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Wed, 7 Jan 2026 14:56:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id CG4qNSl0XmmzXwAAD6G6ig (envelope-from ); Wed, 07 Jan 2026 14:56:41 +0000 Message-ID: <473d479c-4eae-4589-b8c2-e2a29e8e6bc1@suse.cz> Date: Wed, 7 Jan 2026 15:56:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V5 4/8] mm/slab: abstract slabobj_ext access via new slab_obj_ext() helper Content-Language: en-US To: Harry Yoo , akpm@linux-foundation.org Cc: andreyknvl@gmail.com, cl@gentwo.org, dvyukov@google.com, glider@google.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev, rientjes@google.com, roman.gushchin@linux.dev, ryabinin.a.a@gmail.com, shakeel.butt@linux.dev, surenb@google.com, vincenzo.frascino@arm.com, yeoreum.yun@arm.com, tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, hao.li@linux.dev References: <20260105080230.13171-1-harry.yoo@oracle.com> <20260105080230.13171-5-harry.yoo@oracle.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A5ECB140008 X-Stat-Signature: whyqdkgyrc1s5pmqi6igawdonnkxw5fk X-Rspam-User: X-HE-Tag: 1767797803-630100 X-HE-Meta: U2FsdGVkX1/lj4AzhYAfmExlhlCxt0rU927IRd+RYyjWkL3bPUscdPwHX1ZR0L5Pps5KSaVKkl7daN+dxx3XSQxYls1boNYjK7pvtu7AkyXhQHDEJqrlstsvynza9bR2XTchGzPT25crX1HS8SsF1mhMNYuCdCYKVCAWW2gTNQVp2jLJ1HjDKGxuS0ZR3aHTUf2cbWUldQDGRhnlcXqR9N2ceFrFNpzlvTuuuT6CtoDIt0K5EfUHlfYfnVgwqDhJNr/4a9ju9qCWR8e61Y1OVZec5aALBGEbRl3xnzjaJcfcJwfiyDjiwAsbLpJ35tIDiWp7BijrLTluSRwXI7Ix042R5WwdJtfcEbIGcPXaHOkCB5R4QgdViaKAZAH13DbzWzRuTYkGtsB+d2nY64AogZFfD4Ufsik8CSZ9feu5wEqyOOFOieKeRQakR2jEEjJ2WmokjBDUiX8lhmQZsbWCqL+TeOzMCvzBIEEML7G1AE4zyQBobvoW6n180GSckPuqVuWeI1Yc/6HCyiIqwB1gqNgokYYl3Bbef143ZKmVQ6zfZ/Haguw3SrE+c6N7AA5332AF8OoFDH/HJhZwZTphvbvhcNE/kkpIMwq7op/FT+hdzUwam84hlKeXwImFxD8T3DFhR/E3KQJDFC28JL9o+KJwwSsHWVuGo/7FGDvcsnuRgZOqNQZQH38HI7pTuIDB8bSXpaBGXsfvNgJ26unhMF/ajtM7NcTD/ZtX4JBrTWHs2k+RQmRBHVTmJExr3hOSS+2Mp3mu837vxC4GmVNnBVnJH9vYfOtq/V+eTBw8iX0AuqFcIHeQC5u5Y38BcpXSTKwtm9HQc8vtIuoHZ0phJ8CcEphlpAH/MG9NnmMPBUXBUk31XLPpbg+IBDh7OtTrFVTXsNwpLJ5tLHFWRKm0kDij9IOCs2lABuQd1PhMomIjzI+gPekhQjivAr5oceKrf5xOskkQFyZkon5uXCA jdx4NTvk 2yM2SwtbCXQ6AwICY0/ivUXuWvkPm2mLpS/bn8wQ9wIymG03Xv7mo/zRSGTtmPJKcPo7eZEouAqwuIJioUhhE1Y0CXqhk64qU0mgavq5b4dqPvQQya/O8Mnk5PQbSW3aPAhQV1G89KrC3avjsDt4OUtJ49ASjs7Lj6dtfAplzHVHxdcCkqR/yUdPZpWhFoMjbXAaUO1Lf181K/La81cDXHBZSo63BWe03VqvLcMCyMaVM48sWzJ99maB8RJQf9QyTlrbOkOZNE1mVcZcai0io4TDz69D//aiCwrLoqw6m4W7szgk36i3GJ3qVpCj9LEA0oiXxtW4Kg6CKHvxRruOxNzX8Stc9rCwIJjmRQ35bVquDF2mMiuzfiOxjw5pUWzJF1q1AEl6H+Thut1XlVclIlWFfIMuWwov19NhSiJDctFYVZQA1MFSWJFUgokNafCEWe4wF 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 1/5/26 09:02, Harry Yoo wrote: > Currently, the slab allocator assumes that slab->obj_exts is a pointer > to an array of struct slabobj_ext objects. However, to support storage > methods where struct slabobj_ext is embedded within objects, the slab > allocator should not make this assumption. Instead of directly > dereferencing the slabobj_exts array, abstract access to > struct slabobj_ext via helper functions. > > Introduce a new API slabobj_ext metadata access: > > slab_obj_ext(slab, obj_exts, index) - returns the pointer to > struct slabobj_ext