memcg: do not replicate get_mem_cgroup_from_mm in __mem_cgroup_try_charge
__mem_cgroup_try_charge duplicates get_mem_cgroup_from_mm for charges
which came without a memcg. The only reason seems to be a tiny
optimization when css_tryget is not called if the charge can be consumed
from the stock. Nevertheless css_tryget is very cheap since it has been
reworked to use per-cpu counting so this optimization doesn't give us
anything these days.
So let's drop the code duplication so that the code is more readable.
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
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 87c3ec3..7480022 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2697,52 +2697,14 @@
again:
if (*ptr) { /* css should be a valid one */
memcg = *ptr;
- if (mem_cgroup_is_root(memcg))
- goto done;
- if (consume_stock(memcg, nr_pages))
- goto done;
css_get(&memcg->css);
} else {
- struct task_struct *p;
-
- rcu_read_lock();
- p = rcu_dereference(mm->owner);
- /*
- * Because we don't have task_lock(), "p" can exit.
- * In that case, "memcg" can point to root or p can be NULL with
- * race with swapoff. Then, we have small risk of mis-accouning.
- * But such kind of mis-account by race always happens because
- * we don't have cgroup_mutex(). It's overkill and we allo that
- * small race, here.
- * (*) swapoff at el will charge against mm-struct not against
- * task-struct. So, mm->owner can be NULL.
- */
- memcg = mem_cgroup_from_task(p);
- if (!memcg)
- memcg = root_mem_cgroup;
- if (mem_cgroup_is_root(memcg)) {
- rcu_read_unlock();
- goto done;
- }
- if (consume_stock(memcg, nr_pages)) {
- /*
- * It seems dagerous to access memcg without css_get().
- * But considering how consume_stok works, it's not
- * necessary. If consume_stock success, some charges
- * from this memcg are cached on this cpu. So, we
- * don't need to call css_get()/css_tryget() before
- * calling consume_stock().
- */
- rcu_read_unlock();
- goto done;
- }
- /* after here, we may be blocked. we need to get refcnt */
- if (!css_tryget(&memcg->css)) {
- rcu_read_unlock();
- goto again;
- }
- rcu_read_unlock();
+ memcg = get_mem_cgroup_from_mm(mm);
}
+ if (mem_cgroup_is_root(memcg))
+ goto done;
+ if (consume_stock(memcg, nr_pages))
+ goto done;
do {
bool invoke_oom = oom && !nr_oom_retries;
@@ -2778,8 +2740,8 @@
if (batch > nr_pages)
refill_stock(memcg, batch - nr_pages);
- css_put(&memcg->css);
done:
+ css_put(&memcg->css);
*ptr = memcg;
return 0;
nomem:
