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Commit d630dc4c authored by Tejun Heo's avatar Tejun Heo
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percpu-refcount: one bit is enough for REF_STATUS 



percpu-refcount currently reserves two lowest bits of its percpu
pointer to indicate its state; however, only one bit is used for
PCPU_REF_DEAD.

Simplify it by removing PCPU_STATUS_BITS/MASK and testing
PCPU_REF_DEAD directly.  This also allows the compiler to choose a
more efficient instruction depending on the architecture.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
parent 55c6c814

include/linux/percpu-refcount.h

+1 −3
Original line number Diff line number Diff line
@@ -88,12 +88,10 @@ static inline void percpu_ref_kill(struct percpu_ref *ref) 
	return percpu_ref_kill_and_confirm(ref, NULL);

}



#define PCPU_STATUS_BITS	2

#define PCPU_STATUS_MASK	((1 << PCPU_STATUS_BITS) - 1)

#define PCPU_REF_PTR		0

#define PCPU_REF_DEAD		1



#define REF_STATUS(count)	(((unsigned long) count) & PCPU_STATUS_MASK)

#define REF_STATUS(count)	(((unsigned long) count) & PCPU_REF_DEAD)



/**

 * percpu_ref_get - increment a percpu refcount

lib/percpu-refcount.c

+1 −1
Original line number Diff line number Diff line
@@ -96,7 +96,7 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu) 


	/* Mask out PCPU_REF_DEAD */

	pcpu_count = (unsigned __percpu *)

		(((unsigned long) pcpu_count) & ~PCPU_STATUS_MASK);

		(((unsigned long) pcpu_count) & ~PCPU_REF_DEAD);



	for_each_possible_cpu(cpu)

		count += *per_cpu_ptr(pcpu_count, cpu);