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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) <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>
zero-sugar-mainline-defconfig
Uladzislau Rezki (Sony) 2020-05-25 23:47:59 +02:00 committed by Paul E. McKenney
parent 3042f83f19
commit 1835f475e3
1 changed files with 34 additions and 4 deletions
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38
include/linux/rcupdate.h
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@ -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