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percpu-refcount: one bit is enough for REF_STATUS

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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: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
This commit is contained in:
Tejun Heo 2014-06-28 08:10:12 -04:00
parent 55c6c814ae
commit d630dc4c9a
2 changed files with 2 additions and 4 deletions
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4
include/linux/percpu-refcount.h
View File

@ -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

2
lib/percpu-refcount.c
View File

@ -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);