net: keep sk->sk_forward_alloc as small as possible

Currently, tcp_memory_allocated can hit tcp_mem[] limits quite fast.

Each TCP socket can forward allocate up to 2 MB of memory, even after
flow became less active.

10,000 sockets can have reserved 20 GB of memory,
and we have no shrinker in place to reclaim that.

Instead of trying to reclaim the extra allocations in some places,
just keep sk->sk_forward_alloc values as small as possible.

This should not impact performance too much now we have per-cpu
reserves: Changes to tcp_memory_allocated should not be too frequent.

For sockets not using SO_RESERVE_MEM:
 - idle sockets (no packets in tx/rx queues) have zero forward alloc.
 - non idle sockets have a forward alloc smaller than one page.

Note:

 - Removal of SK_RECLAIM_CHUNK and SK_RECLAIM_THRESHOLD
   is left to MPTCP maintainers as a follow up.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 2 insertions, 27 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index cf288f7e9019..0063e8410a4e 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1627,19 +1627,6 @@ static inline void sk_mem_reclaim_final(struct sock *sk)
 	sk_mem_reclaim(sk);
 }
 
-static inline void sk_mem_reclaim_partial(struct sock *sk)
-{
-	int reclaimable;
-
-	if (!sk_has_account(sk))
-		return;
-
-	reclaimable = sk->sk_forward_alloc - sk_unused_reserved_mem(sk);
-
-	if (reclaimable > (int)PAGE_SIZE)
-		__sk_mem_reclaim(sk, reclaimable - 1);
-}
-
 static inline void sk_mem_charge(struct sock *sk, int size)
 {
 	if (!sk_has_account(sk))
@@ -1647,29 +1634,17 @@ static inline void sk_mem_charge(struct sock *sk, int size)
 	sk->sk_forward_alloc -= size;
 }
 
-/* the following macros control memory reclaiming in sk_mem_uncharge()
+/* the following macros control memory reclaiming in mptcp_rmem_uncharge()
  */
 #define SK_RECLAIM_THRESHOLD	(1 << 21)
 #define SK_RECLAIM_CHUNK	(1 << 20)
 
 static inline void sk_mem_uncharge(struct sock *sk, int size)
 {
-	int reclaimable;
-
 	if (!sk_has_account(sk))
 		return;
 	sk->sk_forward_alloc += size;
-	reclaimable = sk->sk_forward_alloc - sk_unused_reserved_mem(sk);
-
-	/* Avoid a possible overflow.
-	 * TCP send queues can make this happen, if sk_mem_reclaim()
-	 * is not called and more than 2 GBytes are released at once.
-	 *
-	 * If we reach 2 MBytes, reclaim 1 MBytes right now, there is
-	 * no need to hold that much forward allocation anyway.
-	 */
-	if (unlikely(reclaimable >= SK_RECLAIM_THRESHOLD))
-		__sk_mem_reclaim(sk, SK_RECLAIM_CHUNK);
+	sk_mem_reclaim(sk);
 }
 
 /*