/*
 * These routines also need to handle stuff like marking pages dirty
 * and/or accessed for architectures that don't do it in hardware (most
 * RISC architectures).  The early dirtying is also good on the i386.
 *
 * There is also a hook called "update_mmu_cache()" that architectures
 * with external mmu caches can use to update those (ie the Sparc or
 * PowerPC hashed page tables that act as extended TLBs).
 *
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte mapped but not yet locked.
 * We return with pte unmapped and unlocked.
 *
 * The mmap_sem may have been released depending on flags and our
 * return value.  See filemap_fault() and __lock_page_or_retry().
 */
static int handle_pte_fault(struct mm_struct *mm,
		     struct vm_area_struct *vma, unsigned long address,
		     pte_t *pte, pmd_t *pmd, unsigned int flags)
{
	pte_t entry;
	spinlock_t *ptl;

	/*
	 * some architectures can have larger ptes than wordsize,
	 * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and CONFIG_32BIT=y,
	 * so READ_ONCE or ACCESS_ONCE cannot guarantee atomic accesses.
	 * The code below just needs a consistent view for the ifs and
	 * we later double check anyway with the ptl lock held. So here
	 * a barrier will do.
	 */
	entry = *pte;
	barrier();
	if (!pte_present(entry)) {
		if (pte_none(entry)) {
			if (vma->vm_ops)
				return do_fault(mm, vma, address, pte, pmd,
						flags, entry);

			return do_anonymous_page(mm, vma, address, pte, pmd,
					flags);
		}
		return do_swap_page(mm, vma, address,
					pte, pmd, flags, entry);
	}

	if (pte_protnone(entry))
		return do_numa_page(mm, vma, address, entry, pte, pmd);

	ptl = pte_lockptr(mm, pmd);
	spin_lock(ptl);
	if (unlikely(!pte_same(*pte, entry)))
		goto unlock;
	if (flags & FAULT_FLAG_WRITE) {
		if (!pte_write(entry))
			return do_wp_page(mm, vma, address,
					pte, pmd, ptl, entry);
		entry = pte_mkdirty(entry);
	}
	entry = pte_mkyoung(entry);
	if (ptep_set_access_flags(vma, address, pte, entry, flags & FAULT_FLAG_WRITE)) {
		update_mmu_cache(vma, address, pte);
	} else {
		/*
		 * This is needed only for protection faults but the arch code
		 * is not yet telling us if this is a protection fault or not.
		 * This still avoids useless tlb flushes for .text page faults
		 * with threads.
		 */
		if (flags & FAULT_FLAG_WRITE)
			flush_tlb_fix_spurious_fault(vma, address);
	}
unlock:
	pte_unmap_unlock(pte, ptl);
	return 0;
}
 

關於2.4的do_no_page複雜了好多，判斷項也多了不少。。/mm/memory.c

/*
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte mapped but not yet locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
		unsigned long address, pte_t *page_table, pmd_t *pmd,
		unsigned int flags)
{
	struct mem_cgroup *memcg;
	struct page *page;
	spinlock_t *ptl;
	pte_t entry;

	pte_unmap(page_table);

	/* File mapping without ->vm_ops ? */
	if (vma->vm_flags & VM_SHARED)
		return VM_FAULT_SIGBUS;

	/* Check if we need to add a guard page to the stack */
	if (check_stack_guard_page(vma, address) < 0)
		return VM_FAULT_SIGSEGV;

	/* Use the zero-page for reads */
	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm)) {
		entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
						vma->vm_page_prot));
		page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
		if (!pte_none(*page_table))
			goto unlock;
		goto setpte;
	}

	/* Allocate our own private page. */
	if (unlikely(anon_vma_prepare(vma)))
		goto oom;
	page = alloc_zeroed_user_highpage_movable(vma, address);
	if (!page)
		goto oom;

	if (mem_cgroup_try_charge(page, mm, GFP_KERNEL, &memcg))
		goto oom_free_page;

	/*
	 * The memory barrier inside __SetPageUptodate makes sure that
	 * preceeding stores to the page contents become visible before
	 * the set_pte_at() write.
	 */
	__SetPageUptodate(page);

	entry = mk_pte(page, vma->vm_page_prot);
	if (vma->vm_flags & VM_WRITE)
		entry = pte_mkwrite(pte_mkdirty(entry));

