* Removed the page state PAGE_STATE_BUSY and instead introduced a vm_page::busy

flag. The obvious advantage is that one can still see what state a page is in
  and even move it between states while being marked busy.
* Removed the vm_page::is_dummy flag. Instead we mark marker pages busy, which
  in all cases has the same effect. Introduced a vm_page_is_dummy() that can
  still check whether a given page is a dummy page.
* vm_page_unreserve_pages(): Before adding to the system reserve make sure
  sUnreservedFreePages is non-negative. Otherwise we'd make nonexisting pages
  available for allocation. steal_pages() still has the same problem and it
  can't be solved that easily.
* map_page(): No longer changes the page state/mark the page unbusy. That's the
  caller's responsibility.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@35331 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vm/VMCache.h

@@ -90,6 +90,7 @@ public:
 			void				NotifyPageEvents(vm_page* page, uint32 events)
 									{ if (fPageEventWaiters != NULL)
 										_NotifyPageEvents(page, events); }
+	inline	void				MarkPageUnbusy(vm_page* page);
 
 			vm_page*			LookupPage(off_t offset);
 			void				InsertPage(vm_page* page, off_t offset);
@@ -291,6 +292,14 @@ VMCache::ReleaseRefAndUnlock(bool consumerLocked)
 }
 
 
+void
+VMCache::MarkPageUnbusy(vm_page* page)
+{
+	page->busy = false;
+	NotifyPageEvents(page, PAGE_EVENT_NOT_BUSY);
+}
+
+
 #ifdef __cplusplus
 extern "C" {
 #endif

headers/private/kernel/vm/vm_page.h

@@ -56,6 +56,7 @@ struct vm_page *vm_page_allocate_page_run_no_base(int state, addr_t count,
 	int priority);
 struct vm_page *vm_page_at_index(int32 index);
 struct vm_page *vm_lookup_page(addr_t pageNumber);
+bool vm_page_is_dummy(struct vm_page *page);
 
 #ifdef __cplusplus
 }

headers/private/kernel/vm/vm_types.h

@@ -106,7 +106,7 @@ public:
 #endif
 
 	uint8					state : 3;
-	bool					is_dummy : 1;
+	bool					busy : 1;
 	bool					busy_writing : 1;
 		// used in VMAnonymousCache::Merge()
 	bool					accessed : 1;
@@ -116,7 +116,6 @@ public:
 	int8					usage_count;
 	uint16					wired_count;
 
-
 	VMCacheRef* CacheRef() const			{ return cache_ref; }
 	void SetCacheRef(VMCacheRef* cacheRef)	{ this->cache_ref = cacheRef; }
 
@@ -128,7 +127,6 @@ public:
 enum {
 	PAGE_STATE_ACTIVE = 0,
 	PAGE_STATE_INACTIVE,
-	PAGE_STATE_BUSY,
 	PAGE_STATE_MODIFIED,
 	PAGE_STATE_FREE,
 	PAGE_STATE_CLEAR,