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Wed, 05 Feb 2025 01:13:45 -0800 (PST) Date: Wed, 5 Feb 2025 18:13:37 +0900 From: "Harry (Hyeonggon) Yoo" <42.hyeyoo@gmail.com> To: Vlastimil Babka Cc: Christoph Lameter , David Rientjes , "Paul E. McKenney" , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Andrew Morton , Roman Gushchin , linux-mm@kvack.org, Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , rcu@vger.kernel.org Subject: Re: [PATCH 3/4] rcu, slab: use a regular callback function for kvfree_rcu Message-ID: References: <20250203-slub-tiny-kfree_rcu-v1-0-d4428bf9a8a1@suse.cz> <20250203-slub-tiny-kfree_rcu-v1-3-d4428bf9a8a1@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250203-slub-tiny-kfree_rcu-v1-3-d4428bf9a8a1@suse.cz> X-Stat-Signature: jjhjgce9bjcidcjfnoy77fy9orooqrk4 X-Rspamd-Queue-Id: EC4981C000F X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1738746827-100550 X-HE-Meta: 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 As+2B281 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 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 Mon, Feb 03, 2025 at 10:28:49AM +0100, Vlastimil Babka wrote: > RCU has been special-casing callback function pointers that are integers > lower than 4096 as offsets of rcu_head for kvfree() instead. The tree > RCU implementation no longer does that as the batched kvfree_rcu() is > not a simple call_rcu(). The tiny RCU still does, and the plan is also > to make tree RCU use call_rcu() for SLUB_TINY configurations. > > Instead of teaching tree RCU again to special case the offsets, let's > remove the special casing completely. Since there's no SLOB anymore, it > is possible to create a callback function that can take a pointer to a > middle of slab object with unknown offset and determine the object's > pointer before freeing it, so implement that as kvfree_rcu_cb(). > > Large kmalloc and vmalloc allocations are handled simply by aligning > down to page size. For that we retain the requirement that the offset is > smaller than 4096. But we can remove __is_kvfree_rcu_offset() completely > and instead just opencode the condition in the BUILD_BUG_ON() check. > > Reviewed-by: Joel Fernandes (Google) Looks good to me, Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> > Signed-off-by: Vlastimil Babka -- Harry