[Devel] [PATCH RHEL7 COMMIT] ub/mm/writeback: do not check dirty limits for ub0

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.18.2.vz7.14.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.18.2.vz7.14.3
------>
commit f3f20e3d8c6bf8b4bade064073c5b35b3f592960
Author: Vladimir Davydov <vdavydov at virtuozzo.com>
Date:   Tue May 17 20:37:24 2016 +0400

    ub/mm/writeback: do not check dirty limits for ub0
    
    It's just a waste of time, because ub0 has no ub-specific dirty limits.
    balance_dirty_pages handles ub0 case anyway.
    
    Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 mm/page-writeback.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 9940d5f..ba5f93a 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1403,9 +1403,11 @@ static void balance_dirty_pages_ub(struct address_space *mapping,
 	unsigned long pages_written = 0;
 	unsigned long pause = 1;
 	struct user_beancounter *ub = get_io_ub();
-
 	struct backing_dev_info *bdi = mapping->backing_dev_info;
 
+	if (ub == get_ub0())
+		return;
+
 	for (;;) {
 		unsigned long nr_to_write = write_chunk - pages_written;