAB_OBJ_EXT for MEMCG. >> >> Let's decouple the SLAB_OBJ_EXT from MEMCG and move out >> alloc_slab_obj_exts() definition from SLAB_OBJ_EXT only. To alignment >> the alloc_slab_obj_exts() return 0 for good. change its return value to >> '-1' for always failed with !SLAB_OBJ_EXT. Now we could save unnecessary >> code from MEMCG but !SLAB_OBJ_EXT. >> >> Signed-off-by: Alex Shi (Tencent) > > This seems just wrong to me. The memcg hooks for slab do use obj_ext. You > made alloc_slab_obj_exts() return -1 and that will just fail all memcg > charging (unless alloc profiling selects obj_ext). The kernel will appear to > work, but memcg charging for slab won't happen at all. > > So no, it can't be decoupled for slab, only for pages/folios (patch 1). Hi Vlastimil, Thanks a lot for clarification! Yes, the patch isn't correct. Just forgive my stupidity, why the memcg needs SLAB_OBJ_EXT? And why we need to alloc_slab_obj_exts() at line 3019 with !slab_obj_exts? 3015 for (i = 0; i < size; i++) { 3016 slab = virt_to_slab(p[i]); 3017 3018 if (!slab_obj_exts(slab) && 3019 alloc_slab_obj_exts(slab, s, flags, false)) { 3020 obj_cgroup_uncharge(objcg, obj_full_size(s)); 3021 continue; 3022 } Thanks! Alex > > >> Cc: Randy Dunlap >> Cc: Yoann Congal >> Cc: Masahiro Yamada >> Cc: Petr Mladek >> --- >> init/Kconfig | 1 - >> mm/slab.h | 6 +++--- >> mm/slub.c | 6 +++--- >> 3 files changed, 6 insertions(+), 7 deletions(-) >> >> diff --git a/init/Kconfig b/init/Kconfig >> index 26bf8bb0a7ce..61e43ac9fe75 100644 >> --- a/init/Kconfig >> +++ b/init/Kconfig >> @@ -965,7 +965,6 @@ config MEMCG >> bool "Memory controller" >> select PAGE_COUNTER >> select EVENTFD >> - select SLAB_OBJ_EXT >> help >> Provides control over the memory footprint of tasks in a cgroup. >> >> diff --git a/mm/slab.h b/mm/slab.h >> index 8ffdd4f315f8..6c727ecc1068 100644 >> --- a/mm/slab.h >> +++ b/mm/slab.h >> @@ -559,9 +559,6 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab) >> return (struct slabobj_ext *)(obj_exts & ~OBJEXTS_FLAGS_MASK); >> } >> >> -int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, >> - gfp_t gfp, bool new_slab); >> - >> #else /* CONFIG_SLAB_OBJ_EXT */ >> >> static inline struct slabobj_ext *slab_obj_exts(struct slab *slab) >> @@ -571,6 +568,9 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab) >> >> #endif /* CONFIG_SLAB_OBJ_EXT */ >> >> +int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, >> + gfp_t gfp, bool new_slab); >> + >> static inline enum node_stat_item cache_vmstat_idx(struct kmem_cache *s) >> { >> return (s->flags & SLAB_RECLAIM_ACCOUNT) ? >> diff --git a/mm/slub.c b/mm/slub.c >> index cc11f3869cc6..f531c2d67238 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -2075,10 +2075,10 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, >> >> #else /* CONFIG_SLAB_OBJ_EXT */ >> >> -static int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, >> - gfp_t gfp, bool new_slab) >> +int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, >> + gfp_t gfp, bool new_slab) >> { >> - return 0; >> + return -1; >> } >> >> static inline void free_slab_obj_exts(struct slab *slab) >