From e9e58a4ec3b1086d1ed8c915311aef1ae55454fd Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Mon, 15 Mar 2010 00:34:57 -0400 Subject: [PATCH] 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: KAMEZAWA Hiroyuki Reported-by: Sachin Sant wrote: Acked-by: Balbir Singh Acked-by: Daisuke Nishimura Cc: Li Zefan Cc: Benjamin Herrenschmidt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_cgroup.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c index 3dd88539a0e6..6c0081441a32 100644 --- a/mm/page_cgroup.c +++ b/mm/page_cgroup.c @@ -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; -- 2.20.1