Implement totalram and freeram computation for sysinfo

kernel/src/syscall/sysinfo.rs

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
 use aster_time::read_monotonic_time;
+use ostd::mm::stat::{mem_total, mem_available};
 
 use super::SyscallReturn;
 use crate::prelude::*;
@@ -8,23 +9,25 @@ use crate::prelude::*;
 #[derive(Debug, Default, Clone, Copy, Pod)]
 #[repr(C)]
 pub struct sysinfo {
-    uptime: i64,
-    loads: [u64; 3],
-    totalram: u64,
-    freeram: u64,
-    sharedram: u64,
-    bufferram: u64,
-    totalswap: u64,
-    freeswap: u64,
-    procs: u16,
-    totalhigh: u64,
-    freehigh: u64,
-    mem_unit: u32,
+    uptime: i64,     /* Seconds since boot */
+    loads: [u64; 3], /* 1, 5, and 15 minute load averages */
+    totalram: u64,   /* Total usable main memory size */
+    freeram: u64,    /* Available memory size */
+    sharedram: u64,  /* Amount of shared memory */
+    bufferram: u64,  /* Memory used by buffers */
+    totalswap: u64,  /* Total swap space size */
+    freeswap: u64,   /* swap space still available */
+    procs: u16,      /* Number of current processes */
+    totalhigh: u64,  /* Total high memory size */
+    freehigh: u64,   /* Available high memory size */
+    mem_unit: u32,   /* Memory unit size in bytes */
 }
 
 pub fn sys_sysinfo(sysinfo_addr: Vaddr, ctx: &Context) -> Result<SyscallReturn> {
     let info = sysinfo {
         uptime: read_monotonic_time().as_secs() as i64,
+        totalram: mem_total() as u64,
+        freeram: mem_available() as u64,
         ..Default::default() // TODO: add other system information
     };
     ctx.user_space().write_val(sysinfo_addr, &info)?;