feat(mm): add slab usage calculation (#768)

* Add slab free space calculation and add it to freeram of sysinfo

kernel/src/mm/allocator/slab.rs

@@ -1,6 +1,3 @@
-//! 当前slab分配器暂时不使用，等待后续完善后合并主线
-#![allow(dead_code)]
-
 use core::{alloc::Layout, ptr::NonNull, sync::atomic::AtomicBool};
 
 use alloc::boxed::Box;
@@ -74,3 +71,11 @@ pub unsafe fn slab_init() {
 pub fn slab_init_state() -> bool {
     unsafe { *SLABINITSTATE.get_mut() }
 }
+
+pub unsafe fn slab_usage() -> SlabUsage {
+    if let Some(ref mut slab) = SLABALLOCATOR {
+        slab.zone.usage()
+    } else {
+        SlabUsage::new(0, 0)
+    }
+}

kernel/src/syscall/misc.rs

@@ -1,7 +1,7 @@
 use crate::{
     arch::{mm::LockedFrameAllocator, rand::rand},
     libs::rand::GRandFlags,
-    mm::allocator::page_frame::FrameAllocator,
+    mm::allocator::{page_frame::FrameAllocator, slab::slab_usage},
 };
 use alloc::vec::Vec;
 use core::cmp;
@@ -38,10 +38,11 @@ impl Syscall {
         let mut sysinfo = SysInfo::default();
 
         let mem = unsafe { LockedFrameAllocator.usage() };
+        let slab_usage = unsafe { slab_usage() };
         sysinfo.uptime = 0;
         sysinfo.loads = [0; 3];
         sysinfo.totalram = mem.total().bytes() as u64;
-        sysinfo.freeram = mem.free().bytes() as u64;
+        sysinfo.freeram = mem.free().bytes() as u64 + slab_usage.free();
         sysinfo.sharedram = 0;
         sysinfo.bufferram = 0;
         sysinfo.totalswap = 0;