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Commit d7b9fff7 authored by Daisuke Nishimura's avatar Daisuke Nishimura Committed by Linus Torvalds
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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: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: default avatarPaul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: default avatarKAMEZAWA 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2468c723

include/linux/cgroup.h

+9 −3
Original line number Diff line number Diff line
@@ -76,6 +76,12 @@ enum { 
	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 @@ static inline void css_get(struct cgroup_subsys_state *css) 
{

	/* 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 @@ static inline bool css_tryget(struct cgroup_subsys_state *css) 
 * 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 */

kernel/cgroup.c

+3 −2
Original line number Diff line number Diff line
@@ -3746,12 +3746,13 @@ static void check_for_release(struct cgroup *cgrp) 
	}

}



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);