[Devel] [PATCH vz10 13/32] mm/memcg: keep mem_cgroup_per_node::nid available with CONFIG_MEMCG_V1=n

[Konstantin Khorenko]

mem_cgroup_per_node::nid was added into a kABI hole in the middle of the
CONFIG_MEMCG_V1 part of the structure, but it is not a cgroup-v1 field:
percpu_stats_memcg() reads it on the lruvec stats path, to find the
matching per-node structure of the parent an update is forwarded to once a
dying memcg has had its percpu stats freed.  So
CONFIG_MEMCG=y together with CONFIG_MEMCG_V1=n does not build:

  mm/memcontrol.c: error: 'struct mem_cgroup_per_node' has no member
                   named 'nid'

Declare the field in the CONFIG_MEMCG_V1=n branch as well, next to the
other read-mostly members.  The v1 branch is left exactly as it is, so
the layout of the shipped kernel - and with it the kABI checksum - does
not change.

Fixes: be640870964f ("mm/memcg: Free percpu stats memory of dying memcg's")
Feature: fix rh/mm
https://virtuozzo.atlassian.net/browse/VSTOR-134732
Reported-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 include/linux/memcontrol.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 72b6b986a08b..d47c3de71a49 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -109,6 +109,11 @@ struct mem_cgroup_per_node {
 	bool			on_tree;
 	RH_KABI_FILL_HOLE(unsigned short nid)
 #else
+	/*
+	 * Not a v1 field: percpu_stats_memcg() needs the node id to find
+	 * the matching per-node structure of the parent memcg.
+	 */
+	unsigned short		nid;
 	CACHELINE_PADDING(_pad1_);
 #endif
 
-- 
2.47.1