diff --git a/Makefile b/Makefile
index 8bc60d9..034219f 100644
--- a/Makefile
+++ b/Makefile
@@ -195,6 +195,7 @@ UPROGS=\
 	$U/_find\
 	$U/_xargs\
 	$U/_trace\
+	$U/_sysinfotest\
 
 
 
diff --git a/kernel/defs.h b/kernel/defs.h
index f3f5fef..2c07dbe 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -63,6 +63,7 @@ void ramdiskrw(struct buf *);
 void *kalloc(void);
 void kfree(void *);
 void kinit(void);
+int freemem(void);
 
 // log.c
 void initlog(int, struct superblock *);
@@ -106,6 +107,7 @@ void yield(void);
 int either_copyout(int user_dst, uint64 dst, void *src, uint64 len);
 int either_copyin(void *dst, int user_src, uint64 src, uint64 len);
 void procdump(void);
+int proc_size(void);
 
 // swtch.S
 void swtch(struct context *, struct context *);
diff --git a/kernel/kalloc.c b/kernel/kalloc.c
index 0699e7e..8509864 100644
--- a/kernel/kalloc.c
+++ b/kernel/kalloc.c
@@ -7,6 +7,7 @@
 #include "memlayout.h"
 #include "spinlock.h"
 #include "riscv.h"
+#include "proc.h"
 #include "defs.h"
 
 void freerange(void *pa_start, void *pa_end);
@@ -80,3 +81,17 @@ kalloc(void)
     memset((char*)r, 5, PGSIZE); // fill with junk
   return (void*)r;
 }
+
+int 
+freemem(void)
+{
+  struct run* p = kmem.freelist;
+  uint64 num = 0;
+  while (p) {
+    num += 1;
+    p = p->next;
+  }
+  return num * PGSIZE;
+}
+
+
diff --git a/kernel/proc.c b/kernel/proc.c
index db97edc..863b57d 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -691,3 +691,13 @@ procdump(void)
     printf("\n");
   }
 }
+
+int
+proc_size()
+{
+  int i =0, n = 0;
+  for (; i < NPROC; ++i) {
+    if (proc[i].state != UNUSED) n += 1;
+  }
+  return n;
+}
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 9d267af..ad511e1 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -8,9 +8,9 @@
 #include "defs.h"
 
 // 保留系统调用别名
-char* syscalls_name[24] = {"", "fork", "exit", "wait", "pipe", "read", "kill", "exec",
+char* syscalls_name[25] = {"", "fork", "exit", "wait", "pipe", "read", "kill", "exec",
                       "fstat", "chdir", "dup", "getpid", "sbrk", "sleep", "uptime",
-                      "open", "write", "mknod", "unlink", "link", "mkdir", "close", "trace"};
+                      "open", "write", "mknod", "unlink", "link", "mkdir", "close", "trace", "sysinfo"};
 
 // Fetch the uint64 at addr from the current process.
 int
@@ -107,6 +107,7 @@ extern uint64 sys_link(void);
 extern uint64 sys_mkdir(void);
 extern uint64 sys_close(void);
 extern uint64 sys_trace(void);
+extern uint64 sys_sysinfo(void);
 
 // An array mapping syscall numbers from syscall.h
 // to the function that handles the system call.
@@ -133,6 +134,7 @@ static uint64 (*syscalls[])(void) = {
 [SYS_mkdir]   sys_mkdir,
 [SYS_close]   sys_close,
 [SYS_trace]   sys_trace,
+[SYS_sysinfo]   sys_sysinfo,
 };
 
 void
diff --git a/kernel/syscall.h b/kernel/syscall.h
index cc112b9..0dfedc7 100644
--- a/kernel/syscall.h
+++ b/kernel/syscall.h
@@ -21,3 +21,4 @@
 #define SYS_mkdir  20
 #define SYS_close  21
 #define SYS_trace  22
+#define SYS_sysinfo 23
diff --git a/kernel/sysinfo.h b/kernel/sysinfo.h
new file mode 100644
index 0000000..670db98
--- /dev/null
+++ b/kernel/sysinfo.h
@@ -0,0 +1,6 @@
+#include "kernel/types.h"
+struct sysinfo {
+  uint64 freemem;
+  uint64 nproc;
+  uint64 unused_proc_num;
+};
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index 46af86b..ddad0ea 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -5,6 +5,7 @@
 #include "memlayout.h"
 #include "spinlock.h"
 #include "proc.h"
+#include "sysinfo.h"
 
