rcu: Introduce single argument kvfree_rcu() interface (1835f475) · Commits · 戴 / test

Make kvfree_rcu() capable of freeing objects that will not embed an rcu_head within it. This saves storage overhead in such objects. Reclaiming headless objects this way requires only a single argument (pointer to the object). After this patch, there are two ways to use kvfree_rcu(): a) kvfree_rcu(ptr, rhf); struct X { struct rcu_head rhf; unsigned char data[100]; }; void *ptr = kvmalloc(sizeof(struct X), GFP_KERNEL); if (ptr) kvfree_rcu(ptr, rhf); b) kvfree_rcu(ptr); void *ptr = kvmalloc(some_bytes, GFP_KERNEL); if (ptr) kvfree_rcu(ptr); Note that the headless usage (example b) can only be used in a code that can sleep. This is enforced by the CONFIG_DEBUG_ATOMIC_SLEEP option. Co-developed-by:

Joel Fernandes (Google) <joel@joelfernandes.org> Reviewed-by:

Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by:

Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

include/linux/rcupdate.h

+34 −4

Original line number	Diff line number	Diff line
		@@ -877,12 +877,42 @@ do { \

		/**
		* kvfree_rcu() - kvfree an object after a grace period.
		* @ptr: pointer to kvfree
		* @rhf: the name of the struct rcu_head within the type of @ptr.
		*
		* Same as kfree_rcu(), just simple alias.
		* This macro consists of one or two arguments and it is
		* based on whether an object is head-less or not. If it
		* has a head then a semantic stays the same as it used
		* to be before:
		*
		* kvfree_rcu(ptr, rhf);
		*
		* where @ptr is a pointer to kvfree(), @rhf is the name
		* of the rcu_head structure within the type of @ptr.
		*
		* When it comes to head-less variant, only one argument
		* is passed and that is just a pointer which has to be
		* freed after a grace period. Therefore the semantic is
		*
		* kvfree_rcu(ptr);
		*
		* where @ptr is a pointer to kvfree().
		*
		* Please note, head-less way of freeing is permitted to
		* use from a context that has to follow might_sleep()
		* annotation. Otherwise, please switch and embed the
		* rcu_head structure within the type of @ptr.
		*/
		#define kvfree_rcu(ptr, rhf) kfree_rcu(ptr, rhf)
		#define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \
		kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)

		#define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
		#define kvfree_rcu_arg_2(ptr, rhf) kfree_rcu(ptr, rhf)
		#define kvfree_rcu_arg_1(ptr) \
		do { \
		typeof(ptr) ___p = (ptr); \
		\
		if (___p) \
		kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \
		} while (0)

		/*
		* Place this after a lock-acquisition primitive to guarantee that

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