QUIC: avoid excessive buffer allocations in stream output.

Previously, when a few bytes were send to a QUIC stream by the application, a
4K buffer was allocated for these bytes.  Then a STREAM frame was created and
that entire buffer was used as data for that frame.  The frame with the buffer
were in use up until the frame was acked by client.  Meanwhile, when more
bytes were send to the stream, more buffers were allocated and assigned as
data to newer STREAM frames.  In this scenario most buffer memory is unused.

Now the unused part of the stream output buffer is available for further
stream output while earlier parts of the buffer are waiting to be acked.
This is achieved by splitting the output buffer.

1 files changed, 24 insertions, 9 deletions

diff --git a/src/event/quic/ngx_event_quic_streams.c b/src/event/quic/ngx_event_quic_streams.c
index 295aa54aa..d5facc270 100644
--- a/src/event/quic/ngx_event_quic_streams.c
+++ b/src/event/quic/ngx_event_quic_streams.c
@@ -838,8 +838,9 @@ static ngx_chain_t *
 ngx_quic_stream_send_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
 {
     size_t                  n, flow;
+    ngx_buf_t              *b;
     ngx_event_t            *wev;
-    ngx_chain_t            *cl;
+    ngx_chain_t            *out, **ll;
     ngx_connection_t       *pc;
     ngx_quic_frame_t       *frame;
     ngx_quic_stream_t      *qs;
@@ -862,18 +863,30 @@ ngx_quic_stream_send_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
 
     n = (limit && (size_t) limit < flow) ? (size_t) limit : flow;
 
-    frame = ngx_quic_alloc_frame(pc);
-    if (frame == NULL) {
+    if (ngx_quic_order_bufs(pc, &qs->out, in, n, 0) != NGX_OK) {
         return NGX_CHAIN_ERROR;
     }
 
-    frame->data = ngx_quic_copy_chain(pc, in, n);
-    if (frame->data == NGX_CHAIN_ERROR) {
-        return NGX_CHAIN_ERROR;
+    n = 0;
+    out = qs->out;
+
+    for (ll = &out; *ll; ll = &(*ll)->next) {
+        b = (*ll)->buf;
+
+        if (b->sync) {
+            /* hole */
+            break;
+        }
+
+        n += b->last - b->pos;
     }
 
-    for (n = 0, cl = frame->data; cl; cl = cl->next) {
-        n += ngx_buf_size(cl->buf);
+    qs->out = *ll;
+    *ll = NULL;
+
+    frame = ngx_quic_alloc_frame(pc);
+    if (frame == NULL) {
+        return NGX_CHAIN_ERROR;
     }
 
     while (in && ngx_buf_size(in->buf) == 0) {
@@ -882,6 +895,7 @@ ngx_quic_stream_send_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
 
     frame->level = ssl_encryption_application;
     frame->type = NGX_QUIC_FT_STREAM;
+    frame->data = out;
     frame->u.stream.off = 1;
     frame->u.stream.len = 1;
     frame->u.stream.fin = 0;
@@ -977,6 +991,7 @@ ngx_quic_stream_cleanup_handler(void *data)
 
     ngx_rbtree_delete(&qc->streams.tree, &qs->node);
     ngx_quic_free_bufs(pc, qs->in);
+    ngx_quic_free_bufs(pc, qs->out);
 
     if (qc->closing) {
         /* schedule handler call to continue ngx_quic_close_connection() */
@@ -1098,7 +1113,7 @@ ngx_quic_handle_stream_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
         qs->final_size = last;
     }
 
-    if (ngx_quic_order_bufs(c, &qs->in, frame->data,
+    if (ngx_quic_order_bufs(c, &qs->in, frame->data, f->length,
                             f->offset - qs->recv_offset)
         != NGX_OK)
     {