linux源代码阅读笔记 free_page_tables()分析

/*
77 * This function frees a continuos block of page tables, as needed
78 * by 'exit()'. As does copy_page_tables(), this handles only 4Mb blocks.
79 */
int free_page_tables(unsigned long from,unsigned long size)//size以B为单位而不是以页表为单位
{
unsigned long *pg_table;
unsigned long * dir, nr; if (from & 0x3fffff)
panic("free_page_tables called with wrong alignment");
if (!from)
panic("Trying to free up swapper memory space");
size = (size + 0x3fffff) >> ;//这里计算size大小的内存占用了多少页表。
dir = (unsigned long *) ((from>>) & 0xffc); /* _pg_dir = 0 */
for ( ; size--> ; dir++) {
if (!( & *dir))
continue;
pg_table = (unsigned long *) (0xfffff000 & *dir);
for (nr= ; nr< ; nr++) {
if ( & *pg_table)
free_page(0xfffff000 & *pg_table);
*pg_table = ;
pg_table++;
}
free_page(0xfffff000 & *dir);
*dir = ;
}
invalidate();
return ;
}