1 files changed, 855 insertions, 0 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
new file mode 100644
index 000000000..3febffe0f
--- /dev/null
+++ b/mm/swap_state.c
@@ -0,0 +1,855 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/mm/swap_state.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *  Swap reorganised 29.12.95, Stephen Tweedie
+ *
+ *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
+ */
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/init.h>
+#include <linux/pagemap.h>
+#include <linux/backing-dev.h>
+#include <linux/blkdev.h>
+#include <linux/pagevec.h>
+#include <linux/migrate.h>
+#include <linux/vmalloc.h>
+#include <linux/swap_slots.h>
+#include <linux/huge_mm.h>
+
+#include <asm/pgtable.h>
+#include "internal.h"
+
+/*
+ * swapper_space is a fiction, retained to simplify the path through
+ * vmscan's shrink_page_list.
+ */
+static const struct address_space_operations swap_aops = {
+	.writepage	= swap_writepage,
+	.set_page_dirty	= swap_set_page_dirty,
+#ifdef CONFIG_MIGRATION
+	.migratepage	= migrate_page,
+#endif
+};
+
+struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
+static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
+static bool enable_vma_readahead __read_mostly = true;
+
+#define SWAP_RA_WIN_SHIFT	(PAGE_SHIFT / 2)
+#define SWAP_RA_HITS_MASK	((1UL << SWAP_RA_WIN_SHIFT) - 1)
+#define SWAP_RA_HITS_MAX	SWAP_RA_HITS_MASK
+#define SWAP_RA_WIN_MASK	(~PAGE_MASK & ~SWAP_RA_HITS_MASK)
+
+#define SWAP_RA_HITS(v)		((v) & SWAP_RA_HITS_MASK)
+#define SWAP_RA_WIN(v)		(((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
+#define SWAP_RA_ADDR(v)		((v) & PAGE_MASK)
+
+#define SWAP_RA_VAL(addr, win, hits)				\
+	(((addr) & PAGE_MASK) |					\
+	 (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |	\
+	 ((hits) & SWAP_RA_HITS_MASK))
+
+/* Initial readahead hits is 4 to start up with a small window */
+#define GET_SWAP_RA_VAL(vma)					\
+	(atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
+
+#define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
+#define ADD_CACHE_INFO(x, nr)	do { swap_cache_info.x += (nr); } while (0)
+
+static struct {
+	unsigned long add_total;
+	unsigned long del_total;
+	unsigned long find_success;
+	unsigned long find_total;
+} swap_cache_info;
+
+unsigned long total_swapcache_pages(void)
+{
+	unsigned int i, j, nr;
+	unsigned long ret = 0;
+	struct address_space *spaces;
+
+	rcu_read_lock();
+	for (i = 0; i < MAX_SWAPFILES; i++) {
+		/*
+		 * The corresponding entries in nr_swapper_spaces and
+		 * swapper_spaces will be reused only after at least
+		 * one grace period.  So it is impossible for them
+		 * belongs to different usage.
+		 */
+		nr = nr_swapper_spaces[i];
+		spaces = rcu_dereference(swapper_spaces[i]);
+		if (!nr || !spaces)
+			continue;
+		for (j = 0; j < nr; j++)
+			ret += spaces[j].nrpages;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
+
+void show_swap_cache_info(void)
+{
+	printk("%lu pages in swap cache\n", total_swapcache_pages());
+	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
+		swap_cache_info.add_total, swap_cache_info.del_total,
+		swap_cache_info.find_success, swap_cache_info.find_total);
+	printk("Free swap  = %ldkB\n",
+		get_nr_swap_pages() << (PAGE_SHIFT - 10));
+	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
+}
+
+/*
+ * __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, i, nr = hpage_nr_pages(page);
+	struct address_space *address_space;
+	pgoff_t idx = swp_offset(entry);
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(PageSwapCache(page), page);
+	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
+
+	page_ref_add(page, nr);
+	SetPageSwapCache(page);
+
+	address_space = swap_address_space(entry);
+	xa_lock_irq(&address_space->i_pages);
+	for (i = 0; i < nr; i++) {
+		set_page_private(page + i, entry.val + i);
+		error = radix_tree_insert(&address_space->i_pages,
+					  idx + i, page + i);
+		if (unlikely(error))
+			break;
+	}
+	if (likely(!error)) {
+		address_space->nrpages += nr;
+		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
+		ADD_CACHE_INFO(add_total, nr);
+	} else {
+		/*
+		 * 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 + i, 0UL);
+		while (i--) {
+			radix_tree_delete(&address_space->i_pages, idx + i);
+			set_page_private(page + i, 0UL);
+		}
+		ClearPageSwapCache(page);
+		page_ref_sub(page, nr);
+	}
+	xa_unlock_irq(&address_space->i_pages);
+
+	return error;
+}
+
+
+int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
+{
+	int error;
+
+	error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
+	if (!error) {
+		error = __add_to_swap_cache(page, entry);
+		radix_tree_preload_end();
+	}
+	return error;
+}
+
+/*
+ * This must be called only on pages that have
+ * been verified to be in the swap cache.
