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percpu_ref: add PERCPU_REF_INIT_* flags

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With the recent addition of percpu_ref_reinit(), percpu_ref now can be
used as a persistent switch which can be turned on and off repeatedly
where turning off maps to killing the ref and waiting for it to drain;
however, there currently isn't a way to initialize a percpu_ref in its
off (killed and drained) state, which can be inconvenient for certain
persistent switch use cases.

Similarly, percpu_ref_switch_to_atomic/percpu() allow dynamic
selection of operation mode; however, currently a newly initialized
percpu_ref is always in percpu mode making it impossible to avoid the
latency overhead of switching to atomic mode.

This patch adds @flags to percpu_ref_init() and implements the
following flags.

* PERCPU_REF_INIT_ATOMIC	: start ref in atomic mode
* PERCPU_REF_INIT_DEAD		: start ref killed and drained

These flags should be able to serve the above two use cases.

v2: target_core_tpg.c conversion was missing.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
This commit is contained in:
Tejun Heo
2014-09-24 13:31:50 -04:00
parent f47ad45784
commit 2aad2a86f6
6 changed files with 43 additions and 13 deletions
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23
lib/percpu-refcount.c
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@@ -45,27 +45,40 @@ static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
* percpu_ref_init - initialize a percpu refcount
* @ref: percpu_ref to initialize
* @release: function which will be called when refcount hits 0
* @flags: PERCPU_REF_INIT_* flags
* @gfp: allocation mask to use
*
* Initializes the refcount in single atomic counter mode with a refcount of 1;
* analagous to atomic_long_set(ref, 1).
* Initializes @ref. If @flags is zero, @ref starts in percpu mode with a
* refcount of 1; analagous to atomic_long_set(ref, 1). See the
* definitions of PERCPU_REF_INIT_* flags for flag behaviors.
*
* Note that @release must not sleep - it may potentially be called from RCU
* callback context by percpu_ref_kill().
*/
int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
gfp_t gfp)
unsigned int flags, gfp_t gfp)
{
size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
__alignof__(unsigned long));
atomic_long_set(&ref->count, 1 + PERCPU_COUNT_BIAS);
unsigned long start_count = 0;
ref->percpu_count_ptr = (unsigned long)
__alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
if (!ref->percpu_count_ptr)
return -ENOMEM;
if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
else
start_count += PERCPU_COUNT_BIAS;
if (flags & PERCPU_REF_INIT_DEAD)
ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
else
start_count++;
atomic_long_set(&ref->count, start_count);
ref->release = release;
return 0;
}