Add workspace_prealloc().

src/misc.h

 #define OC_F_FINAL (OC_F_PRIVATE | OC_F_HFM | OC_F_HFP)
 
 void req_fini(struct req **, struct worker *);
+
+#define VFAIL(ctx, fmt, ...)					\
+	VRT_fail((ctx), "vdp pesi failure: " fmt, __VA_ARGS__)

src/node.c

@@ -50,6 +50,8 @@
 
 #include "misc.h"
 
+#include "vcc_if.h"
+
 #define GZIP_TAILBUF_SZ 13
 
 /* ============================================================
@@ -125,9 +127,9 @@ static void fini_data(struct req *, struct node *);
  */
 
 // known minimum workspace left over for other vmods running during delivery
-static size_t   ws_min_room  = 4 * 1024;
+static volatile size_t   ws_min_room  = 4 * 1024;
 // sensible maximum number of nodes to pre-allocate on the workspace
-static unsigned ws_max_nodes = 32;
+static volatile unsigned ws_max_nodes = 32;
 
 /* ============================================================
  * node/tree alloc / fini / free
@@ -187,6 +189,20 @@ node_size()
 	return (sizeof(struct node));
 }
 
+VCL_VOID
+vmod_workspace_prealloc(VRT_CTX, VCL_BYTES min_free, VCL_INT max_nodes)
+{
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+
+	if (max_nodes < 0) {
+		VFAIL(ctx, "max_nodes (%jd) < 0 in workspace_prealloc()",
+		      max_nodes);
+		return;
+	}
+	ws_min_room = min_free;
+	ws_max_nodes = max_nodes;
+}
+
 struct node *
 node_alloc(struct pesi *pesi)
 {

src/tests/prealloc.vtc

+varnishtest "workspace_prealloc()"
+
+varnish v1 -vcl {
+	import ${vmod_pesi};
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_recv {
+		if (req.url == "/1") {
+			pesi.workspace_prealloc(min_free=10k, max_nodes=64);
+		}
+		elsif (req.url == "/2") {
+			pesi.workspace_prealloc(2k, 16);
+		}
+		elsif (req.url == "/3") {
+			pesi.workspace_prealloc(8k);
+		}
+		elsif (req.url == "/4") {
+			pesi.workspace_prealloc(max_nodes=42);
+		}
+		elsif (req.url == "/5") {
+			pesi.workspace_prealloc(max_nodes=32, min_free=4k);
+		}
+		return (synth(200));
+	}
+} -start
+
+client c1 {
+	txreq -url "/1"
+	rxresp
+	expect resp.status == 200
+	txreq -url "/2"
+	rxresp
+	expect resp.status == 200
+	txreq -url "/3"
+	rxresp
+	expect resp.status == 200
+	txreq -url "/4"
+	rxresp
+	expect resp.status == 200
+	txreq -url "/5"
+	rxresp
+	expect resp.status == 200
+} -run
+
+server s1 {
+	rxreq
+	txresp -body {<esi:include src="/include"/>}
+} -start
+
+server s2 {
+	rxreq
+	txresp -body "foo"
+} -start
+
+varnish v1 -vcl+backend {
+	import ${vmod_pesi};
+
+	sub vcl_init {
+		pesi.workspace_prealloc(max_nodes=0);
+	}
+
+	sub vcl_backend_response {
+		set beresp.do_esi = true;
+	}
+
+	sub vcl_backend_fetch {
+		if (bereq.url == "/") {
+			set bereq.backend = s1;
+		}
+		else {
+			set bereq.backend = s2;
+		}
+	}
+
+	sub vcl_deliver {
+		pesi.activate();
+	}
+}
+
+client c1 {
+	loop 10 {
+		txreq
+		rxresp
+		expect resp.status == 200
+		expect resp.body == "foo"
+	}
+} -run
+
+varnish v1 -vsc MEMPOOL.pesi.*
+varnish v1 -expect MEMPOOL.pesi.pool >= 10
+varnish v1 -expect MEMPOOL.pesi.allocs >= 0
+
+varnish v1 -errvcl "vdp pesi failure: max_nodes (-1) < 0 in workspace_prealloc()" {
+	import ${vmod_pesi};
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		pesi.workspace_prealloc(max_nodes = -1);
+	}
+}

src/vdp_pesi.vcc

@@ -146,6 +146,13 @@ error.
   In short, keeping ``thread`` at the default ``true`` should be the
   right option, the alternative exists just in case.
 
+$Function VOID workspace_prealloc(BYTES min_free=4096, INT max_nodes=32)
+
+Configure workspace pre-allocation of objects in variable-sized
+internal data structures.
+
+XXX ...
+
 $Function STRING version()
 
 Return the version string for this VDP.

src/vmod_pesi.c

@@ -36,15 +36,13 @@
 #include "vcc_if.h"
 #include "VSC_pesi.h"
 
+#include "misc.h"
 #include "node_mempool.h"
 #include "pesi_flags.h"
 #include "vdp_pesi.h"
 
 #include "cache/cache_filter.h"
 
-#define VFAIL(ctx, fmt, ...)					\
-	VRT_fail((ctx), "vdp pesi failure: " fmt, __VA_ARGS__)
-
 /* in pesi.c */
 extern struct lock stats_lock;
 extern struct VSC_pesi *stats;
@@ -131,7 +129,11 @@ mpl_fini(struct mempool **mplp)
 
 /* ------------------------------------------------------------
  * VMOD interface
+ *
+ * vmod_workspace_prealloc() defined in node.c, so as to access
+ * static variables.
  */
+
 VCL_VOID
 vmod_pool(VRT_CTX, VCL_INT min, VCL_INT max, VCL_DURATION max_age)
 {
@@ -344,8 +346,6 @@ vmod_set(VRT_CTX, struct VARGS(set) *args)
 	priv_task->priv = (void *)(uintptr_t)vclflags;
 }
 
-/* Functions */
-
 VCL_STRING
 vmod_version(VRT_CTX)
 {