net: tcp_memcontrol: sanitize tcp memory accounting callbacks

There won't be a tcp control soft limit, so integrating the memcg code
into the global skmem limiting scheme complicates things unnecessarily.
Replace this with simple and clear charge and uncharge calls--hidden
behind a jump label--to account skb memory.

Note that this is not purely aesthetic: as a result of shoehorning the
per-memcg code into the same memory accounting functions that handle the
global level, the old code would compare the per-memcg consumption
against the smaller of the per-memcg limit and the global limit.  This
allowed the total consumption of multiple sockets to exceed the global
limit, as long as the individual sockets stayed within bounds.  After
this change, the code will always compare the per-memcg consumption to
the per-memcg limit, and the global consumption to the global limit, and
thus close this loophole.

Without a soft limit, the per-memcg memory pressure state in sockets is
generally questionable.  However, we did it until now, so we continue to
enter it when the hard limit is hit, and packets are dropped, to let
other sockets in the cgroup know that they shouldn't grow their transmit
windows, either.  However, keep it simple in the new callback model and
leave memory pressure lazily when the next packet is accepted (as
opposed to doing it synchroneously when packets are processed).  When
packets are dropped, network performance will already be in the toilet,
so that should be a reasonable trade-off.

As described above, consumption is now checked on the per-memcg level
and the global level separately.  Likewise, memory pressure states are
maintained on both the per-memcg level and the global level, and a
socket is considered under pressure when either level asserts as much.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d9344da..f5de783 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -338,6 +338,38 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
 }
 EXPORT_SYMBOL(tcp_proto_cgroup);
 
+/**
+ * mem_cgroup_charge_skmem - charge socket memory
+ * @proto: proto to charge
+ * @nr_pages: number of pages to charge
+ *
+ * Charges @nr_pages to @proto. Returns %true if the charge fit within
+ * @proto's configured limit, %false if the charge had to be forced.
+ */
+bool mem_cgroup_charge_skmem(struct cg_proto *proto, unsigned int nr_pages)
+{
+	struct page_counter *counter;
+
+	if (page_counter_try_charge(&proto->memory_allocated,
+				    nr_pages, &counter)) {
+		proto->memory_pressure = 0;
+		return true;
+	}
+	page_counter_charge(&proto->memory_allocated, nr_pages);
+	proto->memory_pressure = 1;
+	return false;
+}
+
+/**
+ * mem_cgroup_uncharge_skmem - uncharge socket memory
+ * @proto - proto to uncharge
+ * @nr_pages - number of pages to uncharge
+ */
+void mem_cgroup_uncharge_skmem(struct cg_proto *proto, unsigned int nr_pages)
+{
+	page_counter_uncharge(&proto->memory_allocated, nr_pages);
+}
+
 #endif
 
 #ifdef CONFIG_MEMCG_KMEM