steal_pages(): Recheck sUnreservedFreePages after incrementing sPageDeficit.

Since the former is no longer guarded by any lock, there's a race condition
with vm_page_unreserve_pages() which would cause us to wait longer than
necessary.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34898 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/vm/vm_page.cpp

@@ -1470,8 +1470,14 @@ steal_pages(vm_page **pages, size_t count)
 
 		// we need to wait for pages to become inactive
 
-		ConditionVariableEntry freeConditionEntry;
 		sPageDeficit++;
+		if (sUnreservedFreePages >= 0) {
+			// There are enough pages available now. No need to wait after all.
+			sPageDeficit--;
+			return stolen;
+		}
+
+		ConditionVariableEntry freeConditionEntry;
 		freeConditionEntry.Add(&sFreePageQueue);
 		locker.Unlock();