+ */
+void __delete_from_swap_cache(struct page *page)
+{
+	struct address_space *address_space;
+	int i, nr = hpage_nr_pages(page);
+	swp_entry_t entry;
+	pgoff_t idx;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
+	VM_BUG_ON_PAGE(PageWriteback(page), page);
+
+	entry.val = page_private(page);
+	address_space = swap_address_space(entry);
+	idx = swp_offset(entry);
+	for (i = 0; i < nr; i++) {
+		radix_tree_delete(&address_space->i_pages, idx + i);
+		set_page_private(page + i, 0);
+	}
+	ClearPageSwapCache(page);
+	address_space->nrpages -= nr;
+	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
+	ADD_CACHE_INFO(del_total, nr);
+}
+
+/**
+ * add_to_swap - allocate swap space for a page
+ * @page: page we want to move to swap
+ *
+ * Allocate swap space for the page and add the page to the
+ * swap cache.  Caller needs to hold the page lock. 
+ */
+int add_to_swap(struct page *page)
+{
+	swp_entry_t entry;
+	int err;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageUptodate(page), page);
+
+	entry = get_swap_page(page);
+	if (!entry.val)
+		return 0;
+
+	/*
+	 * Radix-tree node allocations from PF_MEMALLOC contexts could
+	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
+	 * stops emergency reserves from being allocated.
+	 *
+	 * TODO: this could cause a theoretical memory reclaim
+	 * deadlock in the swap out path.
+	 */
+	/*
+	 * Add it to the swap cache.
+	 */
+	err = add_to_swap_cache(page, entry,
+			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
+	/* -ENOMEM radix-tree allocation failure */
+	if (err)
+		/*
+		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+		 * clear SWAP_HAS_CACHE flag.
+		 */
+		goto fail;
+	/*
+	 * Normally the page will be dirtied in unmap because its pte should be
+	 * dirty. A special case is MADV_FREE page. The page'e pte could have
+	 * dirty bit cleared but the page's SwapBacked bit is still set because
+	 * clearing the dirty bit and SwapBacked bit has no lock protected. For
+	 * such page, unmap will not set dirty bit for it, so page reclaim will
+	 * not write the page out. This can cause data corruption when the page
+	 * is swap in later. Always setting the dirty bit for the page solves
+	 * the problem.
+	 */
+	set_page_dirty(page);
+
+	return 1;
+
+fail:
+	put_swap_page(page, entry);
+	return 0;
+}
+
+/*
+ * This must be called only on pages that have
+ * been verified to be in the swap cache and locked.
+ * It will never put the page into the free list,
+ * the caller has a reference on the page.
+ */
+void delete_from_swap_cache(struct page *page)
+{
+	swp_entry_t entry;
+	struct address_space *address_space;
+
+	entry.val = page_private(page);
+
+	address_space = swap_address_space(entry);
+	xa_lock_irq(&address_space->i_pages);
+	__delete_from_swap_cache(page);
+	xa_unlock_irq(&address_space->i_pages);
+
+	put_swap_page(page, entry);
+	page_ref_sub(page, hpage_nr_pages(page));
+}
+
+/* 
+ * If we are the only user, then try to free up the swap cache. 
+ * 
+ * Its ok to check for PageSwapCache without the page lock
+ * here because we are going to recheck again inside
+ * try_to_free_swap() _with_ the lock.
