mm: memcontrol: track move_lock state internally
The complexity of memcg page stat synchronization is currently leaking
into the callsites, forcing them to keep track of the move_lock state and
the IRQ flags. Simplify the API by tracking it in the memcg.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Wu Fengguang <fengguang.wu@intel.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 f3f8a4f..028d07c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -325,9 +325,11 @@
/*
* set > 0 if pages under this cgroup are moving to other cgroup.
*/
- atomic_t moving_account;
+ atomic_t moving_account;
/* taken only while moving_account > 0 */
- spinlock_t move_lock;
+ spinlock_t move_lock;
+ struct task_struct *move_lock_task;
+ unsigned long move_lock_flags;
/*
* percpu counter.
*/
@@ -1977,34 +1979,33 @@
/**
* mem_cgroup_begin_page_stat - begin a page state statistics transaction
* @page: page that is going to change accounted state
- * @locked: &memcg->move_lock slowpath was taken
- * @flags: IRQ-state flags for &memcg->move_lock
*
* This function must mark the beginning of an accounted page state
* change to prevent double accounting when the page is concurrently
* being moved to another memcg:
*
- * memcg = mem_cgroup_begin_page_stat(page, &locked, &flags);
+ * memcg = mem_cgroup_begin_page_stat(page);
* if (TestClearPageState(page))
* mem_cgroup_update_page_stat(memcg, state, -1);
- * mem_cgroup_end_page_stat(memcg, locked, flags);
- *
- * The RCU lock is held throughout the transaction. The fast path can
- * get away without acquiring the memcg->move_lock (@locked is false)
- * because page moving starts with an RCU grace period.
- *
- * The RCU lock also protects the memcg from being freed when the page
- * state that is going to change is the only thing preventing the page
- * from being uncharged. E.g. end-writeback clearing PageWriteback(),
- * which allows migration to go ahead and uncharge the page before the
- * account transaction might be complete.
+ * mem_cgroup_end_page_stat(memcg);
*/
-struct mem_cgroup *mem_cgroup_begin_page_stat(struct page *page,
- bool *locked,
- unsigned long *flags)
+struct mem_cgroup *mem_cgroup_begin_page_stat(struct page *page)
{
struct mem_cgroup *memcg;
+ unsigned long flags;
+ /*
+ * The RCU lock is held throughout the transaction. The fast
+ * path can get away without acquiring the memcg->move_lock
+ * because page moving starts with an RCU grace period.
+ *
+ * The RCU lock also protects the memcg from being freed when
+ * the page state that is going to change is the only thing
+ * preventing the page from being uncharged.
+ * E.g. end-writeback clearing PageWriteback(), which allows
+ * migration to go ahead and uncharge the page before the
+ * account transaction might be complete.
+ */
rcu_read_lock();
if (mem_cgroup_disabled())
@@ -2014,16 +2015,22 @@
if (unlikely(!memcg))
return NULL;
- *locked = false;
if (atomic_read(&memcg->moving_account) <= 0)
return memcg;
- spin_lock_irqsave(&memcg->move_lock, *flags);
+ spin_lock_irqsave(&memcg->move_lock, flags);
if (memcg != page->mem_cgroup) {
- spin_unlock_irqrestore(&memcg->move_lock, *flags);
+ spin_unlock_irqrestore(&memcg->move_lock, flags);
goto again;
}
- *locked = true;
+
+ /*
+ * When charge migration first begins, we can have locked and
+ * unlocked page stat updates happening concurrently. Track
+ * the task who has the lock for mem_cgroup_end_page_stat().
+ */
+ memcg->move_lock_task = current;
+ memcg->move_lock_flags = flags;
return memcg;
}
@@ -2031,14 +2038,17 @@
/**
* mem_cgroup_end_page_stat - finish a page state statistics transaction
* @memcg: the memcg that was accounted against
- * @locked: value received from mem_cgroup_begin_page_stat()
- * @flags: value received from mem_cgroup_begin_page_stat()
*/
-void mem_cgroup_end_page_stat(struct mem_cgroup *memcg, bool *locked,
- unsigned long *flags)
+void mem_cgroup_end_page_stat(struct mem_cgroup *memcg)
{
- if (memcg && *locked)
- spin_unlock_irqrestore(&memcg->move_lock, *flags);
+ if (memcg && memcg->move_lock_task == current) {
+ unsigned long flags = memcg->move_lock_flags;
+
+ memcg->move_lock_task = NULL;
+ memcg->move_lock_flags = 0;
+
+ spin_unlock_irqrestore(&memcg->move_lock, flags);
+ }
rcu_read_unlock();
}