inetpeer: restore small inet_peer structures

Addition of rcu_head to struct inet_peer added 16bytes on 64bit arches.

Thats a bit unfortunate, since old size was exactly 64 bytes.

This can be solved, using an union between this rcu_head an four fields,
that are normally used only when a refcount is taken on inet_peer.
rcu_head is used only when refcnt=-1, right before structure freeing.

Add a inet_peer_refcheck() function to check this assertion for a while.

We can bring back SLAB_HWCACHE_ALIGN qualifier in kmem cache creation.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 5 deletions

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index 617404730422..417d0c894f29 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -22,11 +22,21 @@ struct inet_peer {
         __u32                   dtime;          /* the time of last use of not
                                                  * referenced entries */
         atomic_t                refcnt;
-        atomic_t                rid;            /* Frag reception counter */
-        atomic_t                ip_id_count;    /* IP ID for the next packet */
-        __u32                   tcp_ts;
-        __u32                   tcp_ts_stamp;
-        struct rcu_head         rcu;
+        /*
+         * Once inet_peer is queued for deletion (refcnt == -1), following fields
+         * are not available: rid, ip_id_count, tcp_ts, tcp_ts_stamp
+         * We can share memory with rcu_head to keep inet_peer small
+         * (less then 64 bytes)
+         */
+        union {
+                struct {
+                        atomic_t        rid;            /* Frag reception counter */
+                        atomic_t        ip_id_count;    /* IP ID for the next packet */
+                        __u32           tcp_ts;
+                        __u32           tcp_ts_stamp;
+                };
+                struct rcu_head         rcu;
+        };
 };
 
 void                    inet_initpeers(void) __init;
@@ -37,10 +47,21 @@ struct inet_peer	*inet_getpeer(__be32 daddr, int create);
 /* can be called from BH context or outside */
 extern void inet_putpeer(struct inet_peer *p);
 
+/*
+ * temporary check to make sure we dont access rid, ip_id_count, tcp_ts,
+ * tcp_ts_stamp if no refcount is taken on inet_peer
+ */
+static inline void inet_peer_refcheck(const struct inet_peer *p)
+{
+        WARN_ON_ONCE(atomic_read(&p->refcnt) <= 0);
+}
+
+
 /* can be called with or without local BH being disabled */
 static inline __u16     inet_getid(struct inet_peer *p, int more)
 {
         more++;
+        inet_peer_refcheck(p);
         return atomic_add_return(more, &p->ip_id_count) - more;
 }