Change the initially allocated VM stack size for each actor

Currently, the VM will allocate a new stack of 262144 bytes (256kb). This makes actors very expensive in terms of memory usage. The default stack allocation size should be lowered, since the stack sizes for actors will generally be much lower than seen in a typical PHP application.

I have a patch for this, but it causes heap corruption issues for some reason:

diff --git a/src/classes/actor.c b/src/classes/actor.c
index 4a410c5257..4b2ccb70a4 100644
--- a/src/classes/actor.c
+++ b/src/classes/actor.c
@@ -311,7 +311,16 @@ zend_object* phactor_actor_ctor(zend_class_entry *entry)

     ph_mcontext_init(&actor_internal->context.mc, process_message_handler);

-    zend_vm_stack_init();
+    zend_vm_stack page = (zend_vm_stack)emalloc(PH_VM_STACK_SIZE);
+    page->top = ZEND_VM_STACK_ELEMENTS(page);
+    page->end = (zval*)((char*)page + PH_VM_STACK_SIZE);
+    page->prev = NULL;
+
+    EG(vm_stack) = page;
+    EG(vm_stack)->top++;
+    EG(vm_stack_top) = EG(vm_stack)->top;
+    EG(vm_stack_end) = EG(vm_stack)->end;
+
     ph_vmcontext_get(&actor_internal->context.vmc);

     /*
diff --git a/src/ph_context.h b/src/ph_context.h
index d494c577da..249b269d45 100644
--- a/src/ph_context.h
+++ b/src/ph_context.h
@@ -53,6 +53,8 @@ typedef struct _ph_context_t {
     ph_vmcontext_t vmc;
 } ph_context_t;

+#define PH_VM_STACK_SIZE 256 // starting size of PHP's VM stack
+
 #ifdef PH_FIXED_STACK_SIZE
 # define STACK_ALIGNMENT 16 // Ensure 16 byte stack alignment (for OS X)

Strangely enough, 256 bytes causes a few test failures (such as the actor-cleanup-on-shutdown.phpt test) with a heap corruption issue, and 512 bytes causes the context-switching-basics3.phpt test to fail with a segfault. Using 64, 128, 1024, 2048, etc, bytes seems to work fine. This needs some investigation before it gets changed.

tpunt / phactor

Change the initially allocated VM stack size for each actor #10