+ * 					- Marcelo
+ */
+static inline void free_swap_cache(struct page *page)
+{
+	if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
+		try_to_free_swap(page);
+		unlock_page(page);
+	}
+}
+
+/* 
+ * Perform a free_page(), also freeing any swap cache associated with
+ * this page if it is the last user of the page.
+ */
+void free_page_and_swap_cache(struct page *page)
+{
+	free_swap_cache(page);
+	if (!is_huge_zero_page(page))
+		put_page(page);
+}
+
+/*
+ * Passed an array of pages, drop them all from swapcache and then release
+ * them.  They are removed from the LRU and freed if this is their last use.
+ */
+void free_pages_and_swap_cache(struct page **pages, int nr)
+{
+	struct page **pagep = pages;
+	int i;
+
+	lru_add_drain();
+	for (i = 0; i < nr; i++)
+		free_swap_cache(pagep[i]);
+	release_pages(pagep, nr);
+}
+
+static inline bool swap_use_vma_readahead(void)
+{
+	return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
+}
+
+/*
+ * Lookup a swap entry in the swap cache. A found page will be returned
+ * unlocked and with its refcount incremented - we rely on the kernel
+ * lock getting page table operations atomic even if we drop the page
+ * lock before returning.
+ */
+struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
+			       unsigned long addr)
+{
+	struct page *page;
+
+	page = find_get_page(swap_address_space(entry), swp_offset(entry));
+
+	INC_CACHE_INFO(find_total);
+	if (page) {
+		bool vma_ra = swap_use_vma_readahead();
+		bool readahead;
+
+		INC_CACHE_INFO(find_success);
+		/*
+		 * At the moment, we don't support PG_readahead for anon THP
+		 * so let's bail out rather than confusing the readahead stat.
+		 */
+		if (unlikely(PageTransCompound(page)))
+			return page;
+
+		readahead = TestClearPageReadahead(page);
+		if (vma && vma_ra) {
+			unsigned long ra_val;
+			int win, hits;
+
+			ra_val = GET_SWAP_RA_VAL(vma);
+			win = SWAP_RA_WIN(ra_val);
+			hits = SWAP_RA_HITS(ra_val);
+			if (readahead)
+				hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
+			atomic_long_set(&vma->swap_readahead_info,
+					SWAP_RA_VAL(addr, win, hits));
+		}
+
+		if (readahead) {
+			count_vm_event(SWAP_RA_HIT);
+			if (!vma || !vma_ra)
+				atomic_inc(&swapin_readahead_hits);
+		}
+	}
+
+	return page;
+}
+
+struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
+			struct vm_area_struct *vma, unsigned long addr,
+			bool *new_page_allocated)
+{
+	struct page *found_page, *new_page = NULL;
+	struct address_space *swapper_space = swap_address_space(entry);
+	int err;
+	*new_page_allocated = false;
+
+	do {
+		/*
+		 * First check the swap cache.  Since this is normally
+		 * called after lookup_swap_cache() failed, re-calling
+		 * that would confuse statistics.
+		 */
+		found_page = find_get_page(swapper_space, swp_offset(entry));
+		if (found_page)
+			break;
+
+		/*
+		 * Just skip read ahead for unused swap slot.
+		 * During swap_off when swap_slot_cache is disabled,
+		 * we have to handle the race between putting
+		 * swap entry in swap cache and marking swap slot
+		 * as SWAP_HAS_CACHE.  That's done in later part of code or
+		 * else swap_off will be aborted if we return NULL.
+		 */
+		if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
+			break;
+
+		/*
+		 * Get a new page to read into from swap.
+		 */
+		if (!new_page) {
+			new_page = alloc_page_vma(gfp_mask, vma, addr);
+			if (!new_page)
+				break;		/* Out of memory */
+		}
+
+		/*
+		 * call radix_tree_preload() while we can wait.
+		 */
+		err = radix_tree_maybe_preload(gfp_mask & GFP_RECLAIM_MASK);
+		if (err)
+			break;
+
+		/*
+		 * Swap entry may have been freed since our caller observed it.
+		 */
+		err = swapcache_prepare(entry);
+		if (err == -EEXIST) {
+			radix_tree_preload_end();
+			/*
+			 * We might race against get_swap_page() and stumble
+			 * across a SWAP_HAS_CACHE swap_map entry whose page
+			 * has not been brought into the swapcache yet.
