xiaoxiang781216 commented on code in PR #7525:
URL: https://github.com/apache/nuttx/pull/7525#discussion_r1038916855
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net/tcp/tcp_conn.c:
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@@ -836,10 +863,25 @@ void tcp_free(FAR struct tcp_conn_s *conn)
}
#endif
- /* Mark the connection available and put it into the free list */
+ /* Mark the connection available. */
conn->tcpstateflags = TCP_CLOSED;
- dq_addlast(&conn->sconn.node, &g_free_tcp_connections);
+
+ /* Check if this is a preallocated connection to store it in the free
+ * connections list, else deallocate it.
+ */
+
+#ifdef CONFIG_NET_ALLOC_CONNS
+ if ((conn->flags & TCP_PREALLOC) == 0)
+ {
+ kmm_free(conn);
Review Comment:
> OK, we agree. (Especially on point 3!)
>
> The only issue is that this way preallocated connections will be always in
BSS. This means that changing this value will have the effect of _moving_ the
connection struct from BSS to heap (as it will be allocated if it is
nevertheless needed).
>
> This may be a bit problematic in arch'es with multiple memory regions.
>
> It is not my favorite, but I can live with that.
>
We can allocate the preallocated conn from heap too, it is no much
difference whether they come from .bss or heap. The more important thing is
never return them to heap.
> One thing that I don't truly like is the `alloc_conn` variable as it is
used now (tcp_conn.c, line 628). I wanted to mark the connection as
pre-allocated within `tcp_initialize()`, but the conn struct will be memset to
0 in line 735, so this information is lost.
>
> Do you have any suggestions for this?
One simple approach is:
1. Don't preallocate conn in startup instead
2. Put conn to free list if free list is smaller than NET_TCP_PREALLOC_CONNS
3. Call kmm_free if the free list is larger than NET_TCP_PREALLOC_CONNS
So, we don't need flag to distinguish whether conn is preallocate or not.
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