From 1835f475e3518ade61e25a57572c78b953778656 Mon Sep 17 00:00:00 2001 From: "Uladzislau Rezki (Sony)" Date: Mon, 25 May 2020 23:47:59 +0200 Subject: [PATCH] rcu: Introduce single argument kvfree_rcu() interface 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) Reviewed-by: Joel Fernandes (Google) Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 51b26ab..d15d46d 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -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 -- 2.7.4