Add capability to get precise free size for userspace

src/libos/src/fs/procfs/meminfo.rs

@@ -14,7 +14,7 @@ impl MemInfoINode {
 impl ProcINode for MemInfoINode {
     fn generate_data_in_bytes(&self) -> vfs::Result<Vec<u8>> {
         let total_ram = USER_SPACE_VM_MANAGER.get_total_size();
-        let free_ram = current!().vm().get_free_size();
+        let free_ram = USER_SPACE_VM_MANAGER.get_precise_free_size();
         Ok(format!(
             "MemTotal:       {} kB\n\
              MemFree:        {} kB\n\

src/libos/src/misc/sysinfo.rs

@@ -26,7 +26,7 @@ pub fn do_sysinfo() -> Result<sysinfo_t> {
     let info = sysinfo_t {
         uptime: time::up_time::get().unwrap().as_secs() as i64, // Duration can't be negative
         totalram: USER_SPACE_VM_MANAGER.get_total_size() as u64,
-        freeram: current!().vm().get_free_size() as u64,
+        freeram: USER_SPACE_VM_MANAGER.get_precise_free_size() as u64,
         procs: table::get_all_processes().len() as u16,
         mem_unit: 1,
         ..Default::default()

src/libos/src/vm/vm_manager.rs

@@ -46,6 +46,15 @@ impl VMManager {
         self.internal().free_manager.free_size()
     }
 
+    pub fn get_precise_free_size(&self) -> usize {
+        let internal = self.internal();
+        internal.free_manager.free_size()
+            + internal
+                .chunks
+                .iter()
+                .fold(0, |acc, chunks| acc + chunks.free_size())
+    }
+
     pub fn verified_clean_when_exit(&self) -> bool {
         let internal = self.internal();
         internal.chunks.len() == 0 && internal.free_manager.free_size() == self.range.size()