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X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770959895-817666 X-HE-Meta: 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 ZiNGmmXs RxoEAd84BfIL5KC43D84Eo7Wfxb880mrNkjV79wjTYLmj2QrfuS2+D8A8zqAA0hzWm0JxMgPSGQL17QQX0wwDHKFI+Y9Vgoyg7A+OM9Uh7ZjDRT97pw75t8JG1RE1fCHjWWv/Ydsy+2UI1U41xVKvqi15QkAF8eYiXXZmuDwnrPUv1RtwSZUoPIbAaDCb+fCHdAp/HHbn6AAAyJE= 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 Thu, Feb 12, 2026 at 12:52:46PM +0100, Vlastimil Babka wrote: > On 2/11/26 11:16, Uladzislau Rezki wrote: > > On Fri, Feb 06, 2026 at 06:34:04PM +0900, Harry Yoo wrote: > >> k[v]free_rcu() repurposes two fields of struct rcu_head: 'func' to store > >> the start address of the object, and 'next' to link objects. > >> > >> However, using 'func' to store the start address is unnecessary: > >> > >> 1. slab can get the start address from the address of struct rcu_head > >> field via nearest_obj(), and > >> > >> 2. vmalloc and large kmalloc can get the start address by aligning > >> down the address of the struct rcu_head field to the page boundary. > >> > >> Therefore, allow an 8-byte (on 64-bit) field (of a new type called > >> struct rcu_ptr) to be used with k[v]free_rcu() with two arguments. > >> > >> Some users use both call_rcu() and k[v]free_rcu() to process callbacks > >> (e.g., maple tree), so it makes sense to have struct rcu_head field > >> to handle both cases. However, many users that simply free objects via > >> kvfree_rcu() can save one pointer by using struct rcu_ptr instead of > >> struct rcu_head. > >> > >> Note that struct rcu_ptr is a single pointer only when > >> CONFIG_KVFREE_RCU_BATCHED=y. To keep kvfree_rcu() implementation minimal > >> when CONFIG_KVFREE_RCU_BATCHED is disabled, struct rcu_ptr is the size > >> as struct rcu_head, and the implementation of kvfree_rcu() remains > >> unchanged in that configuration. > > Won't that be too limiting, if we can't shrink structures (e.g. BPF) > unconditionally? Or acceptable because CONFIG_KVFREE_RCU_BATCHED=n is uncommon? I thought BPF would be the primary user of this feature, and I believe anyone that cares about BPF performance / memory usage will use CONFIG_KVFREE_RCU_BATCHED=y. But yeah, if we have more users of this feature beyond BPF, it makes sense to reduce memory usage for CONFIG_KVFREE_RCU_BATCHED=n users with some complexity. -- Cheers, Harry / Hyeonggon