 uint64
 sys_exit(void)
@@ -101,3 +102,19 @@ sys_trace(void)
   myproc()->tracemask = n;
   return 0;
 }
+
+uint64
+sys_sysinfo(void)
+{
+  struct sysinfo info;
+  uint64 addr;
+  argaddr(0, &addr);
+  if (addr < 0) return -1;
+  struct proc* p = myproc();
+  info.nproc = proc_size();
+  info.freemem = freemem();
+  info.unused_proc_num = NPROC - info.nproc;
+  if (copyout(p->pagetable, addr, (char*)&info, sizeof(info)) < 0)
+    return -1;
+  return 0;
+}
diff --git a/user/sysinfotest.c b/user/sysinfotest.c
new file mode 100644
index 0000000..c6d6f6f
--- /dev/null
+++ b/user/sysinfotest.c
@@ -0,0 +1,164 @@
+#include "kernel/types.h"
+#include "kernel/riscv.h"
+/*#include "kernel/sysinfo.h"*/
+#include "user/user.h"
+
+
+void
+sinfo(struct sysinfo *info) {
+  if (sysinfo(info) < 0) {
+    printf("FAIL: sysinfo failed");
+    exit(1);
+  }
+}
+
+//
+// use sbrk() to count how many free physical memory pages there are.
+//
+int
+countfree()
+{
+  uint64 sz0 = (uint64)sbrk(0);
+  struct sysinfo info;
+  int n = 0;
+
+  while(1){
+    if((uint64)sbrk(PGSIZE) == 0xffffffffffffffff){
+      break;
+    }
+    n += PGSIZE;
+  }
+  sinfo(&info);
+  if (info.freemem != 0) {
+    printf("FAIL: there is no free mem, but sysinfo.freemem=%d\n",
+      info.freemem);
+    exit(1);
+  }
+  sbrk(-((uint64)sbrk(0) - sz0));
+  return n;
+}
+
+void
+testmem() {
+  struct sysinfo info;
+  uint64 n = countfree();
+  
+  sinfo(&info);
+
+  if (info.freemem!= n) {
+    printf("FAIL: free mem %d (bytes) instead of %d\n", info.freemem, n);
+    exit(1);
+  }
+  
+  if((uint64)sbrk(PGSIZE) == 0xffffffffffffffff){
+    printf("sbrk failed");
+    exit(1);
+  }
+
+  sinfo(&info);
+    
+  if (info.freemem != n-PGSIZE) {
+    printf("FAIL: free mem %d (bytes) instead of %d\n", n-PGSIZE, info.freemem);
+    exit(1);
+  }
+  
+  if((uint64)sbrk(-PGSIZE) == 0xffffffffffffffff){
+    printf("sbrk failed");
+    exit(1);
+  }
+
+  sinfo(&info);
+    
+  if (info.freemem != n) {
+    printf("FAIL: free mem %d (bytes) instead of %d\n", n, info.freemem);
+    exit(1);
+  }
+}
+
+void
+testcall() {
+  struct sysinfo info;
+  
+  if (sysinfo(&info) < 0) {
+    printf("FAIL: sysinfo failed\n");
+    exit(1);
+  }
+
+  if (sysinfo((struct sysinfo *) 0xeaeb0b5b00002f5e) !=  0xffffffffffffffff) {
+    printf("FAIL: sysinfo succeeded with bad argument\n");
+    exit(1);
+  }
+}
+
+void testproc() {
+  struct sysinfo info;
+  uint64 nproc, unused_proc_num;
+  int status;
+  int pid;
+  
+  sinfo(&info);
+  nproc = info.nproc;
+  unused_proc_num = info.unused_proc_num;
+
+  pid = fork();
+  if(pid < 0){
+    printf("sysinfotest: fork failed\n");
+    exit(1);
+  }
+  if(pid == 0){
+    sinfo(&info);
+    if(info.nproc != nproc+1) {
+      printf("sysinfotest: FAIL nproc is %d instead of %d\n", info.nproc, nproc+1);
+      exit(1);
+    }
+  
+    if(info.unused_proc_num != unused_proc_num-1) {
+      printf("sysinfotest: FAIL unused_proc_num is %d instead of %d\n", info.unused_proc_num, unused_proc_num-1);
+      exit(1);
+    }
+    exit(0);
+  }
+  wait(&status);
+  sinfo(&info);
+  if(info.nproc != nproc) {
+      printf("sysinfotest: FAIL nproc is %d instead of %d\n", info.nproc, nproc);
+      exit(1);
+  }
+  if(info.unused_proc_num != unused_proc_num) {
+      printf("sysinfotest: FAIL unused_proc_num is %d instead of %d\n", info.unused_proc_num, unused_proc_num);
+      exit(1);
+  }
+}
+
+void testbad() {
+  int pid = fork();
+  int xstatus;
+  
+  if(pid < 0){
+    printf("sysinfotest: fork failed\n");
+    exit(1);
+  }
+  if(pid == 0){
+      sinfo(0x0);
+      exit(0);
+  }
+  wait(&xstatus);
+  if(xstatus == -1)  // kernel killed child?
+    exit(0);
+  else {
+    printf("sysinfotest: testbad succeeded %d\n", xstatus);
+    exit(xstatus);
+  }
+}
+
+int
+main(int argc, char *argv[])
+{
+  printf("sysinfotest: start\n");
+  testcall();
+  testmem();
+  testproc();
+  printf("sysinfotest: OK\n");
+  exit(0);
+}
+
diff --git a/user/user.h b/user/user.h
index 36603a0..2af28d8 100644
--- a/user/user.h
+++ b/user/user.h
@@ -1,4 +1,5 @@
 #include "kernel/types.h"
+#include "kernel/sysinfo.h"
 struct stat;
 
 // system calls
@@ -24,6 +25,7 @@ char *sbrk(int);
 int sleep(int);
 int uptime(void);
 int trace(int);
+int sysinfo(struct sysinfo*);
 
 // ulib.c
 int stat(const char *, struct stat *);
diff --git a/user/usys.pl b/user/usys.pl
index 9c97b05..bc109fd 100755
--- a/user/usys.pl
+++ b/user/usys.pl
@@ -37,3 +37,4 @@ entry("sbrk");
 entry("sleep");
 entry("uptime");
 entry("trace");
+entry("sysinfo");