net: fix sk_mem_reclaim_partial()

commit 1a24e04e upstream.

sk_mem_reclaim_partial() goal is to ensure each socket has
one SK_MEM_QUANTUM forward allocation. This is needed both for
performance and better handling of memory pressure situations in
follow up patches.

SK_MEM_QUANTUM is currently a page, but might be reduced to 4096 bytes
as some arches have 64KB pages.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
 - Keep using atomic_long_sub() directly, not sk_memory_allocated_sub()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

include/net/sock.h

@@ -961,7 +961,7 @@ static inline struct inode *SOCK_INODE(struct socket *socket)
  * Functions for memory accounting
  */
 extern int __sk_mem_schedule(struct sock *sk, int size, int kind);
-extern void __sk_mem_reclaim(struct sock *sk);
+void __sk_mem_reclaim(struct sock *sk, int amount);
 
 #define SK_MEM_QUANTUM ((int)PAGE_SIZE)
 #define SK_MEM_QUANTUM_SHIFT ilog2(SK_MEM_QUANTUM)
@@ -1000,7 +1000,7 @@ static inline void sk_mem_reclaim(struct sock *sk)
 	if (!sk_has_account(sk))
 		return;
 	if (sk->sk_forward_alloc >= SK_MEM_QUANTUM)
-		__sk_mem_reclaim(sk);
+		__sk_mem_reclaim(sk, sk->sk_forward_alloc);
 }
 
 static inline void sk_mem_reclaim_partial(struct sock *sk)
@@ -1008,7 +1008,7 @@ static inline void sk_mem_reclaim_partial(struct sock *sk)
 	if (!sk_has_account(sk))
 		return;
 	if (sk->sk_forward_alloc > SK_MEM_QUANTUM)
-		__sk_mem_reclaim(sk);
+		__sk_mem_reclaim(sk, sk->sk_forward_alloc - 1);
 }
 
 static inline void sk_mem_charge(struct sock *sk, int size)

net/core/sock.c

@@ -1750,14 +1750,15 @@ EXPORT_SYMBOL(__sk_mem_schedule);
 /**
  *	__sk_reclaim - reclaim memory_allocated
  *	@sk: socket
+ *	@amount: number of bytes (rounded down to a SK_MEM_QUANTUM multiple)
  */
-void __sk_mem_reclaim(struct sock *sk)
+void __sk_mem_reclaim(struct sock *sk, int amount)
 {
 	struct proto *prot = sk->sk_prot;
 
-	atomic_long_sub(sk->sk_forward_alloc >> SK_MEM_QUANTUM_SHIFT,
-		   prot->memory_allocated);
-	sk->sk_forward_alloc &= SK_MEM_QUANTUM - 1;
+	amount >>= SK_MEM_QUANTUM_SHIFT;
+	atomic_long_sub(amount, prot->memory_allocated);
+	sk->sk_forward_alloc -= amount << SK_MEM_QUANTUM_SHIFT;
 
 	if (prot->memory_pressure && *prot->memory_pressure &&
 	    (atomic_long_read(prot->memory_allocated) < prot->sysctl_mem[0]))