+			 */
+			cond_resched();
+			continue;
+		}
+		if (err) {		/* swp entry is obsolete ? */
+			radix_tree_preload_end();
+			break;
+		}
+
+		/* May fail (-ENOMEM) if radix-tree node allocation failed. */
+		__SetPageLocked(new_page);
+		__SetPageSwapBacked(new_page);
+		err = __add_to_swap_cache(new_page, entry);
+		if (likely(!err)) {
+			radix_tree_preload_end();
+			/*
+			 * Initiate read into locked page and return.
+			 */
+			lru_cache_add_anon(new_page);
+			*new_page_allocated = true;
+			return new_page;
+		}
+		radix_tree_preload_end();
+		__ClearPageLocked(new_page);
+		/*
+		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+		 * clear SWAP_HAS_CACHE flag.
+		 */
+		put_swap_page(new_page, entry);
+	} while (err != -ENOMEM);
+
+	if (new_page)
+		put_page(new_page);
+	return found_page;
+}
+
+/*
+ * Locate a page of swap in physical memory, reserving swap cache space
+ * and reading the disk if it is not already cached.
+ * A failure return means that either the page allocation failed or that
+ * the swap entry is no longer in use.
+ */
+struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
+		struct vm_area_struct *vma, unsigned long addr, bool do_poll)
+{
+	bool page_was_allocated;
+	struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
+			vma, addr, &page_was_allocated);
+
+	if (page_was_allocated)
+		swap_readpage(retpage, do_poll);
+
+	return retpage;
+}
+
+static unsigned int __swapin_nr_pages(unsigned long prev_offset,
+				      unsigned long offset,
+				      int hits,
+				      int max_pages,
+				      int prev_win)
+{
+	unsigned int pages, last_ra;
+
+	/*
+	 * This heuristic has been found to work well on both sequential and
+	 * random loads, swapping to hard disk or to SSD: please don't ask
+	 * what the "+ 2" means, it just happens to work well, that's all.
+	 */
+	pages = hits + 2;
+	if (pages == 2) {
+		/*
+		 * We can have no readahead hits to judge by: but must not get
+		 * stuck here forever, so check for an adjacent offset instead
+		 * (and don't even bother to check whether swap type is same).
+		 */
+		if (offset != prev_offset + 1 && offset != prev_offset - 1)
+			pages = 1;
+	} else {
+		unsigned int roundup = 4;
+		while (roundup < pages)
+			roundup <<= 1;
+		pages = roundup;
+	}
+
+	if (pages > max_pages)
+		pages = max_pages;
+
+	/* Don't shrink readahead too fast */
+	last_ra = prev_win / 2;
+	if (pages < last_ra)
+		pages = last_ra;
+
+	return pages;
+}
+
+static unsigned long swapin_nr_pages(unsigned long offset)
+{
+	static unsigned long prev_offset;
+	unsigned int hits, pages, max_pages;
+	static atomic_t last_readahead_pages;
+
+	max_pages = 1 << READ_ONCE(page_cluster);
+	if (max_pages <= 1)
+		return 1;
+
+	hits = atomic_xchg(&swapin_readahead_hits, 0);
+	pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
+				  max_pages,
+				  atomic_read(&last_readahead_pages));
+	if (!hits)
+		WRITE_ONCE(prev_offset, offset);
+	atomic_set(&last_readahead_pages, pages);
+
+	return pages;
+}
+
+/**
+ * swap_cluster_readahead - swap in pages in hope we need them soon
+ * @entry: swap entry of this memory
+ * @gfp_mask: memory allocation flags
+ * @vmf: fault information
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * Primitive swap readahead code. We simply read an aligned block of
+ * (1 << page_cluster) entries in the swap area. This method is chosen
+ * because it doesn't cost us any seek time.  We also make sure to queue
+ * the 'original' request together with the readahead ones...
+ *
+ * This has been extended to use the NUMA policies from the mm triggering
+ * the readahead.
+ *
+ * Caller must hold down_read on the vma->vm_mm if vmf->vma is not NULL.
