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From: Hao Li To: "Vlastimil Babka (SUSE)" Cc: Harry Yoo , Suren Baghdasaryan , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH v3 08/13] mm/slab: change struct slabobj_ext to a union Message-ID: References: <20260727-b4-objext_split-v3-0-c29ef0f1f257@kernel.org> <20260727-b4-objext_split-v3-8-c29ef0f1f257@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260727-b4-objext_split-v3-8-c29ef0f1f257@kernel.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: AF221100010 X-Rspam-User: X-Stat-Signature: 4utdiuthzg15opui6d6rrobwusifhrqd X-Rspamd-Server: rspam04 X-HE-Tag: 1785411608-444293 X-HE-Meta: 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 V57Gper5 eKV7AF7ZZ0cI2VBjZxWQO68CzY9uhxlZpR3SR36uaN9Jw/FRS2hoOKi0znbZ+9Ax07OjZlTOgN1igQsXRdIdx+StJwfrCEPK77PMOxMwexeYj0SQmvahW0Ex0f9dgzV3XnOP0S2RsxwrqFno5AEF8tOJlpOhXujckDymcgropyzAtjqXejdc48MvgS03wdfOA29tZVgTf+1ukAMNWU/5jYzb1kZUYWac3mweywrPP4ynUnVYtCEltw4QIYJgRjfiEYzJL6dDqKruDYzb0C4EY8y/r2qiNED9MBCcXyA32a7GlVFE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 27, 2026 at 02:54:02PM +0200, Vlastimil Babka (SUSE) wrote: > Currently, struct slabobj_ext can hold both objcg pointer and > codetag_ref (when both are compile-enabled) and there is an array of as > many slabobj_ext instances as there are objects in a slab. > > This makes the layout fixed so even if codetag_ref is unused (because > memory allocation profiling is disabled), the space for them is > allocated and wasted. Similarly, some caches (currently kmalloc_normal) > do not ever need objcg pointers, leading to wasted memory with memory > allocation profiling enabled. > > To make this more flexible, change the layout so that struct slabobj_ext > becomes a union of objcg pointer and codetag_ref (to ensure uniform > size; in practice both are the same size anyway). The slabobj_ext array > then can have twice as many elements as before. For cache locality > purposes, the effective memory layout is unchanged, so objcg and codetag > ref for a given object are still adjacent. > > cache_obj_ext_size() returns the effective size of (0-2) struct > slabobj_ext's for a cache, slab_obj_ext_size() for a slab. Currently > both return a constant value derived from the config options, but will > be made dynamic later. Replace all sizeof(slabobj_ext) usage with these. > > No functional change intended, the layout is still effectively static. > > Reviewed-by: Suren Baghdasaryan > Signed-off-by: Vlastimil Babka (SUSE) > --- LGTM. Reviewed-by: Hao Li -- Thanks, Hao