[RFC PATCH 2/6] memcg: add target_mem_cgroup, mem_cgroup fields to shrink_control

[Ying Han <yinghan@google.com>]

Add target_mem_cgroup and mem_cgroup to shrink_control. The former one is the
"root" memcg under pressure, and the latter one is the "current" memcg under
pressure.

The target_mem_cgroup is initialized with the scan_control's target_mem_cgroup
under target reclaim and default to NULL for rest of the places including
global reclaim.

Signed-off-by: Ying Han <yinghan@google.com>
---
 include/linux/shrinker.h |   10 ++++++++++
 mm/vmscan.c              |    1 +
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index d7165ce..d3732d0 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -12,6 +12,16 @@ struct shrink_control {
 	unsigned long nr_to_scan;
 
 	int priority;
+	/*
+	 * The memory cgroup that is the primary target of this reclaim. Set to
+	 * NULL during a global reclaim.
+	 */
+	struct mem_cgroup *target_mem_cgroup;
+	/*
+	 * The memory cgroup that is current being scanned in order to reclaim
+	 * from the hierarchy of mem_cgroup.
+	 */
+	struct mem_cgroup *mem_cgroup;
 };
 
 /*
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2c7be04..6ffdff6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2323,6 +2323,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 	};
 	struct shrink_control shrink = {
 		.gfp_mask = sc.gfp_mask,
+		.target_mem_cgroup = sc.target_mem_cgroup,
 	};
 
 	/*
-- 
1.7.7.3

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