memcg: fix race at move_parent around compound_order()
A fix up mem_cgroup_move_parent() which use compound_order() in
asynchronous manner. This compound_order() may return unknown value
because we don't take lock. Use PageTransHuge() and HPAGE_SIZE instead
of it.
Also clean up for mem_cgroup_move_parent().
- remove unnecessary initialization of local variable.
- rename charge_size -> page_size
- remove unnecessary (wrong) comment.
- added a comment about THP.
Note:
Current design take compound_page_lock() in caller of move_account().
This should be revisited when we implement direct move_task of hugepage
without splitting.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8ab1d42..3878cfe 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2236,7 +2236,12 @@
{
int ret = -EINVAL;
unsigned long flags;
-
+ /*
+ * The page is isolated from LRU. So, collapse function
+ * will not handle this page. But page splitting can happen.
+ * Do this check under compound_page_lock(). The caller should
+ * hold it.
+ */
if ((charge_size > PAGE_SIZE) && !PageTransHuge(pc->page))
return -EBUSY;
@@ -2268,7 +2273,7 @@
struct cgroup *cg = child->css.cgroup;
struct cgroup *pcg = cg->parent;
struct mem_cgroup *parent;
- int charge = PAGE_SIZE;
+ int page_size = PAGE_SIZE;
unsigned long flags;
int ret;
@@ -2281,22 +2286,24 @@
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);
+
+ if (PageTransHuge(page))
+ page_size = HPAGE_SIZE;
parent = mem_cgroup_from_cont(pcg);
- ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, charge);
+ ret = __mem_cgroup_try_charge(NULL, gfp_mask,
+ &parent, false, page_size);
if (ret || !parent)
goto put_back;
- if (charge > PAGE_SIZE)
+ if (page_size > PAGE_SIZE)
flags = compound_lock_irqsave(page);
- ret = mem_cgroup_move_account(pc, child, parent, true, charge);
+ ret = mem_cgroup_move_account(pc, child, parent, true, page_size);
if (ret)
- mem_cgroup_cancel_charge(parent, charge);
+ mem_cgroup_cancel_charge(parent, page_size);
- if (charge > PAGE_SIZE)
+ if (page_size > PAGE_SIZE)
compound_unlock_irqrestore(page, flags);
put_back:
putback_lru_page(page);