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Subject[PATCH 4/4] memcg: fix rmdir, force_empty with THP

Now, when THP is enabled, memcg's rmdir() function is broken
because move_account() for THP page is not supported.

This will cause account leak or -EBUSY issue at rmdir().
This patch fixes the issue by supporting move_account() THP pages.

Changelog:
- style fix.
- add compound_lock for avoiding races.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 37 ++++++++++++++++++++++++++-----------
1 file changed, 26 insertions(+), 11 deletions(-)
Index: mmotm-0107/mm/memcontrol.c
===================================================================
--- mmotm-0107.orig/mm/memcontrol.c
+++ mmotm-0107/mm/memcontrol.c
@@ -2197,8 +2197,11 @@ void mem_cgroup_split_huge_fixup(struct
*/

static void __mem_cgroup_move_account(struct page_cgroup *pc,
- struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
+ struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge,
+ int charge_size)
{
+ int nr_pages = charge_size >> PAGE_SHIFT;
+
VM_BUG_ON(from == to);
VM_BUG_ON(PageLRU(pc->page));
VM_BUG_ON(!page_is_cgroup_locked(pc));
@@ -2212,14 +2215,14 @@ static void __mem_cgroup_move_account(st
__this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
preempt_enable();
}
- mem_cgroup_charge_statistics(from, PageCgroupCache(pc), -1);
+ mem_cgroup_charge_statistics(from, PageCgroupCache(pc), -nr_pages);
if (uncharge)
/* This is not "cancel", but cancel_charge does all we need. */
- mem_cgroup_cancel_charge(from, PAGE_SIZE);
+ mem_cgroup_cancel_charge(from, charge_size);

/* caller should have done css_get */
pc->mem_cgroup = to;
- mem_cgroup_charge_statistics(to, PageCgroupCache(pc), 1);
+ mem_cgroup_charge_statistics(to, PageCgroupCache(pc), nr_pages);
/*
* We charges against "to" which may not have any tasks. Then, "to"
* can be under rmdir(). But in current implementation, caller of
@@ -2234,15 +2237,19 @@ static void __mem_cgroup_move_account(st
* __mem_cgroup_move_account()
*/
static int mem_cgroup_move_account(struct page_cgroup *pc,
- struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
+ 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;
+
lock_page_cgroup(pc);
if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
move_lock_page_cgroup(pc, &flags);
- __mem_cgroup_move_account(pc, from, to, uncharge);
+ __mem_cgroup_move_account(pc, from, to, uncharge, charge_size);
move_unlock_page_cgroup(pc, &flags);
ret = 0;
}
@@ -2267,6 +2274,8 @@ 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;
+ unsigned long flags;
int ret;

/* Is ROOT ? */
@@ -2278,17 +2287,23 @@ 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);

parent = mem_cgroup_from_cont(pcg);
- ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false,
- PAGE_SIZE);
+ ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, charge);
if (ret || !parent)
goto put_back;

- ret = mem_cgroup_move_account(pc, child, parent, true);
+ if (charge > PAGE_SIZE)
+ flags = compound_lock_irqsave(page);
+
+ ret = mem_cgroup_move_account(pc, child, parent, true, charge);
if (ret)
- mem_cgroup_cancel_charge(parent, PAGE_SIZE);
+ mem_cgroup_cancel_charge(parent, charge);
put_back:
+ if (charge > PAGE_SIZE)
+ compound_unlock_irqrestore(page, flags);
putback_lru_page(page);
put:
put_page(page);
@@ -4868,7 +4883,7 @@ retry:
goto put;
pc = lookup_page_cgroup(page);
if (!mem_cgroup_move_account(pc,
- mc.from, mc.to, false)) {
+ mc.from, mc.to, false, PAGE_SIZE)) {
mc.precharge--;
/* we uncharge from mc.from later. */
mc.moved_charge++;


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