cgroup: introduce coalesce css_get() and css_put()
Current css_get() and css_put() increment/decrement css->refcnt one by
one.
This patch add a new function __css_get(), which takes "count" as a arg
and increment the css->refcnt by "count". And this patch also add a new
arg("count") to __css_put() and change the function to decrement the
css->refcnt by "count".
These coalesce version of __css_get()/__css_put() will be used to improve
performance of memcg's moving charge feature later, where instead of
calling css_get()/css_put() repeatedly, these new functions will be used.
No change is needed for current users of css_get()/css_put().
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index d08cfe7..14160b5 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -76,6 +76,12 @@
CSS_REMOVED, /* This CSS is dead */
};
+/* Caller must verify that the css is not for root cgroup */
+static inline void __css_get(struct cgroup_subsys_state *css, int count)
+{
+ atomic_add(count, &css->refcnt);
+}
+
/*
* Call css_get() to hold a reference on the css; it can be used
* for a reference obtained via:
@@ -87,7 +93,7 @@
{
/* We don't need to reference count the root state */
if (!test_bit(CSS_ROOT, &css->flags))
- atomic_inc(&css->refcnt);
+ __css_get(css, 1);
}
static inline bool css_is_removed(struct cgroup_subsys_state *css)
@@ -118,11 +124,11 @@
* css_get() or css_tryget()
*/
-extern void __css_put(struct cgroup_subsys_state *css);
+extern void __css_put(struct cgroup_subsys_state *css, int count);
static inline void css_put(struct cgroup_subsys_state *css)
{
if (!test_bit(CSS_ROOT, &css->flags))
- __css_put(css);
+ __css_put(css, 1);
}
/* bits in struct cgroup flags field */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index be45d2f..cace83d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3746,12 +3746,13 @@
}
}
-void __css_put(struct cgroup_subsys_state *css)
+/* Caller must verify that the css is not for root cgroup */
+void __css_put(struct cgroup_subsys_state *css, int count)
{
struct cgroup *cgrp = css->cgroup;
int val;
rcu_read_lock();
- val = atomic_dec_return(&css->refcnt);
+ val = atomic_sub_return(count, &css->refcnt);
if (val == 1) {
if (notify_on_release(cgrp)) {
set_bit(CGRP_RELEASABLE, &cgrp->flags);