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>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 5818af8..dbf26bc 100644 (file)
--- 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 b526447..22c6689 100644 (file)
--- 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);
 
        /*