Commit 2aad2a86 authored by Tejun Heo's avatar Tejun Heo
Browse files

percpu_ref: add PERCPU_REF_INIT_* flags 



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: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarKent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
parent f47ad457

block/blk-mq.c

+1 −1
Original line number Diff line number Diff line
@@ -1796,7 +1796,7 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set) 
		goto err_hctxs;



	if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release,

			    GFP_KERNEL))

			    0, GFP_KERNEL))

		goto err_map;



	setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);

drivers/target/target_core_tpg.c

+1 −1
Original line number Diff line number Diff line
@@ -819,7 +819,7 @@ int core_tpg_add_lun( 
{

	int ret;



	ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release,

	ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release, 0,

			      GFP_KERNEL);

	if (ret < 0)

		return ret;

fs/aio.c

+2 −2
Original line number Diff line number Diff line
@@ -661,10 +661,10 @@ static struct kioctx *ioctx_alloc(unsigned nr_events) 


	INIT_LIST_HEAD(&ctx->active_reqs);



	if (percpu_ref_init(&ctx->users, free_ioctx_users, GFP_KERNEL))

	if (percpu_ref_init(&ctx->users, free_ioctx_users, 0, GFP_KERNEL))

		goto err;



	if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, GFP_KERNEL))

	if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, 0, GFP_KERNEL))

		goto err;



	ctx->cpu = alloc_percpu(struct kioctx_cpu);

include/linux/percpu-refcount.h

+17 −1
Original line number Diff line number Diff line
@@ -63,6 +63,21 @@ enum { 
	__PERCPU_REF_FLAG_BITS	= 2,

};



/* @flags for percpu_ref_init() */

enum {

	/*

	 * Start w/ ref == 1 in atomic mode.  Can be switched to percpu

	 * operation using percpu_ref_switch_to_percpu().

	 */

	PERCPU_REF_INIT_ATOMIC	= 1 << 0,



	/*

	 * Start dead w/ ref == 0 in atomic mode.  Must be revived with

	 * percpu_ref_reinit() before used.  Implies INIT_ATOMIC.

	 */

	PERCPU_REF_INIT_DEAD	= 1 << 1,

};



struct percpu_ref {

	atomic_long_t		count;

	/*
@@ -76,7 +91,8 @@ struct percpu_ref { 
};



int __must_check percpu_ref_init(struct percpu_ref *ref,

				 percpu_ref_func_t *release, gfp_t gfp);

				 percpu_ref_func_t *release, unsigned int flags,

				 gfp_t gfp);

void percpu_ref_exit(struct percpu_ref *ref);

void percpu_ref_switch_to_atomic(struct percpu_ref *ref,

				 percpu_ref_func_t *confirm_switch);

kernel/cgroup.c

+4 −3
Original line number Diff line number Diff line
@@ -1634,7 +1634,8 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask) 
		goto out;

	root_cgrp->id = ret;



	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, GFP_KERNEL);

	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,

			      GFP_KERNEL);

	if (ret)

		goto out;
@@ -4510,7 +4511,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss, 


	init_and_link_css(css, ss, cgrp);



	err = percpu_ref_init(&css->refcnt, css_release, GFP_KERNEL);

	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);

	if (err)

		goto err_free_css;
@@ -4583,7 +4584,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, 
		goto out_unlock;

	}



	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, GFP_KERNEL);

	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);

	if (ret)

		goto out_free_cgrp;

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