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: 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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a99d504..753df01 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1634,7 +1634,8 @@
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 @@
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 @@
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;