From: Abel Wu <wuyun.abel@bytedance.com>
Date: Mon, 14 Aug 2023 15:09:11 +0800
Subject: net-memcg: Fix scope of sockmem pressure indicators
Git-commit: ac8a52962164a50e693fa021d3564d7745b83a7f
Patch-mainline: v6.6-rc1
References: bsc#1216759

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>
Acked-by: Michal Koutný <mkoutny@suse.com>
---
 include/linux/memcontrol.h |    9 +++++++--
 mm/vmpressure.c            |    8 ++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -228,6 +228,11 @@ struct mem_cgroup {
 	 */
 	struct mem_cgroup_stat_cpu __percpu *stat;
 
+	/*
+	 * Hint of reclaim pressure for socket memroy management. Note
+	 * that this indicator should NOT be used in legacy cgroup mode
+	 * where socket memory is accounted/charged separately.
+	 */
 	unsigned long		socket_pressure;
 
 	/* Legacy tcp memory accounting */
@@ -836,8 +841,8 @@ void mem_cgroup_sk_alloc(struct sock *sk
 void mem_cgroup_sk_free(struct sock *sk);
 static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 {
-	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && memcg->tcpmem_pressure)
-		return true;
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return !!memcg->tcpmem_pressure;
 	do {
 		if (time_before(jiffies, memcg->socket_pressure))
 			return true;
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -232,6 +232,14 @@ void vmpressure(gfp_t gfp, struct mem_cg
 	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);
 
 	/*