MINOR: quic: implement datagram cleanup for quic_receiver_buf

Each time data is read on QUIC receiver socket, we try to reuse the
first datagram of the currently used quic_receiver_buf instead of
allocating a new one. This algorithm is suboptimal if there is several
unused datagrams as only the first one is tested and its buffer removed
from quic_receiver_buf.

If QUIC traffic is quite substential, this can lead to an important
number of quic_dgram occurences allocated from pool_head_quic_dgram and
a lack of free space in allocated quic_receiver_buf buffers.

To improve this, each time we want to reuse a datagram, we pop elements
until a non-yet released datagram is found or the list is empty. All
intermediary elements are freed and the last found datagram can be
reused. This operation has been extracted in a dedicated function named
quic_rxbuf_purge_dgrams().

This should improve memory consumption incured by quic_dgram instances under heavy
QUIC traffic. Note that there is still room for improvement as if the
first datagram is still in use, it may block several unused datagram
after him. However this requires to support removal of datagrams out of
order which is currently not possible.

This should be backported up to 2.6.

diff --git a/src/quic_sock.c b/src/quic_sock.c
index 652cba83f1dce5b6cf633241465d2b41e1410530..0bb6673175fb4ef048f2b42d737124fe1453c500 100644 (file)
--- a/src/quic_sock.c
+++ b/src/quic_sock.c
@@ -283,6 +283,38 @@ static int quic_lstnr_dgram_dispatch(unsigned char *buf, size_t len, void *owner
        return 0;
 }
 
+/* This function is responsible to remove unused datagram attached in front of
+ * <buf>. Each instances will be freed until a not yet consumed datagram is
+ * found or end of the list is hit. The last unused datagram found is not freed
+ * and is instead returned so that the caller can reuse it if needed.
+ *
+ * Returns the last unused datagram or NULL if no occurence found.
+ */
+static struct quic_dgram *quic_rxbuf_purge_dgrams(struct quic_receiver_buf *buf)
+{
+       struct quic_dgram *cur, *prev = NULL;
+
+       while (!LIST_ISEMPTY(&buf->dgram_list)) {
+               cur = LIST_ELEM(buf->dgram_list.n, struct quic_dgram *, recv_list);
+
+               /* Loop until a not yet consumed datagram is found. */
+               if (cur->buf)
+                       break;
+
+               /* Clear buffer of current unused datagram. */
+               LIST_DELETE(&cur->recv_list);
+               b_del(&buf->buf, cur->len);
+
+               /* Free last found unused datagram. */
+               if (prev)
+                       pool_free(pool_head_quic_dgram, prev);
+               prev = cur;
+       }
+
+       /* Return last unused datagram found. */
+       return prev;
+}
+
 /* Receive data from datagram socket <fd>. Data are placed in <out> buffer of
  * length <len>.
  *
@@ -426,16 +458,7 @@ void quic_sock_fd_iocb(int fd)
         * least one datagram to pick, except the first time we enter
         * this function for this <rxbuf> buffer.
         */
-       if (!LIST_ISEMPTY(&rxbuf->dgrams)) {
-               struct quic_dgram *dg =
-                       LIST_ELEM(rxbuf->dgrams.n, struct quic_dgram *, list);
-
-               if (!dg->buf) {
-                       LIST_DELETE(&dg->list);
-                       b_del(buf, dg->len);
-                       new_dgram = dg;
-               }
-       }
+       new_dgram = quic_rxbuf_purge_dgrams(rxbuf);
 
        params = &l->bind_conf->quic_params;
        max_sz = params->max_udp_payload_size;