+ */
+struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
+				struct vm_fault *vmf)
+{
+	struct page *page;
+	unsigned long entry_offset = swp_offset(entry);
+	unsigned long offset = entry_offset;
+	unsigned long start_offset, end_offset;
+	unsigned long mask;
+	struct swap_info_struct *si = swp_swap_info(entry);
+	struct blk_plug plug;
+	bool do_poll = true, page_allocated;
+	struct vm_area_struct *vma = vmf->vma;
+	unsigned long addr = vmf->address;
+
+	mask = swapin_nr_pages(offset) - 1;
+	if (!mask)
+		goto skip;
+
+	do_poll = false;
+	/* Read a page_cluster sized and aligned cluster around offset. */
+	start_offset = offset & ~mask;
+	end_offset = offset | mask;
+	if (!start_offset)	/* First page is swap header. */
+		start_offset++;
+	if (end_offset >= si->max)
+		end_offset = si->max - 1;
+
+	blk_start_plug(&plug);
+	for (offset = start_offset; offset <= end_offset ; offset++) {
+		/* Ok, do the async read-ahead now */
+		page = __read_swap_cache_async(
+			swp_entry(swp_type(entry), offset),
+			gfp_mask, vma, addr, &page_allocated);
+		if (!page)
+			continue;
+		if (page_allocated) {
+			swap_readpage(page, false);
+			if (offset != entry_offset) {
+				SetPageReadahead(page);
+				count_vm_event(SWAP_RA);
+			}
+		}
+		put_page(page);
+	}
+	blk_finish_plug(&plug);
+
+	lru_add_drain();	/* Push any new pages onto the LRU now */
+skip:
+	return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
+}
+
+int init_swap_address_space(unsigned int type, unsigned long nr_pages)
+{
+	struct address_space *spaces, *space;
+	unsigned int i, nr;
+
+	nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
+	spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
+	if (!spaces)
+		return -ENOMEM;
+	for (i = 0; i < nr; i++) {
+		space = spaces + i;
+		INIT_RADIX_TREE(&space->i_pages, GFP_ATOMIC|__GFP_NOWARN);
+		atomic_set(&space->i_mmap_writable, 0);
+		space->a_ops = &swap_aops;
+		/* swap cache doesn't use writeback related tags */
+		mapping_set_no_writeback_tags(space);
+	}
+	nr_swapper_spaces[type] = nr;
+	rcu_assign_pointer(swapper_spaces[type], spaces);
+
+	return 0;
+}
+
+void exit_swap_address_space(unsigned int type)
+{
+	struct address_space *spaces;
+
+	spaces = swapper_spaces[type];
+	nr_swapper_spaces[type] = 0;
+	rcu_assign_pointer(swapper_spaces[type], NULL);
+	synchronize_rcu();
+	kvfree(spaces);
+}
+
+static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
+				     unsigned long faddr,
+				     unsigned long lpfn,
+				     unsigned long rpfn,
+				     unsigned long *start,
+				     unsigned long *end)
+{
+	*start = max3(lpfn, PFN_DOWN(vma->vm_start),
+		      PFN_DOWN(faddr & PMD_MASK));
+	*end = min3(rpfn, PFN_DOWN(vma->vm_end),
+		    PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
+}
+
+static void swap_ra_info(struct vm_fault *vmf,
+			struct vma_swap_readahead *ra_info)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	unsigned long ra_val;
+	swp_entry_t entry;
+	unsigned long faddr, pfn, fpfn;
+	unsigned long start, end;
+	pte_t *pte, *orig_pte;
+	unsigned int max_win, hits, prev_win, win, left;
+#ifndef CONFIG_64BIT
+	pte_t *tpte;
+#endif
+
+	max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
+			     SWAP_RA_ORDER_CEILING);
+	if (max_win == 1) {
+		ra_info->win = 1;
+		return;
+	}
+
+	faddr = vmf->address;
+	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
+	entry = pte_to_swp_entry(*pte);
+	if ((unlikely(non_swap_entry(entry)))) {
+		pte_unmap(orig_pte);
+		return;
+	}
+
+	fpfn = PFN_DOWN(faddr);
+	ra_val = GET_SWAP_RA_VAL(vma);
+	pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
+	prev_win = SWAP_RA_WIN(ra_val);
+	hits = SWAP_RA_HITS(ra_val);
+	ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
+					       max_win, prev_win);
+	atomic_long_set(&vma->swap_readahead_info,
+			SWAP_RA_VAL(faddr, win, 0));
+
+	if (win == 1) {
