[Devel] [PATCH RHEL7 COMMIT] ms/mm: memcontrol: rearrange charging fast path

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.vz7.27.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.vz7.27.10
------>
commit db82eb1d7aecd69f67548bcd52ad89c23f07c575
Author: Johannes Weiner <hannes at cmpxchg.org>
Date:   Mon Jan 16 20:27:08 2017 +0400

    ms/mm: memcontrol: rearrange charging fast path
    
    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 at cmpxchg.org>
    Acked-by: Michal Hocko <mhocko at suse.cz>
    Cc: Hugh Dickins <hughd at google.com>
    Cc: Tejun Heo <tj at kernel.org>
    Cc: Vladimir Davydov <vdavydov at parallels.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-51558
    (cherry picked from commit 06b078fc065fe1fe7097675c8ee416aa2ef94fb3)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/memcontrol.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f904257..f006cdd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2767,21 +2767,6 @@ 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)))
-		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;
@@ -2802,6 +2787,20 @@ 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;
 
@@ -2830,6 +2829,9 @@ 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;