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rcu: Support reclaim for head-less object

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Update the kvfree_call_rcu() function with head-less support.
This allows RCU to reclaim objects without an embedded rcu_head.

tree-RCU:
We introduce two chains of arrays to store SLAB-backed and vmalloc
pointers, each.  Storage in either of these arrays does not require
embedding an rcu_head within the object.

Maintaining the arrays may become impossible due to high memory
pressure. For such cases there is an emergency path. Objects with
rcu_head inside are just queued on a backup rcu_head list. Later on
that list is drained. As for the head-less variant, as the current
context can sleep, the following emergency measures are applied:
   a) Synchronously wait until a grace period has elapsed.
   b) Call kvfree().

tiny-RCU:
For double argument calls, there are no new changes in behavior. For
single argument call, kvfree() is directly inlined on the current
stack after a synchronize_rcu() call. Note that for tiny-RCU, any
call to synchronize_rcu() is actually a quiescent state, therefore
it does nothing.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Co-developed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Uladzislau Rezki (Sony)
2020-05-25 23:47:58 +02:00
committed by Paul E. McKenney
parent ce4dce123f
commit 3042f83f19
2 changed files with 60 additions and 3 deletions
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18
include/linux/rcutiny.h
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@@ -34,9 +34,25 @@ static inline void synchronize_rcu_expedited(void)
synchronize_rcu();
}
/*
* Add one more declaration of kvfree() here. It is
* not so straight forward to just include <linux/mm.h>
* where it is defined due to getting many compile
* errors caused by that include.
*/
extern void kvfree(const void *addr);
static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
{
call_rcu(head, func);
if (head) {
call_rcu(head, func);
return;
}
// kvfree_rcu(one_arg) call.
might_sleep();
synchronize_rcu();
kvfree((void *) func);
}
void rcu_qs(void);