if (unlikely(anon_vma_prepare(vma))) {//创建一个anon_vma实例给vma
ret = VM_FAULT_OOM;
goto out;
}
page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,//分配一个页
vma, address);
if (!page) {
ret = VM_FAULT_OOM;
goto out;
}
if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
ret = VM_FAULT_OOM;
page_cache_release(page);
goto out;
}
charged = 1;
/*
* Don't let another task, with possibly unlocked vma,
* keep the mlocked page.
*/
if (vma->vm_flags & VM_LOCKED)
clear_page_mlock(vmf.page);
/*创建数据的副本，将数据拷贝到新分配的页*/
copy_user_highpage(page, vmf.page, address, vma);
__SetPageUptodate(page);
} else {
/*
* If the page will be shareable, see if the backing
* address space wants to know that the page is about
* to become writable
*/
if (vma->vm_ops->page_mkwrite) {
int tmp;
unlock_page(page);
vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
if (unlikely(tmp &
(VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
ret = tmp;
goto unwritable_page;
}
if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
lock_page(page);
if (!page->mapping) {
ret = 0; /* retry the fault */
unlock_page(page);
goto unwritable_page;
}
} else
VM_BUG_ON(!PageLocked(page));
page_mkwrite = 1;
}
}
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
/*
* This silly early PAGE_DIRTY setting removes a race
* due to the bad i386 page protection. But it's valid
* for other architectures too.
*
* Note that if FAULT_FLAG_WRITE is set, we either now have
* an exclusive copy of the page, or this is a shared mapping,
* so we can make it writable and dirty to avoid having to
* handle that later.
*/
/* Only go through if we didn't race with anybody else... */
if (likely(pte_same(*page_table, orig_pte))) {//确定没有竞争，也就是页表项中的内容和之前是一样的
flush_icache_page(vma, page);
entry = mk_pte(page, vma->vm_page_prot);//页表项指向对应的物理页
/*如果是写操作，则将页的访问权限置为RW*/
if (flags & FAULT_FLAG_WRITE)
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
/*如果之前生成的页是匿名的，则将其集成到逆向映射当中*/
if (anon) {
inc_mm_counter(mm, anon_rss);
page_add_new_anon_rmap(page, vma, address);//建立匿名页与第一个vma的逆向映射
} else {
inc_mm_counter(mm, file_rss);
page_add_file_rmap(page);//建立页与vma的普通映射
if (flags & FAULT_FLAG_WRITE) {
dirty_page = page;
get_page(dirty_page);
}
}
set_pte_at(mm, address, page_table, entry);//修改page_table使其指向entry对应的页框
/* no need to invalidate: a not-present page won't be cached */
update_mmu_cache(vma, address, entry);
} else {
if (charged)
mem_cgroup_uncharge_page(page);
if (anon)
page_cache_release(page);
else
anon = 1; /* no anon but release faulted_page */
}
pte_unmap_unlock(page_table, ptl);
out:
if (dirty_page) {
struct address_space *mapping = page->mapping;
if (set_page_dirty(dirty_page))
page_mkwrit