[patch 02/12] mm: memcontrol: rearrange charging fast path

Johannes Weiner
2014-06-16T19:54:22Z

The charging path currently starts out with OOM condition checks when
OOM is the rarest possible case.

Rearrange this code to run OOM/task dying checks only after trying the
percpu charge and the res_counter charge and bail out before entering
reclaim. Attempting a charge does not hurt an (oom-)killed task as
much as every charge attempt having to check OOM conditions. Also,
only check __GFP_NOFAIL when the charge would actually fail.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
---
mm/memcontrol.c | 33 +++++++++++++++++----------------
1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 94531df14d37..e946f7439b16 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2575,22 +2575,6 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,

if (mem_cgroup_is_root(memcg))
goto done;
- /*
- * Unlike in global OOM situations, memcg is not in a physical
- * memory shortage. Allow dying and OOM-killed tasks to
- * bypass the last charges so that they can exit quickly and
- * free their memory.
- */
- if (unlikely(test_thread_flag(TIF_MEMDIE) ||
- fatal_signal_pending(current) ||
- current->flags & PF_EXITING))
- goto bypass;
-
- if (unlikely(task_in_memcg_oom(current)))
- goto nomem;
-
- if (gfp_mask & __GFP_NOFAIL)
- oom = false;
retry:
if (consume_stock(memcg, nr_pages))
goto done;
@@ -2612,6 +2596,20 @@ retry:
goto retry;
}

+ /*
+ * Unlike in global OOM situations, memcg is not in a physical
+ * memory shortage. Allow dying and OOM-killed tasks to
+ * bypass the last charges so that they can exit quickly and
+ * free their memory.
+ */
+ if (unlikely(test_thread_flag(TIF_MEMDIE) ||
+ fatal_signal_pending(current) ||
+ current->flags & PF_EXITING))
+ goto bypass;
+
+ if (unlikely(task_in_memcg_oom(current)))
+ goto nomem;
+
if (!(gfp_mask & __GFP_WAIT))
goto nomem;

@@ -2640,6 +2638,9 @@ retry:
if (mem_cgroup_wait_acct_move(mem_over_limit))
goto retry;

+ if (gfp_mask & __GFP_NOFAIL)
+ goto bypass;
+
if (fatal_signal_pending(current))
goto bypass;

--
2.0.0