Re: [PATCH 3/4] rcu, slab: use a regular callback function for kvfree_rcu

["Harry (Hyeonggon) Yoo" <42.hyeyoo@gmail.com>]

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) <joel@joelfernandes.org>

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

-- 
Harry