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From: KAMEZAWA Hiroyuki on 14 Mar 2010 21:10
On Sun, 14 Mar 2010 16:18:06 +0530
Sachin Sant <sachinp(a)in.ibm.com> wrote:

> On a PowerPC box, latest 34-rc1 git(d89b218b8...) fails to build
> with CGROUPS_MEM_RES_CTRL_SWAP=y.
>
> LD init/built-in.o
> LD .tmp_vmlinux1
> mm/built-in.o: In function __xchg:
> arch/powerpc/include/asm/system.h:331: undefined reference to .__xchg_called_with_bad_pointer
> mm/built-in.o: In function __cmpxchg:
> arch/powerpc/include/asm/system.h:474: undefined reference to .__cmpxchg_called_with_bad_pointer
> make: *** [.tmp_vmlinux1] Error 1
>
> The code in question was added via commit 024914477e...
>
> memcg: move charges of anonymous swap
>
Oh..ok, powerpc (and other archs?) can't do 2byte cmpxchg and xchg.
Then, we should use spinlock rather than that.

How about this ? Nishimura-san, could you consider something better ?
We need a quick fix.

==
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 <kamezawa.hiroyu(a)jp.fujitsu.com>
---
mm/page_cgroup.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

Index: mmotm-2.6.34-Mar11/mm/page_cgroup.c
===================================================================
--- mmotm-2.6.34-Mar11.orig/mm/page_cgroup.c
+++ mmotm-2.6.34-Mar11/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_e
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_en
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, unsigne
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;

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Prev: mm,migration: Do not try to migrate unmapped anonymous pages
Next: [PATCH] Staging: asus_oled: changes spaces to tabs in asus_oled.c Ran checkpatch.pl as per TODO mentioned that one line had spaces, fixed it. Signed-off-by: M. Willis Monroe <willismonroe@gmail.com>