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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
Download patch file Download diff file Expand all files Collapse all files

7
kernel/cgroup.c
View file

@ -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;