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b=IpxI1fdeSQBhQ7ZGkZTOQuEPFZ1TJ0B2VthQ6AR1k2WBwOxcLW6xhTzugez/mIXl+ 3slTyE1QclugptWka4V4JXZEIYAtgRXs2McJ0TkrqXBa03tzwCZRqBM2RWxMytuoZ3 a+vyKk1lYyz7GpETh0gE6dWYdAukTd+DAPurvHH6AKAx6O4QkmkfljI+mmeBhMmYC1 c/Jb4yxlVAZnwkikwLRjPPogjtp9qq/YkV7WvCGRb+8D1sLiZPrxFiCbq0fYtGyeEg mjYzeHIBngZ1ARgMlNMrK6xl0Kqn+uqqY+e7yxC7hFkGh2Nb6agsDTpPg5rT4LyiAf lzwZL12gZ/sWg== Date: Wed, 29 Jul 2026 06:18:44 +0000 From: Harry Yoo To: "Vlastimil Babka (SUSE)" Cc: Suren Baghdasaryan , Hao Li , 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 06/13] mm/slab: abstract slabobj_ext.ref access Message-ID: References: <20260727-b4-objext_split-v3-0-c29ef0f1f257@kernel.org> <20260727-b4-objext_split-v3-6-c29ef0f1f257@kernel.org> <365d8e50-5aeb-45e9-97a3-87d0024cdc5f@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <365d8e50-5aeb-45e9-97a3-87d0024cdc5f@kernel.org> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6B4F380008 X-Rspam-User: X-Stat-Signature: 31hp81nx8ufputgqhxuab8qqmkby17ja X-HE-Tag: 1785305928-598481 X-HE-Meta: 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 IIPBdYQx 5Wxcc/PSmgYRD7NfFp+gMZe4B6vIxOeRaWa6gDetNvRsWEqpz7RCr7AJK5m2wqoJHbGilm1/YbcZKHTt+wrh+uSPYea/QNWEi6RvhBAaV/AT2z6u3CgcIFQ7koVn65A2xnVaEuYEJVigOJ0NsE6cLVoK6wRBlAccloMzzzLm9J9ipF3pCw52YBDGCwVElvRxFoqog4/NGgOrfTVr22qJEXit2iDM9v66npTWoRLkvOL/C4SMx7VZZ9hQZBfmdC1if6VkstHQhnTG2wACxFEcW2Y0d30eJniUZa/3XUwX4I5LGcbH5J69eDI9sBX/WNf5ZGsr55QES3tpZDH88Qbq29SsNIqvnhdoRxoYS Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 28, 2026 at 07:41:15PM +0200, Vlastimil Babka (SUSE) wrote: > On 7/28/26 15:41, Harry Yoo wrote: > > On Mon, Jul 27, 2026 at 02:54:00PM +0200, Vlastimil Babka (SUSE) wrote: > >> In preparation for changes to the structure, abstract access to the ref > >> field with a slab_obj_ext_codetag_ref() function. Rename the field to > >> _ctref to make an unexpected direct access a compile error. > >> > >> No functional change intended. > >> > >> Reviewed-by: Suren Baghdasaryan > >> Reviewed-by: Hao Li > >> Signed-off-by: Vlastimil Babka (SUSE) > >> --- > > > > Looks good to me, > > Reviewed-by: Harry Yoo (Oracle) > > > > With a suggestion: it would be nice to have debug warnings > > that trigger when slab_obj_ext_codetag_ref() is compiled but > > not supposed to be called. > > > > e.g.) for kfence objects, or later in the series when we > > reduce slabobj_ext memory (!slab_obj_ext_has_codetag()) > > > > Similarly, it would be nice (later in the series) to have a warning > > in slab_obj_ext_objcg() when slab_needs_objcg() returns false. > > OK good idea but we can't do it right now as the helpers are introduced > later. > > So for 9/13 mm/slab: introduce slab_obj_ext_has_codetag(): > > diff --git a/mm/slab.h b/mm/slab.h > index 8f352d9f4d91..fbad99da093c 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -726,6 +726,8 @@ static inline void slab_obj_ext_set_objcg(struct slabobj_ext *obj_ext, > static inline union codetag_ref * > slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext) > { > + VM_WARN_ON_ONCE(!slab_obj_ext_has_codetag()); > + > if (IS_ENABLED(CONFIG_MEMCG)) > obj_ext += 1; > > ... and for objcg we would need to start passing slab pointer to > slab_obj_ext_objcg() and slab_obj_ext_set_objcg(). Hmm... But slab_obj_ext_codetag_ref() already takes the parameter to calculate offset. I think it's worth as it'll be optimized away on non-debug kerenels and there is no way to detect type confusion due to subtle errors in the objext layout.