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Commit e9e58a4e authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: avoid use cmpxchg in swap cgroup maintainance 



swap_cgroup uses 2bytes data and uses cmpxchg in a new operation.  2byte
cmpxchg/xchg is not available on some archs.  This patch replaces
cmpxchg/xchg with operations under lock.

Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reported-by: Sachin Sant <sachinp@in.ibm.com> wrote:
Acked-by: default avatarBalbir Singh <balbir@in.ibm.com>
Acked-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a3d3203e

mm/page_cgroup.c

+16 −4
Original line number Diff line number Diff line
@@ -284,6 +284,7 @@ static DEFINE_MUTEX(swap_cgroup_mutex); 
struct swap_cgroup_ctrl {

	struct page **map;

	unsigned long length;

	spinlock_t	lock;

};



struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
@@ -353,16 +354,22 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent, 
	struct swap_cgroup_ctrl *ctrl;

	struct page *mappage;

	struct swap_cgroup *sc;

	unsigned long flags;

	unsigned short retval;



	ctrl = &swap_cgroup_ctrl[type];



	mappage = ctrl->map[idx];

	sc = page_address(mappage);

	sc += pos;

	if (cmpxchg(&sc->id, old, new) == old)

		return old;

	spin_lock_irqsave(&ctrl->lock, flags);

	retval = sc->id;

	if (retval == old)

		sc->id = new;

	else

		return 0;

		retval = 0;

	spin_unlock_irqrestore(&ctrl->lock, flags);

	return retval;

}



/**
@@ -383,13 +390,17 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id) 
	struct page *mappage;

	struct swap_cgroup *sc;

	unsigned short old;

	unsigned long flags;



	ctrl = &swap_cgroup_ctrl[type];



	mappage = ctrl->map[idx];

	sc = page_address(mappage);

	sc += pos;

	old = xchg(&sc->id, id);

	spin_lock_irqsave(&ctrl->lock, flags);

	old = sc->id;

	sc->id = id;

	spin_unlock_irqrestore(&ctrl->lock, flags);



	return old;

}
@@ -441,6 +452,7 @@ int swap_cgroup_swapon(int type, unsigned long max_pages) 
	mutex_lock(&swap_cgroup_mutex);

	ctrl->length = length;

	ctrl->map = array;

	spin_lock_init(&ctrl->lock);

	if (swap_cgroup_prepare(type)) {

		/* memory shortage */

		ctrl->map = NULL;