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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>
This commit is contained in:
KAMEZAWA Hiroyuki 2011-01-25 15:07:29 -08:00 committed by Linus Torvalds
parent 3d37c4a919
commit 52dbb90509
1 changed files with 16 additions and 9 deletions
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25
mm/memcontrol.c
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@ -2236,7 +2236,12 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
{
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 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
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 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
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);