linux-kernel - [PATCH net-next v2] net-memcg: Fix scope of sockmem pressure indicators

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Message-Id: <20230814070923.35769-1-wuyun.abel@bytedance.com>
Date:   Mon, 14 Aug 2023 15:09:11 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Ahern <dsahern@...nel.org>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Yu Zhao <yuzhao@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Yafang Shao <laoar.shao@...il.com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Breno Leitao <leitao@...ian.org>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        David Howells <dhowells@...hat.com>,
        Jason Xing <kernelxing@...cent.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Cc:     Abel Wu <wuyun.abel@...edance.com>, Michal Hocko <mhocko@...e.com>,
        linux-kernel@...r.kernel.org (open list),
        netdev@...r.kernel.org (open list:NETWORKING [GENERAL]),
        cgroups@...r.kernel.org (open list:CONTROL GROUP - MEMORY RESOURCE
        CONTROLLER (MEMCG)),
        linux-mm@...ck.org (open list:CONTROL GROUP - MEMORY RESOURCE
        CONTROLLER (MEMCG))
Subject: [PATCH net-next v2] 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@...edance.com>
---
v2:
 - Add a comment to clarify the scope of indicators (Roman)
 - Drop code cleanup on tcpmem_pressure (Roman)
 - Fix the lack of a Fixes: tag (Eric)
---
 include/linux/memcontrol.h | 9 +++++++--
 mm/vmpressure.c            | 8 ++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 5818af8eca5a..dbf26bc89dd4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -284,6 +284,11 @@ struct mem_cgroup {
 	atomic_long_t		memory_events[MEMCG_NR_MEMORY_EVENTS];
 	atomic_long_t		memory_events_local[MEMCG_NR_MEMORY_EVENTS];
 
+	/*
+	 * 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 */
@@ -1727,8 +1732,8 @@ 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, READ_ONCE(memcg->socket_pressure)))
 			return true;
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);
 
 	/*
-- 
2.37.3