On Mon, 15 Mar 2010 10:02:02 +0900
KAMEZAWA Hiroyuki <kamezawa.hir...@jp.fujitsu.com> wrote:
> On Sun, 14 Mar 2010 16:18:06 +0530
> Sachin Sant <sach...@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.
>
Thank you for fixing this issue.
I think it increases the size of swap_cgroup_ctrl a bit,
but I think it's a good 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.hir...@jp.fujitsu.com>
Acked-by: Daisuke Nishimura <nishim...@mxp.nes.nec.co.jp>
Thanks,
Daisuke Nishimura.
> ---
> 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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