net: add new socket option SO_RESERVE_MEM

This socket option provides a mechanism for users to reserve a certain
amount of memory for the socket to use. When this option is set, kernel
charges the user specified amount of memory to memcg, as well as
sk_forward_alloc. This amount of memory is not reclaimable and is
available in sk_forward_alloc for this socket.
With this socket option set, the networking stack spends less cycles
doing forward alloc and reclaim, which should lead to better system
performance, with the cost of an amount of pre-allocated and
unreclaimable memory, even under memory pressure.

Note:
This socket option is only available when memory cgroup is enabled and we
require this reserved memory to be charged to the user's memcg. We hope
this could avoid mis-behaving users to abused this feature to reserve a
large amount on certain sockets and cause unfairness for others.

Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 69 insertions, 0 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index 512e629f9780..0ecb8590e043 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -947,6 +947,53 @@ void sock_set_mark(struct sock *sk, u32 val)
 }
 EXPORT_SYMBOL(sock_set_mark);
 
+static void sock_release_reserved_memory(struct sock *sk, int bytes)
+{
+	/* Round down bytes to multiple of pages */
+	bytes &= ~(SK_MEM_QUANTUM - 1);
+
+	WARN_ON(bytes > sk->sk_reserved_mem);
+	sk->sk_reserved_mem -= bytes;
+	sk_mem_reclaim(sk);
+}
+
+static int sock_reserve_memory(struct sock *sk, int bytes)
+{
+	long allocated;
+	bool charged;
+	int pages;
+
+	if (!mem_cgroup_sockets_enabled || !sk->sk_memcg)
+		return -EOPNOTSUPP;
+
+	if (!bytes)
+		return 0;
+
+	pages = sk_mem_pages(bytes);
+
+	/* pre-charge to memcg */
+	charged = mem_cgroup_charge_skmem(sk->sk_memcg, pages,
+					  GFP_KERNEL | __GFP_RETRY_MAYFAIL);
+	if (!charged)
+		return -ENOMEM;
+
+	/* pre-charge to forward_alloc */
+	allocated = sk_memory_allocated_add(sk, pages);
+	/* If the system goes into memory pressure with this
+	 * precharge, give up and return error.
+	 */
+	if (allocated > sk_prot_mem_limits(sk, 1)) {
+		sk_memory_allocated_sub(sk, pages);
+		mem_cgroup_uncharge_skmem(sk->sk_memcg, pages);
+		return -ENOMEM;
+	}
+	sk->sk_forward_alloc += pages << SK_MEM_QUANTUM_SHIFT;
+
+	sk->sk_reserved_mem += pages << SK_MEM_QUANTUM_SHIFT;
+
+	return 0;
+}
+
 /*
  *	This is meant for all protocols to use and covers goings on
  *	at the socket level. Everything here is generic.
@@ -1367,6 +1414,23 @@ set_sndbuf:
 					  ~SOCK_BUF_LOCK_MASK);
 		break;
 
+	case SO_RESERVE_MEM:
+	{
+		int delta;
+
+		if (val < 0) {
+			ret = -EINVAL;
+			break;
+		}
+
+		delta = val - sk->sk_reserved_mem;
+		if (delta < 0)
+			sock_release_reserved_memory(sk, -delta);
+		else
+			ret = sock_reserve_memory(sk, delta);
+		break;
+	}
+
 	default:
 		ret = -ENOPROTOOPT;
 		break;
@@ -1733,6 +1797,10 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 		v.val = sk->sk_userlocks & SOCK_BUF_LOCK_MASK;
 		break;
 
+	case SO_RESERVE_MEM:
+		v.val = sk->sk_reserved_mem;
+		break;
+
 	default:
 		/* We implement the SO_SNDLOWAT etc to not be settable
 		 * (1003.1g 7).
@@ -2045,6 +2113,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 	newsk->sk_dst_pending_confirm = 0;
 	newsk->sk_wmem_queued	= 0;
 	newsk->sk_forward_alloc = 0;
+	newsk->sk_reserved_mem  = 0;
 	atomic_set(&newsk->sk_drops, 0);
 	newsk->sk_send_head	= NULL;
 	newsk->sk_userlocks	= sk->sk_userlocks & ~SOCK_BINDPORT_LOCK;