element at the given index. > > Directly dereferencing the return value of slab_obj_exts() is no longer > allowed. Instead, slab_obj_ext() must always be used to access > individual struct slabobj_ext objects. > > Convert all users to use these APIs. > No functional changes intended. > > +/* > + * slab_obj_ext - get the pointer to the slab object extension metadata > + * associated with an object in a slab. > + * @slab: a pointer to the slab struct > + * @obj_exts: a pointer to the object extension vector > + * @index: an index of the object > + * > + * Returns a pointer to the object extension associated with the object. > + */ > +static inline struct slabobj_ext *slab_obj_ext(struct slab *slab, > + unsigned long obj_exts, > + unsigned int index) > +{ > + struct slabobj_ext *obj_ext; > + > + VM_WARN_ON_ONCE(!slab_obj_exts(slab)); > + VM_WARN_ON_ONCE(obj_exts != slab_obj_exts(slab)); The first check seems redundant given we have the second one? If we get passed obj_ext 0 and slab_obj_exts() is also 0, it will blow up quickly anyway. > + > + obj_ext = (struct slabobj_ext *)obj_exts; > + return &obj_ext[index]; > } > > int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > @@ -533,7 +558,13 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > > #else /* CONFIG_SLAB_OBJ_EXT */ > > -static inline struct slabobj_ext *slab_obj_exts(struct slab *slab) > +static inline unsigned long slab_obj_exts(struct slab *slab) > +{ > + return 0; > +} > + > +static inline struct slabobj_ext *slab_obj_ext(struct slab *slab, > + unsigned int index) Hmm this is missing the obj_exts parameter? Either will not compile !CONFIG_SLAB_OBJ_EXT or isn't reachable in that config anyway? > { > return NULL; > } > @@ -550,7 +581,7 @@ static inline enum node_stat_item cache_vmstat_idx(struct kmem_cache *s) > bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, > gfp_t flags, size_t size, void **p); > void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, > - void **p, int objects, struct slabobj_ext *obj_exts); > + void **p, int objects, unsigned long obj_exts); > #endif > > void kvfree_rcu_cb(struct rcu_head *head); > diff --git a/mm/slub.c b/mm/slub.c > index 0e32f6420a8a..84bd4f23dc4a 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2176,7 +2178,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > > static inline void free_slab_obj_exts(struct slab *slab) > { > - struct slabobj_ext *obj_exts; > + unsigned long obj_exts; I think in this function we could leave it as pointer. > obj_exts = slab_obj_exts(slab); And do a single cast here. > if (!obj_exts) { > @@ -2196,11 +2198,11 @@ static inline void free_slab_obj_exts(struct slab *slab) > * NULL, therefore replace NULL with CODETAG_EMPTY to indicate that > * the extension for obj_exts is expected to be NULL. > */ > - mark_objexts_empty(obj_exts); > + mark_objexts_empty((struct slabobj_ext *)obj_exts); > if (unlikely(READ_ONCE(slab->obj_exts) & OBJEXTS_NOSPIN_ALLOC)) > - kfree_nolock(obj_exts); > + kfree_nolock((void *)obj_exts); > else > - kfree(obj_exts); > + kfree((void *)obj_exts); > slab->obj_exts = 0; > } And avoid those 3 above. Unless it gets more complicated with later patches...