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From: Hao Li To: Harry Yoo Cc: Vlastimil Babka , akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] slub: let need_slab_obj_exts() return false if SLAB_NO_OBJ_EXT is set Message-ID: References: <20260205120709.425719-1-hao.li@linux.dev> <67ebb9f2-b383-4b68-949e-239d8c7b18f0@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7A3D2180008 X-Stat-Signature: qczy6pxdp747pymh6f8optk75fh6bzeq X-HE-Tag: 1770377716-159798 X-HE-Meta: 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 g9yc7/8L bQCeAmxvTSlT+ic/bPKOxsQCPmmN24A3G9/fNF4BvTBwuSca6e++wcVT380F6V4wfvwjib4u9zaTC7qzrsiFo2ul5TeFsOFs595rKldI+Pmvl3lhU/4HL33Sd56bYbnMM5dZShDv0C8ZJZ6ZWm9BCpzc+tSgxELNreu1GdUX/a3HMjx/Ugb/dVjXAUVBHAQaa6Q5lRnMJvMnT44P/Aqmx8rWPAQ5rGoWg0vXCwrVolb3PRF/z7J9/tGcnWxqiiJzy+dhonZhpN9Uz2DzX3WH2UMKrlg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Feb 06, 2026 at 07:21:29PM +0900, Harry Yoo wrote: > On Fri, Feb 06, 2026 at 11:03:08AM +0100, Vlastimil Babka wrote: > > On 2/6/26 11:01, Harry Yoo wrote: > > > On Fri, Feb 06, 2026 at 10:40:54AM +0100, Vlastimil Babka wrote: > > >> On 2/6/26 01:53, Harry Yoo wrote: > > >> > On Thu, Feb 05, 2026 at 08:07:23PM +0800, Hao Li wrote: > > >> >> SLAB_NO_OBJ_EXT is set for boot caches, but need_slab_obj_exts() doesn't > > >> >> check this flag. We should return false unconditionally when > > >> >> SLAB_NO_OBJ_EXT is set. > > >> >> > > >> >> Signed-off-by: Hao Li > > >> >> --- > > >> > > > >> > Looks reasonable to me, > > >> > Acked-by: Harry Yoo > > >> > > >> Thanks, added to slab/for-7.0/obj_metadata > > >> I think it doesn't change anything at the moment? > > > > > > ...unless you enable memory allocation profiling :) > > > > If I do, would kmem_cache or kmem_cache_node caches gotten obj_exts in > > leftover space? > > /me builds and tests a new kernel with mem profiling always enabled... > > Yes, but only if merging is disabled. > > If you disable slab merging with `slab_nomerge`, kmem_cache gets > obj_exts from SLAB_OBJ_EXTS_IN_OBJ. > > When I enable debug feature slab_debug=P (and thus change s->size), > kmem_cache_node gets obj_exts from SLAB_OBJ_EXTS_IN_OBJ. Thanks for testing, this matches what I've seen too. Besides, even if the two boot caches, kmem_cache and kmem_cache_node, go through the SLAB_OBJ_EXT_IN_OBJ path, it seems it wouldn't cause real trouble. We'd just end up doing some unnecessary memset. So, as Vlastimil said, this patch is mostly about doing the right thing. -- Thanks, Hao > > -- > Cheers, > Harry / Hyeonggon