Finish polishing the session memory management:

Also check if the http_max_hdr param changes.

Describe http_max_hdr as per pool.

Add SES_DeletePool() function.

bin/varnishd/cache.h

@@ -849,7 +849,6 @@ unsigned WRW_WriteH(struct worker *w, const txt *hh, const char *suf);
 void WRW_Sendfile(struct worker *w, int fd, off_t off, unsigned len);
 #endif  /* SENDFILE_WORKS */
 
-
 /* cache_session.c [SES] */
 struct sess *SES_New(struct worker *wrk, struct sesspool *pp);
 struct sess *SES_Alloc(void);
@@ -857,7 +856,7 @@ void SES_Close(struct sess *sp, const char *reason);
 void SES_Delete(struct sess *sp, const char *reason);
 void SES_Charge(struct sess *sp);
 struct sesspool *SES_NewPool(void);
-
+void SES_DeletePool(struct sesspool *sp, struct worker *wrk);
 
 /* cache_shmlog.c */
 void VSL_Init(void);

bin/varnishd/cache_session.c

@@ -51,11 +51,14 @@ struct sessmem {
 #define SESSMEM_MAGIC		0x555859c5
 
 	struct sesspool		*pool;
-	struct sess		sess;
+
 	unsigned		workspace;
+	uint16_t		nhttp;
 	void			*wsp;
 	struct http		*http[2];
 	VTAILQ_ENTRY(sessmem)	list;
+
+	struct sess		sess;
 };
 
 struct sesspool {
@@ -120,14 +123,20 @@ ses_sm_alloc(void)
 
 	sm = (void*)p;
 	p += sizeof *sm;
+
 	sm->magic = SESSMEM_MAGIC;
 	sm->workspace = nws;
+	sm->nhttp = nhttp;
+
 	sm->http[0] = HTTP_create(p, nhttp);
 	p += hl;
+
 	sm->http[1] = HTTP_create(p, nhttp);
 	p += hl;
+
 	sm->wsp = p;
 	p += nws;
+
 	assert(p == q);
 
 	return (sm);
@@ -318,6 +327,7 @@ SES_Delete(struct sess *sp, const char *reason)
 	    b->fetch, b->hdrbytes, b->bodybytes);
 
 	if (sm->workspace != params->sess_workspace ||
+	    sm->nhttp != (uint16_t)params->http_max_hdr ||
 	    pp->nsess > params->max_sess) {
 		free(sm);
 		Lck_Lock(&pp->mtx);
@@ -341,7 +351,7 @@ SES_Delete(struct sess *sp, const char *reason)
 }
 
 /*--------------------------------------------------------------------
- * Create a new pool to allocate from
+ * Create and delete pools
  */
 
 struct sesspool *
@@ -355,3 +365,25 @@ SES_NewPool(void)
 	Lck_New(&sp->mtx, lck_sessmem);
 	return (sp);
 }
+
+void
+SES_DeletePool(struct sesspool *sp, struct worker *wrk)
+{
+	struct sessmem *sm;
+
+	CHECK_OBJ_NOTNULL(sp, SESSPOOL_MAGIC);
+	CHECK_OBJ_NOTNULL(wrk, WORKER_MAGIC);
+	Lck_Lock(&sp->mtx);
+	while (!VTAILQ_EMPTY(&sp->freelist)) {
+		sm = VTAILQ_FIRST(&sp->freelist);
+		CHECK_OBJ_NOTNULL(sm, SESSMEM_MAGIC);
+		VTAILQ_REMOVE(&sp->freelist, sm, list);
+		FREE_OBJ(sm);
+		wrk->stats.sessmem_free++;
+		sp->nsess--;
+	}
+	AZ(sp->nsess);
+	Lck_Unlock(&sp->mtx);
+	Lck_Delete(&sp->mtx);
+	FREE_OBJ(sp);
+}

bin/varnishd/mgt_param.c

@@ -777,7 +777,7 @@ static const struct parspec input_parspec[] = {
 		"off", "bool" },
 	{ "session_max", tweak_uint,
 		&master.max_sess, 1000, UINT_MAX,
-		"Maximum number of sessions we will allocate "
+		"Maximum number of sessions we will allocate from one pool "
 		"before just dropping connections.\n"
 		"This is mostly an anti-DoS measure, and setting it plenty "
 		"high should not hurt, as long as you have the memory for "