4.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Weiner <[email protected]>

commit 4550c4e157ca3da929593bb6c64080a59141af35 upstream.

Cgroup2 currently doesn't have a per-cgroup swappiness setting.  We
might want to add one later - that's a different discussion - but until
we do, the cgroups should always follow the system setting.  Otherwise
it will be unchangeably set to whatever the ancestor inherited from the
system setting at the time of cgroup creation.

Signed-off-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 2b83359c19ca..0a4cd4703f40 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -533,6 +533,10 @@ static inline swp_entry_t get_swap_page(void)
 #ifdef CONFIG_MEMCG
 static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 {
+       /* Cgroup2 doesn't have per-cgroup swappiness */
+       if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+               return vm_swappiness;
+
        /* root ? */
        if (mem_cgroup_disabled() || !memcg->css.parent)
                return vm_swappiness;


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