	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
	if (!pte_none(*page_table))
		goto release;

	inc_mm_counter_fast(mm, MM_ANONPAGES);
	page_add_new_anon_rmap(page, vma, address);
	mem_cgroup_commit_charge(page, memcg, false);
	lru_cache_add_active_or_unevictable(page, vma);
setpte:
	set_pte_at(mm, address, page_table, entry);

	/* No need to invalidate - it was non-present before */
	update_mmu_cache(vma, address, page_table);
unlock:
	pte_unmap_unlock(page_table, ptl);
	return 0;
release:
	mem_cgroup_cancel_charge(page, memcg);
	page_cache_release(page);
	goto unlock;
oom_free_page:
	page_cache_release(page);
oom:
	return VM_FAULT_OOM;
}
 

/*
 * The in-memory structure used to track swap areas.
 */
struct swap_info_struct {
	unsigned long	flags;		/* SWP_USED etc: see above */
	signed short	prio;		/* swap priority of this type */
	struct plist_node list;		/* entry in swap_active_head */
	struct plist_node avail_list;	/* entry in swap_avail_head */
	signed char	type;		/* strange name for an index */
	unsigned int	max;		/* extent of the swap_map */
	unsigned char *swap_map;	/* vmalloc'ed array of usage counts */
	struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
	struct swap_cluster_info free_cluster_head; /* free cluster list head */
	struct swap_cluster_info free_cluster_tail; /* free cluster list tail */
	unsigned int lowest_bit;	/* index of first free in swap_map */
	unsigned int highest_bit;	/* index of last free in swap_map */
	unsigned int pages;		/* total of usable pages of swap */
	unsigned int inuse_pages;	/* number of those currently in use */
	unsigned int cluster_next;	/* likely index for next allocation */
	unsigned int cluster_nr;	/* countdown to next cluster search */
	struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
	struct swap_extent *curr_swap_extent;
	struct swap_extent first_swap_extent;
	struct block_device *bdev;	/* swap device or bdev of swap file */
	struct file *swap_file;		/* seldom referenced */
	unsigned int old_block_size;	/* seldom referenced */
#ifdef CONFIG_FRONTSWAP
	unsigned long *frontswap_map;	/* frontswap in-use, one bit per page */
	atomic_t frontswap_pages;	/* frontswap pages in-use counter */
#endif
	spinlock_t lock;		/*
					 * protect map scan related fields like
					 * swap_map, lowest_bit, highest_bit,
					 * inuse_pages, cluster_next,
					 * cluster_nr, lowest_alloc,
					 * highest_alloc, free/discard cluster
					 * list. other fields are only changed
					 * at swapon/swapoff, so are protected
					 * by swap_lock. changing flags need
					 * hold this lock and swap_lock. If
					 * both locks need hold, hold swap_lock
					 * first.
					 */
	struct work_struct discard_work; /* discard worker */
	struct swap_cluster_info discard_cluster_head; /* list head of discard clusters */
	struct swap_cluster_info discard_cluster_tail; /* list tail of discard clusters */
};
 

int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
{
	int error;

	error = radix_tree_maybe_preload(gfp_mask);
	if (!error) {
		error = __add_to_swap_cache(page, entry);
		radix_tree_preload_end();
	}
	return error;
}

/*
 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
	int error;
	struct address_space *address_space;

	VM_BUG_ON_PAGE(!PageLocked(page), page);
	VM_BUG_ON_PAGE(PageSwapCache(page), page);
	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);

	page_cache_get(page);
	SetPageSwapCache(page);
	set_page_private(page, entry.val);

	address_space = swap_address_space(entry);
	spin_lock_irq(&address_space->tree_lock);
	error = radix_tree_insert(&address_space->page_tree,
					entry.val, page);
	if (likely(!error)) {
		address_space->nrpages++;
		__inc_zone_page_state(page, NR_FILE_PAGES);
		INC_CACHE_INFO(add_total);
	}
	spin_unlock_irq(&address_space->tree_lock);

	if (unlikely(error)) {
		/*
		 * Only the context which have set SWAP_HAS_CACHE flag
		 * would call add_to_swap_cache().
		 * So add_to_swap_cache() doesn't returns -EEXIST.
		 */
		VM_BUG_ON(error == -EEXIST);
		set_page_private(page, 0UL);
		ClearPageSwapCache(page);
		page_cache_release(page);
	}

	return error;
}