memcg: improve performance in moving swap charge
Try to reduce overheads in moving swap charge by:
- Adds a new function(__mem_cgroup_put), which takes "count" as a arg and
decrement mem->refcnt by "count".
- Removed res_counter_uncharge, css_put, and mem_cgroup_put from the path
of moving swap account, and consolidate all of them into mem_cgroup_clear_mc.
We cannot do that about mc.to->refcnt.
These changes reduces the overhead from 1.35sec to 0.9sec to move charges
of 1G anonymous memory(including 500MB swap) in my test environment.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
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 e883198..b00ec74 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -255,6 +255,7 @@
struct mem_cgroup *to;
unsigned long precharge;
unsigned long moved_charge;
+ unsigned long moved_swap;
struct task_struct *moving_task; /* a task moving charges */
wait_queue_head_t waitq; /* a waitq for other context */
} mc = {
@@ -2277,6 +2278,7 @@
* @entry: swap entry to be moved
* @from: mem_cgroup which the entry is moved from
* @to: mem_cgroup which the entry is moved to
+ * @need_fixup: whether we should fixup res_counters and refcounts.
*
* It succeeds only when the swap_cgroup's record for this entry is the same
* as the mem_cgroup's id of @from.
@@ -2287,7 +2289,7 @@
* both res and memsw, and called css_get().
*/
static int mem_cgroup_move_swap_account(swp_entry_t entry,
- struct mem_cgroup *from, struct mem_cgroup *to)
+ struct mem_cgroup *from, struct mem_cgroup *to, bool need_fixup)
{
unsigned short old_id, new_id;
@@ -2295,27 +2297,36 @@
new_id = css_id(&to->css);
if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
- if (!mem_cgroup_is_root(from))
- res_counter_uncharge(&from->memsw, PAGE_SIZE);
mem_cgroup_swap_statistics(from, false);
- mem_cgroup_put(from);
- /*
- * we charged both to->res and to->memsw, so we should uncharge
- * to->res.
- */
- if (!mem_cgroup_is_root(to))
- res_counter_uncharge(&to->res, PAGE_SIZE);
mem_cgroup_swap_statistics(to, true);
+ /*
+ * This function is only called from task migration context now.
+ * It postpones res_counter and refcount handling till the end
+ * of task migration(mem_cgroup_clear_mc()) for performance
+ * improvement. But we cannot postpone mem_cgroup_get(to)
+ * because if the process that has been moved to @to does
+ * swap-in, the refcount of @to might be decreased to 0.
+ */
mem_cgroup_get(to);
- css_put(&to->css);
-
+ if (need_fixup) {
+ if (!mem_cgroup_is_root(from))
+ res_counter_uncharge(&from->memsw, PAGE_SIZE);
+ mem_cgroup_put(from);
+ /*
+ * we charged both to->res and to->memsw, so we should
+ * uncharge to->res.
+ */
+ if (!mem_cgroup_is_root(to))
+ res_counter_uncharge(&to->res, PAGE_SIZE);
+ css_put(&to->css);
+ }
return 0;
}
return -EINVAL;
}
#else
static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
- struct mem_cgroup *from, struct mem_cgroup *to)
+ struct mem_cgroup *from, struct mem_cgroup *to, bool need_fixup)
{
return -EINVAL;
}
@@ -3398,9 +3409,9 @@
atomic_inc(&mem->refcnt);
}
-static void mem_cgroup_put(struct mem_cgroup *mem)
+static void __mem_cgroup_put(struct mem_cgroup *mem, int count)
{
- if (atomic_dec_and_test(&mem->refcnt)) {
+ if (atomic_sub_and_test(count, &mem->refcnt)) {
struct mem_cgroup *parent = parent_mem_cgroup(mem);
__mem_cgroup_free(mem);
if (parent)
@@ -3408,6 +3419,11 @@
}
}
+static void mem_cgroup_put(struct mem_cgroup *mem)
+{
+ __mem_cgroup_put(mem, 1);
+}
+
/*
* Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
*/
@@ -3789,6 +3805,29 @@
__mem_cgroup_cancel_charge(mc.from, mc.moved_charge);
mc.moved_charge = 0;
}
+ /* we must fixup refcnts and charges */
+ if (mc.moved_swap) {
+ WARN_ON_ONCE(mc.moved_swap > INT_MAX);
+ /* uncharge swap account from the old cgroup */
+ if (!mem_cgroup_is_root(mc.from))
+ res_counter_uncharge(&mc.from->memsw,
+ PAGE_SIZE * mc.moved_swap);
+ __mem_cgroup_put(mc.from, mc.moved_swap);
+
+ if (!mem_cgroup_is_root(mc.to)) {
+ /*
+ * we charged both to->res and to->memsw, so we should
+ * uncharge to->res.
+ */
+ res_counter_uncharge(&mc.to->res,
+ PAGE_SIZE * mc.moved_swap);
+ VM_BUG_ON(test_bit(CSS_ROOT, &mc.to->css.flags));
+ __css_put(&mc.to->css, mc.moved_swap);
+ }
+ /* we've already done mem_cgroup_get(mc.to) */
+
+ mc.moved_swap = 0;
+ }
mc.from = NULL;
mc.to = NULL;
mc.moving_task = NULL;
@@ -3818,11 +3857,13 @@
VM_BUG_ON(mc.to);
VM_BUG_ON(mc.precharge);
VM_BUG_ON(mc.moved_charge);
+ VM_BUG_ON(mc.moved_swap);
VM_BUG_ON(mc.moving_task);
mc.from = from;
mc.to = mem;
mc.precharge = 0;
mc.moved_charge = 0;
+ mc.moved_swap = 0;
mc.moving_task = current;
ret = mem_cgroup_precharge_mc(mm);
@@ -3883,8 +3924,12 @@
break;
case MC_TARGET_SWAP:
ent = target.ent;
- if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to))
+ if (!mem_cgroup_move_swap_account(ent,
+ mc.from, mc.to, false)) {
mc.precharge--;
+ /* we fixup refcnts and charges later. */
+ mc.moved_swap++;
+ }
break;
default:
break;