val = __this_cpu_read(memcg->stat->nr_page_events);
next = __this_cpu_read(memcg->stat->targets[target]);
/* from time_after() in jiffies.h */
- if ((long)next - (long)val < 0) {
+ if ((long)(next - val) < 0) {
switch (target) {
case MEM_CGROUP_TARGET_THRESH:
next = val + THRESHOLDS_EVENTS_TARGET;
* @page: the page
*
* This function protects unlocked LRU pages from being moved to
- * another cgroup and stabilizes their page->mem_cgroup binding.
+ * another cgroup.
+ *
+ * It ensures lifetime of the returned memcg. Caller is responsible
+ * for the lifetime of the page; __unlock_page_memcg() is available
+ * when @page might get freed inside the locked section.
*/
-void lock_page_memcg(struct page *page)
+struct mem_cgroup *lock_page_memcg(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 itself from being freed. E.g. writeback
+ * doesn't hold a page reference and relies on PG_writeback to
+ * keep off truncation, migration and so forth.
+ */
rcu_read_lock();
if (mem_cgroup_disabled())
- return;
+ return NULL;
again:
memcg = page->mem_cgroup;
if (unlikely(!memcg))
- return;
+ return NULL;
if (atomic_read(&memcg->moving_account) <= 0)
- return;
+ return memcg;
spin_lock_irqsave(&memcg->move_lock, flags);
if (memcg != page->mem_cgroup) {
memcg->move_lock_task = current;
memcg->move_lock_flags = flags;
- return;
+ return memcg;
}
EXPORT_SYMBOL(lock_page_memcg);
/**
- * unlock_page_memcg - unlock a page->mem_cgroup binding
- * @page: the page
+ * __unlock_page_memcg - unlock and unpin a memcg
+ * @memcg: the memcg
+ *
+ * Unlock and unpin a memcg returned by lock_page_memcg().
*/
-void unlock_page_memcg(struct page *page)
+void __unlock_page_memcg(struct mem_cgroup *memcg)
{
- struct mem_cgroup *memcg = page->mem_cgroup;
-
if (memcg && memcg->move_lock_task == current) {
unsigned long flags = memcg->move_lock_flags;
rcu_read_unlock();
}
+
+/**
+ * unlock_page_memcg - unlock a page->mem_cgroup binding
+ * @page: the page
+ */
+void unlock_page_memcg(struct page *page)
+{
+ __unlock_page_memcg(page->mem_cgroup);
+}
EXPORT_SYMBOL(unlock_page_memcg);
/*
/**
* mem_cgroup_low - check if memory consumption is below the normal range
- * @root: the highest ancestor to consider
+ * @root: the top ancestor of the sub-tree being checked
* @memcg: the memory cgroup to check
*
* Returns %true if memory consumption of @memcg, and that of all
- * configurable ancestors up to @root, is below the normal range.
+ * ancestors up to (but not including) @root, is below the normal range.
+ *
+ * @root is exclusive; it is never low when looked at directly and isn't
+ * checked when traversing the hierarchy.
+ *
+ * Excluding @root enables using memory.low to prioritize memory usage
+ * between cgroups within a subtree of the hierarchy that is limited by
+ * memory.high or memory.max.
+ *
+ * For example, given cgroup A with children B and C:
+ *
+ * A
+ * / \
+ * B C
+ *
+ * and
+ *
+ * 1. A/memory.current > A/memory.high
+ * 2. A/B/memory.current < A/B/memory.low
+ * 3. A/C/memory.current >= A/C/memory.low
+ *
+ * As 'A' is high, i.e. triggers reclaim from 'A', and 'B' is low, we
+ * should reclaim from 'C' until 'A' is no longer high or until we can
+ * no longer reclaim from 'C'. If 'A', i.e. @root, isn't excluded by
+ * mem_cgroup_low when reclaming from 'A', then 'B' won't be considered
+ * low and we will reclaim indiscriminately from both 'B' and 'C'.
*/
bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg)
{
if (mem_cgroup_disabled())
return false;
- /*
- * The toplevel group doesn't have a configurable range, so
- * it's never low when looked at directly, and it is not
- * considered an ancestor when assessing the hierarchy.
- */
-
- if (memcg == root_mem_cgroup)
- return false;
-
- if (page_counter_read(&memcg->memory) >= memcg->low)
+ if (!root)
+ root = root_mem_cgroup;
+ if (memcg == root)
return false;
- while (memcg != root) {
- memcg = parent_mem_cgroup(memcg);
-
- if (memcg == root_mem_cgroup)
- break;
-
+ for (; memcg != root; memcg = parent_mem_cgroup(memcg)) {
if (page_counter_read(&memcg->memory) >= memcg->low)
return false;
}
+
return true;
}