On Mon, 24 Jan 2011 11:14:02 +0100
Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> On Fri, Jan 21, 2011 at 03:37:26PM +0900, KAMEZAWA Hiroyuki wrote:
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> >
> > A fix for 987eba66e0e6aa654d60881a14731a353ee0acb4
> >
> > A clean up for mem_cgroup_move_parent().
> > - remove unnecessary initialization of local variable.
> > - rename charge_size -> page_size
> > - remove unnecessary (wrong) comment.
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > ---
> > mm/memcontrol.c | 17 +++++++++--------
> > 1 file changed, 9 insertions(+), 8 deletions(-)
> >
> > Index: mmotm-0107/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-0107.orig/mm/memcontrol.c
> > +++ mmotm-0107/mm/memcontrol.c
> > @@ -2265,7 +2265,7 @@ static int mem_cgroup_move_parent(struct
> > struct cgroup *cg = child->css.cgroup;
> > struct cgroup *pcg = cg->parent;
> > struct mem_cgroup *parent;
> > - int charge = PAGE_SIZE;
> > + int page_size;
> > unsigned long flags;
> > int ret;
> >
> > @@ -2278,22 +2278,23 @@ static int mem_cgroup_move_parent(struct
> > goto out;
> > if (isolate_lru_page(page))
> > goto put;
> > - /* The page is isolated from LRU and we have no race with splitting */
> > - charge = PAGE_SIZE << compound_order(page);
> > +
> > + page_size = PAGE_SIZE << compound_order(page);
>
> Okay, so you remove the wrong comment, but that does not make the code
> right. What protects compound_order from reading garbage because the
> page is currently splitting?
>
==
static int mem_cgroup_move_account(struct page_cgroup *pc,
struct mem_cgroup *from, struct mem_cgroup *to,
bool uncharge, int charge_size)
{
int ret = -EINVAL;
unsigned long flags;
if ((charge_size > PAGE_SIZE) && !PageTransHuge(pc->page))
return -EBUSY;
==
This is called under compound_lock(). Then, if someone breaks THP,
-EBUSY and retry.
Thanks,
-Kame
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