|
ge count (while holding
* page_table_lock, as we have here) to make sure that the page
* cannot be freed. If we unmap that page here, a user write
* access to the virtual address will bring back the page, but
* its raised count will (ironically) be taken to mean it's not
* an exclusive swap page, do_wp_page will replace it by a copy
* page, and the user never get to see the data GUP was holding
* the original page for.
*
* This test is also useful for when swapoff (unuse_process) has
* to drop page lock: its reference to the page stops existing
* ptes from being unmapped, so swapoff can make progress.
*/
if (PageSwapCache(page) &&
page_count(page) != page_mapcount(page) + 2) {
ret = SWAP_FAIL;
goto out_unmap;
}
/* Nuke the page table entry. */
flush_cache_page(vma, address);
pteva l = ptep_clear_flush(vma, address, pte);
/* Move the dirty bit to the physical page now the pte is gone. */
if (pte_dirty(pteva l))
set_page_dirty(page);
if (PageAnon(page)) {
swp_entry_t entry = { .val = page->private };
/*
* Store the swap location in the pte.
* See handle_pte_fault() ...
*/
BUG_ON(!PageSwapCache(page));
swap_duplicate(entry);
if (list_empty(&mm->mmlist)) {
spin_lock(&mmlist_lock);
list_add(&mm->mmlist, &init_mm.mmlist);
spin_unlock(&mmlist_lock);
}
set_pte(pte, swp_entry_to_pte(entry));
BUG_ON(pte_file(*pte));
mm->anon_rss--;
}
mm->rss--;
acct_update_integrals();
page_remove_rmap(page);
page_cache_release(page);
out_unmap:
pte_unmap(pte);
out_unlock:
spin_unlock(&mm->page_table_lock);
out:
return ret;
}
static inline unsigned long
vma_address(struct page *page, struct vm_area_struct *vma)
{
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); /* PAGE_CACHE_SHIFT - PAGE_SHIFT值为0，其实就是把page->index赋给pgoff
* 至于为什么要这样右移一下，我也不清楚
*/
unsigned long address;
address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); /* page->index是页的偏移
* vma->vm_pgoff是内存区域首地址的偏移，都是以页为单位
* 相减后再<<PAGE_SHIFT便得到页在内存区域的中的偏移
* 再+vma->vma_start便得到页在内存区域中的地址
*/
if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { /* 得到的地址应该在vm->vm_start和vm_end之间，否则报错 */
/* page should be within any vma from prio_tree_next */
BUG_ON(!PageAnon(page));
return -EFAULT;
}
return address;
}
#define PGDIR_SHIFT 22 // 在i386机子上线性地址0-11位表PTE，12-21表PMD，22-31位表PGD，即线性地址右移22位的结果为其在全局页目录的偏移
#define PTRS_PER_PGD 1024 // 因PGD共10位，所以其最多可以有2^10=1024个全局描述符项
#define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1)) // 得到线性地址address在全局页目录里面的偏移
#define pgd_offset(mm, address) ((mm)->pgd+pgd_index(address)) // 再加上全局描述符基地址（存储在内存描述符mm_struct中的pdg域）后便得到其在全局描述符中的具体位置
|