net-memcg: Fix scope of sockmem pressure indicators

Now there are two indicators of socket memory pressure sit inside
struct mem_cgroup, socket_pressure and tcpmem_pressure, indicating
memory reclaim pressure in memcg->memory and ->tcpmem respectively.

When in legacy mode (cgroupv1), the socket memory is charged into
->tcpmem which is independent of ->memory, so socket_pressure has
nothing to do with socket's pressure at all. Things could be worse
by taking socket_pressure into consideration in legacy mode, as a
pressure in ->memory can lead to premature reclamation/throttling
in socket.

While for the default mode (cgroupv2), the socket memory is charged
into ->memory, and ->tcpmem/->tcpmem_pressure are simply not used.

So {socket,tcpmem}_pressure are only used in default/legacy mode
respectively for indicating socket memory pressure. This patch fixes
the pieces of code that make mixed use of both.

Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index b52644771cc4..22c6689d9302 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -244,6 +244,14 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 	if (mem_cgroup_disabled())
 		return;
 
+	/*
+	 * The in-kernel users only care about the reclaim efficiency
+	 * for this @memcg rather than the whole subtree, and there
+	 * isn't and won't be any in-kernel user in a legacy cgroup.
+	 */
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !tree)
+		return;
+
 	vmpr = memcg_to_vmpressure(memcg);
 
 	/*