+		pte_unmap(orig_pte);
+		return;
+	}
+
+	/* Copy the PTEs because the page table may be unmapped */
+	if (fpfn == pfn + 1)
+		swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
+	else if (pfn == fpfn + 1)
+		swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
+				  &start, &end);
+	else {
+		left = (win - 1) / 2;
+		swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
+				  &start, &end);
+	}
+	ra_info->nr_pte = end - start;
+	ra_info->offset = fpfn - start;
+	pte -= ra_info->offset;
+#ifdef CONFIG_64BIT
+	ra_info->ptes = pte;
+#else
+	tpte = ra_info->ptes;
+	for (pfn = start; pfn != end; pfn++)
+		*tpte++ = *pte++;
+#endif
+	pte_unmap(orig_pte);
+}
+
+static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
+				       struct vm_fault *vmf)
+{
+	struct blk_plug plug;
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page;
+	pte_t *pte, pentry;
+	swp_entry_t entry;
+	unsigned int i;
+	bool page_allocated;
+	struct vma_swap_readahead ra_info = {0,};
+
+	swap_ra_info(vmf, &ra_info);
+	if (ra_info.win == 1)
+		goto skip;
+
+	blk_start_plug(&plug);
+	for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
+	     i++, pte++) {
+		pentry = *pte;
+		if (pte_none(pentry))
+			continue;
+		if (pte_present(pentry))
+			continue;
+		entry = pte_to_swp_entry(pentry);
+		if (unlikely(non_swap_entry(entry)))
+			continue;
+		page = __read_swap_cache_async(entry, gfp_mask, vma,
+					       vmf->address, &page_allocated);
+		if (!page)
+			continue;
+		if (page_allocated) {
+			swap_readpage(page, false);
+			if (i != ra_info.offset) {
+				SetPageReadahead(page);
+				count_vm_event(SWAP_RA);
+			}
+		}
+		put_page(page);
+	}
+	blk_finish_plug(&plug);
+	lru_add_drain();
+skip:
+	return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
+				     ra_info.win == 1);
+}
+
+/**
+ * swapin_readahead - swap in pages in hope we need them soon
+ * @entry: swap entry of this memory
+ * @gfp_mask: memory allocation flags
+ * @vmf: fault information
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * It's a main entry function for swap readahead. By the configuration,
+ * it will read ahead blocks by cluster-based(ie, physical disk based)
+ * or vma-based(ie, virtual address based on faulty address) readahead.
+ */
+struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
+				struct vm_fault *vmf)
+{
+	return swap_use_vma_readahead() ?
+			swap_vma_readahead(entry, gfp_mask, vmf) :
+			swap_cluster_readahead(entry, gfp_mask, vmf);
+}
+
+#ifdef CONFIG_SYSFS
+static ssize_t vma_ra_enabled_show(struct kobject *kobj,
+				     struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%s\n", enable_vma_readahead ? "true" : "false");
+}
+static ssize_t vma_ra_enabled_store(struct kobject *kobj,
+				      struct kobj_attribute *attr,
+				      const char *buf, size_t count)
+{
+	if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
+		enable_vma_readahead = true;
+	else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
+		enable_vma_readahead = false;
+	else
+		return -EINVAL;
+
+	return count;
+}
+static struct kobj_attribute vma_ra_enabled_attr =
+	__ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
+	       vma_ra_enabled_store);
+
+static struct attribute *swap_attrs[] = {
+	&vma_ra_enabled_attr.attr,
+	NULL,
+};
+
+static struct attribute_group swap_attr_group = {
+	.attrs = swap_attrs,
+};
+
+static int __init swap_init_sysfs(void)
+{
+	int err;
+	struct kobject *swap_kobj;
+
+	swap_kobj = kobject_create_and_add("swap", mm_kobj);
+	if (!swap_kobj) {
+		pr_err("failed to create swap kobject\n");
+		return -ENOMEM;
+	}
+	err = sysfs_create_group(swap_kobj, &swap_attr_group);
+	if (err) {
+		pr_err("failed to register swap group\n");
+		goto delete_obj;
+	}
+	return 0;
+
+delete_obj:
+	kobject_put(swap_kobj);
+	return err;
+}
+subsys_initcall(swap_init_sysfs);
+#endif