code:expand - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

2250

2251 /*

2252  * Change the size of the data+stack regions of the process.

2253  * If the size is shrinking, it's easy-- just release the

2254  * extra core. If it's growing, and there is core, just

2255  * allocate it and copy the image, taking care to reset

2256  * registers to account for the fact that the system's

2257  * stack has moved.

2259  * swapped out after adjusting the size requirement--

2260  * when it comes in, enough core will be allocated.

2261  * Because of the ssave and SSWAP flags, control will

2262  * resume after the swap in swtch, which executes the return

2263  * from this stack level.

2264  *

2265  * After the expansion, the caller will take care of copying

2266  * the user's stack towards or away from the data area.

2267  */

2268 expand(newsize)

2269 {

2270     int i, n;

2271     register *p, a1, a2;

2272

2273     p = u.u_procp;

2274     n = p->p_size;

2275     p->p_size = newsize;

2276     a1 = p->p_addr;

2277     if(n >= newsize) {

2278           mfree(coremap, n-newsize, a1+newsize);

2279           return;

2280     }

• 若进程图像所需空间保持不变或者变小,则直接释放原内存中多余的空间,返回

2281     savu(u.u_rsav);

• 保存当前r5,r6至u.u_rsav[2]数组中

2282     a2 = malloc(coremap, newsize);

• 若进程图像所需空间变大,则在内存中分配一块新的空间

2283     if(a2 == NULL) {

2284           savu(u.u_ssav);

2285           xswap(p, 1, n);

2286           p->p_flag =| SSWAP;

2287           swtch();

2288           /* no return */

• 若分配失败,则当前进程无法继续在内存中滞留
  • 保存当前r5,r6至u.u_ssav[2]数组中,因为之后会置SSWAP标志,对于带有SSWAP标志的进程,swtch选中其上台时会从u.u_ssav[2]数组中恢复r5,r6
  • 将进程图像调出至 盘交换区
  • 置SSWAP标志
  • 调用swtch进行进程调度

2289     }

2290     p->p_addr = a2;

2291     for(i=0; i<n; i++)

2292               copyseg(a1+i, a2++);

• 若分配成功
  • 将原进程图像搬至新分配的内存空间

2293     mfree(coremap, n, a1);

2295     sureg();

• 释放原进程图像在内存中的空间
• 为进程加载地址映照表

2296 }

2297 /* -------------------------*/

2298

2299

• 内存管理

• code:main
• code:exec
• code:sbreak
• code:grow
• code:xalloc