On Tue, Sep 23, 2014 at 01:55:17AM -0400, Tejun Heo wrote: > 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. > > Signed-off-by: Tejun Heo <t...@kernel.org> > Cc: Kent Overstreet <k...@daterainc.com> > Cc: Jens Axboe <ax...@kernel.dk> > Cc: Christoph Hellwig <h...@infradead.org> > Cc: Johannes Weiner <han...@cmpxchg.org>
Reviewed-by: Kent Overstreet <k...@daterainc.com> > --- > block/blk-mq.c | 2 +- > fs/aio.c | 4 ++-- > include/linux/percpu-refcount.h | 18 +++++++++++++++++- > kernel/cgroup.c | 7 ++++--- > lib/percpu-refcount.c | 24 +++++++++++++++++++----- > 5 files changed, 43 insertions(+), 12 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 702df07..3f6e6f5 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1777,7 +1777,7 @@ 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); > diff --git a/fs/aio.c b/fs/aio.c > index 93fbcc0f..9b6d5d6 100644 > --- a/fs/aio.c > +++ b/fs/aio.c > @@ -666,10 +666,10 @@ 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); > diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h > index e41ca20..5f84bf0 100644 > --- a/include/linux/percpu-refcount.h > +++ b/include/linux/percpu-refcount.h > @@ -61,6 +61,21 @@ enum { > __PERCPU_REF_ATOMIC_DEAD = __PERCPU_REF_ATOMIC | __PERCPU_REF_DEAD, > }; > > +/* @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; > /* > @@ -74,7 +89,8 @@ 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); > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 589b4d8..e2fbcc1 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1628,7 +1628,8 @@ 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; > > @@ -4487,7 +4488,7 @@ 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; > > @@ -4555,7 +4556,7 @@ 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; > > diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c > index 548b19e..74ec33e 100644 > --- a/lib/percpu-refcount.c > +++ b/lib/percpu-refcount.c > @@ -45,27 +45,41 @@ 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) > { > + unsigned long start_count = 0; > + > BUILD_BUG_ON(__PERCPU_REF_ATOMIC_DEAD & > ~(__alignof__(unsigned long) - 1)); > > - atomic_long_set(&ref->count, 1 + PERCPU_COUNT_BIAS); > - > ref->percpu_count_ptr = > (unsigned long)alloc_percpu_gfp(unsigned long, 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; > } > -- > 1.9.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/