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Thu, 12 Nov 2026 07:54:44 +0000 X-Mizu-Trace-ID: 30a148ff905e7f1e X-Migadu-Flow: FLOW_OUT Date: Thu, 12 Nov 2026 15:54:34 +0800 From: Hao Li To: "Vlastimil Babka (SUSE)" Cc: harry@kernel.org, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Suren Baghdasaryan Subject: Re: [PATCH] mm/slab: don't set SLAB_MAY_ACCOUNT for KMALLOC_PARTITION_CACHES Message-ID: References: <20261111125628.375624-1-hao.li@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: byxf46y68zckhhubajr6y6g3439eykz8 X-Rspamd-Queue-Id: 479B2C0009 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794470086-126065 X-HE-Meta: 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 oBtmZOF3 TVB1ADekpoug6yseVaKw9yCa1CPWRG2fxTeF1A2EMecNsGoynUvXGMa9N563KoysocHiTTtalY0cxViTk0FAc8voO7IceY7fMeUXlKXdI2NSi2bfMK+RrU8IIjym5vrFvKByw1vntjPWNkvfKY+6BGzUE+PX5xtCBrsakbQRTX1qiPFRaDRCLIFRQUrfLPmdJAjsnkX2yU0L38pNbf0WEwX7/uC6FXcyyLjY7zAEX2NH2l+veyxvhtnMgz7hHpCmKJ1gUEk6WQNddDcdemr4XFLsZtxgPnNyy/ElEmN4hFwwEGubG8PyVHr/o/BAsw9/vf65z2Ys8VvLljv5BbfbBETfyoQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Nov 11, 2026 at 02:08:40PM +0100, Vlastimil Babka (SUSE) wrote: > On 11/11/26 13:49, Hao Li wrote: > > An allocation with __GFP_ACCOUNT set (without __GFP_DMA or > > __GFP_RECLAIMABLE) is redirected to KMALLOC_CGROUP and will never hit > > KMALLOC_NORMAL or KMALLOC_PARTITION_CACHES. Consequently, neither of > > these caches requires objcg slots in obj_exts. > > > > While KMALLOC_NORMAL already skips setting SLAB_MAY_ACCOUNT, > > KMALLOC_PARTITION_CACHES still carries it unnecessarily. > > > > Extend the check to skip KMALLOC_PARTITION_CACHES as well, saving > > unnecessary objcg slots in obj_exts. > > > > Signed-off-by: Hao Li > > Reviewed-by: Vlastimil Babka (SUSE) Thanks! > > > --- > > This doesn't seem like a real bug to me, just a small waste of memory, so I > > didn't add a Fixes tag. > > Hmm I'd add > Fixes: 7def2e8549e5 ("mm/slab: add cache_ and slab_needs_objcg() helpers") Ah right, I mixed up Fixes with cc stable. Thanks for pointing it out! > > The question is whether cc stable as well. 7.3 LTS will be used for Android > and IIRC they have memory allocation profiling enabled. Not sure about > kmalloc partitions. Cc'ing Suren. Makes sense. If Android uses partitioned caches, then it looks like we should cc stable. > > > --- > > mm/slab_common.c | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/mm/slab_common.c b/mm/slab_common.c > > index 2befd24b4d09..f0ea1fa178e7 100644 > > --- a/mm/slab_common.c > > +++ b/mm/slab_common.c > > @@ -1000,16 +1000,18 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type) > > #endif > > > > /* > > - * If memcg_kmem is enabled and this is a KMALLOC_NORMAL cache and not > > - * aliased with any other type, make sure it's never merged with any other > > - * cache. > > + * If memcg_kmem is enabled and this is a KMALLOC_NORMAL or > > + * KMALLOC_PARTITION_CACHES cache and not aliased with any other type, > > + * make sure it's never merged with any other cache. > > * > > * In other cases the kmalloc cache may end up being used for a > > * __GFP_ACCOUNT allocation so mark it as such. The exception is a > > * KMALLOC_NO_OBJ_EXT cache. > > */ > > if (!mem_cgroup_kmem_disabled()) { > > - if (type == KMALLOC_NORMAL && KMALLOC_RECLAIM != KMALLOC_NORMAL) > > + if (type >= KMALLOC_PARTITION_START && > > + type <= KMALLOC_PARTITION_END && > > + KMALLOC_RECLAIM != KMALLOC_NORMAL) > > flags |= SLAB_NO_MERGE; > > else if (!(flags & SLAB_NO_OBJ_EXT)) > > flags |= SLAB_MAY_ACCOUNT; >