feat: increase kernel heap size

Author: flappyBug

os/src/config.rs

@@ -7,7 +7,7 @@ pub const USER_STACK_SIZE: usize = 4096 * 2;
 /// kernel stack size
 pub const KERNEL_STACK_SIZE: usize = 4096 * 2;
 /// kernel heap size
-pub const KERNEL_HEAP_SIZE: usize = 0x200_0000;
+pub const KERNEL_HEAP_SIZE: usize = 0x400_0000; // 64MB
 
 /// page size : 4KB
 pub const PAGE_SIZE: usize = 0x1000;