sock: Doc behaviors for pressure heurisitics

[linux-2.6-microblaze.git] / net / core / sock.c

diff --git a/net/core/sock.c b/net/core/sock.c
index 4384252..9f969e3 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3067,7 +3067,14 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
        if (allocated > sk_prot_mem_limits(sk, 2))
                goto suppress_allocation;
 
-       /* guarantee minimum buffer size under pressure */
+       /* Guarantee minimum buffer size under pressure (either global
+        * or memcg) to make sure features described in RFC 7323 (TCP
+        * Extensions for High Performance) work properly.
+        *
+        * This rule does NOT stand when exceeds global or memcg's hard
+        * limit, or else a DoS attack can be taken place by spawning
+        * lots of sockets whose usage are under minimum buffer size.
+        */
        if (kind == SK_MEM_RECV) {
                if (atomic_read(&sk->sk_rmem_alloc) < sk_get_rmem0(sk, prot))
                        return 1;
@@ -3088,6 +3095,11 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
 
                if (!sk_under_memory_pressure(sk))
                        return 1;
+
+               /* Try to be fair among all the sockets under global
+                * pressure by allowing the ones that below average
+                * usage to raise.
+                */
                alloc = sk_sockets_allocated_read_positive(sk);
                if (sk_prot_mem_limits(sk, 2) > alloc *
                    sk_mem_pages(sk->sk_wmem_queued +