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-rw-r--r--mm/memcontrol.c99
1 files changed, 85 insertions, 14 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0e3fdbd809c..dd845d25827 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -90,6 +90,7 @@ enum mem_cgroup_stat_index {
MEM_CGROUP_STAT_PGPGOUT_COUNT, /* # of pages paged out */
MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
MEM_CGROUP_EVENTS, /* incremented at every pagein/pageout */
+ MEM_CGROUP_ON_MOVE, /* someone is moving account between groups */
MEM_CGROUP_STAT_NSTATS,
};
@@ -1051,7 +1052,46 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg)
return swappiness;
}
-/* A routine for testing mem is not under move_account */
+static void mem_cgroup_start_move(struct mem_cgroup *mem)
+{
+ int cpu;
+ /* Because this is for moving account, reuse mc.lock */
+ spin_lock(&mc.lock);
+ for_each_possible_cpu(cpu)
+ per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) += 1;
+ spin_unlock(&mc.lock);
+
+ synchronize_rcu();
+}
+
+static void mem_cgroup_end_move(struct mem_cgroup *mem)
+{
+ int cpu;
+
+ if (!mem)
+ return;
+ spin_lock(&mc.lock);
+ for_each_possible_cpu(cpu)
+ per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) -= 1;
+ spin_unlock(&mc.lock);
+}
+/*
+ * 2 routines for checking "mem" is under move_account() or not.
+ *
+ * mem_cgroup_stealed() - checking a cgroup is mc.from or not. This is used
+ * for avoiding race in accounting. If true,
+ * pc->mem_cgroup may be overwritten.
+ *
+ * mem_cgroup_under_move() - checking a cgroup is mc.from or mc.to or
+ * under hierarchy of moving cgroups. This is for
+ * waiting at hith-memory prressure caused by "move".
+ */
+
+static bool mem_cgroup_stealed(struct mem_cgroup *mem)
+{
+ VM_BUG_ON(!rcu_read_lock_held());
+ return this_cpu_read(mem->stat->count[MEM_CGROUP_ON_MOVE]) > 0;
+}
static bool mem_cgroup_under_move(struct mem_cgroup *mem)
{
@@ -1462,35 +1502,62 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
/*
* Currently used to update mapped file statistics, but the routine can be
* generalized to update other statistics as well.
+ *
+ * Notes: Race condition
+ *
+ * We usually use page_cgroup_lock() for accessing page_cgroup member but
+ * it tends to be costly. But considering some conditions, we doesn't need
+ * to do so _always_.
+ *
+ * Considering "charge", lock_page_cgroup() is not required because all
+ * file-stat operations happen after a page is attached to radix-tree. There
+ * are no race with "charge".
+ *
+ * Considering "uncharge", we know that memcg doesn't clear pc->mem_cgroup
+ * at "uncharge" intentionally. So, we always see valid pc->mem_cgroup even
+ * if there are race with "uncharge". Statistics itself is properly handled
+ * by flags.
+ *
+ * Considering "move", this is an only case we see a race. To make the race
+ * small, we check MEM_CGROUP_ON_MOVE percpu value and detect there are
+ * possibility of race condition. If there is, we take a lock.
*/
void mem_cgroup_update_file_mapped(struct page *page, int val)
{
struct mem_cgroup *mem;
- struct page_cgroup *pc;
+ struct page_cgroup *pc = lookup_page_cgroup(page);
+ bool need_unlock = false;
- pc = lookup_page_cgroup(page);
if (unlikely(!pc))
return;
- lock_page_cgroup(pc);
+ rcu_read_lock();
mem = pc->mem_cgroup;
- if (!mem || !PageCgroupUsed(pc))
- goto done;
-
- /*
- * Preemption is already disabled. We can use __this_cpu_xxx
- */
+ if (unlikely(!mem || !PageCgroupUsed(pc)))
+ goto out;
+ /* pc->mem_cgroup is unstable ? */
+ if (unlikely(mem_cgroup_stealed(mem))) {
+ /* take a lock against to access pc->mem_cgroup */
+ lock_page_cgroup(pc);
+ need_unlock = true;
+ mem = pc->mem_cgroup;
+ if (!mem || !PageCgroupUsed(pc))
+ goto out;
+ }
if (val > 0) {
- __this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
+ this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
SetPageCgroupFileMapped(pc);
} else {
- __this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
+ this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
if (!page_mapped(page)) /* for race between dec->inc counter */
ClearPageCgroupFileMapped(pc);
}
-done:
- unlock_page_cgroup(pc);
+out:
+ if (unlikely(need_unlock))
+ unlock_page_cgroup(pc);
+ rcu_read_unlock();
+ return;
}
/*
@@ -3039,6 +3106,7 @@ move_account:
lru_add_drain_all();
drain_all_stock_sync();
ret = 0;
+ mem_cgroup_start_move(mem);
for_each_node_state(node, N_HIGH_MEMORY) {
for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
enum lru_list l;
@@ -3052,6 +3120,7 @@ move_account:
if (ret)
break;
}
+ mem_cgroup_end_move(mem);
memcg_oom_recover(mem);
/* it seems parent cgroup doesn't have enough mem */
if (ret == -ENOMEM)
@@ -4514,6 +4583,7 @@ static void mem_cgroup_clear_mc(void)
mc.to = NULL;
mc.moving_task = NULL;
spin_unlock(&mc.lock);
+ mem_cgroup_end_move(from);
memcg_oom_recover(from);
memcg_oom_recover(to);
wake_up_all(&mc.waitq);
@@ -4544,6 +4614,7 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
VM_BUG_ON(mc.moved_charge);
VM_BUG_ON(mc.moved_swap);
VM_BUG_ON(mc.moving_task);
+ mem_cgroup_start_move(from);
spin_lock(&mc.lock);
mc.from = from;
mc.to = mem;