upload tizen1.0 sourceHEADmaster2.0alpha

1 files changed, 2512 insertions, 0 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
new file mode 100644
index 00000000..7c703ff2
--- /dev/null
+++ b/mm/swapfile.c
@@ -0,0 +1,2512 @@
+/*
+ *  linux/mm/swapfile.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *  Swap reorganised 29.12.95, Stephen Tweedie
+ */
+
+#include <linux/mm.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/slab.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/vmalloc.h>
+#include <linux/pagemap.h>
+#include <linux/namei.h>
+#include <linux/shm.h>
+#include <linux/blkdev.h>
+#include <linux/random.h>
+#include <linux/writeback.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/ksm.h>
+#include <linux/rmap.h>
+#include <linux/security.h>
+#include <linux/backing-dev.h>
+#include <linux/mutex.h>
+#include <linux/capability.h>
+#include <linux/syscalls.h>
+#include <linux/memcontrol.h>
+
+#include <asm/pgtable.h>
+#include <asm/tlbflush.h>
+#include <linux/swapops.h>
+#include <linux/page_cgroup.h>
+
+static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
+				 unsigned char);
+static void free_swap_count_continuations(struct swap_info_struct *);
+static sector_t map_swap_entry(swp_entry_t, struct block_device**);
+
+static DEFINE_SPINLOCK(swap_lock);
+static unsigned int nr_swapfiles;
+long nr_swap_pages;
+long total_swap_pages;
+static int least_priority;
+
+static const char Bad_file[] = "Bad swap file entry ";
+static const char Unused_file[] = "Unused swap file entry ";
+static const char Bad_offset[] = "Bad swap offset entry ";
+static const char Unused_offset[] = "Unused swap offset entry ";
+
+static struct swap_list_t swap_list = {-1, -1};
+
+static struct swap_info_struct *swap_info[MAX_SWAPFILES];
+
+static DEFINE_MUTEX(swapon_mutex);
+
+static inline unsigned char swap_count(unsigned char ent)
+{
+	return ent & ~SWAP_HAS_CACHE;	/* may include SWAP_HAS_CONT flag */
+}
+
+/* returns 1 if swap entry is freed */
+static int
+__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
+{
+	swp_entry_t entry = swp_entry(si->type, offset);
+	struct page *page;
+	int ret = 0;
+
+	page = find_get_page(&swapper_space, entry.val);
+	if (!page)
+		return 0;
+	/*
+	 * This function is called from scan_swap_map() and it's called
+	 * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
+	 * We have to use trylock for avoiding deadlock. This is a special
+	 * case and you should use try_to_free_swap() with explicit lock_page()
+	 * in usual operations.
+	 */
+	if (trylock_page(page)) {
+		ret = try_to_free_swap(page);
+		unlock_page(page);
+	}
+	page_cache_release(page);
+	return ret;
+}
+
+/*
+ * We need this because the bdev->unplug_fn can sleep and we cannot
+ * hold swap_lock while calling the unplug_fn. And swap_lock
+ * cannot be turned into a mutex.
+ */
+static DECLARE_RWSEM(swap_unplug_sem);
+
+void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
+{
+	swp_entry_t entry;
+
+	down_read(&swap_unplug_sem);
+	entry.val = page_private(page);
+	if (PageSwapCache(page)) {
+		struct block_device *bdev = swap_info[swp_type(entry)]->bdev;
+		struct backing_dev_info *bdi;
+
+		/*
+		 * If the page is removed from swapcache from under us (with a
+		 * racy try_to_unuse/swapoff) we need an additional reference
+		 * count to avoid reading garbage from page_private(page) above.
+		 * If the WARN_ON triggers during a swapoff it maybe the race
+		 * condition and it's harmless. However if it triggers without
+		 * swapoff it signals a problem.
+		 */
+		WARN_ON(page_count(page) <= 1);
+
+		bdi = bdev->bd_inode->i_mapping->backing_dev_info;
+		blk_run_backing_dev(bdi, page);
+	}
+	up_read(&swap_unplug_sem);
+}
+
+/*
+ * swapon tell device that all the old swap contents can be discarded,
+ * to allow the swap device to optimize its wear-levelling.
+ */
+static int discard_swap(struct swap_info_struct *si)
+{
+	struct swap_extent *se;
+	sector_t start_block;
+	sector_t nr_blocks;
+	int err = 0;
+
+	/* Do not discard the swap header page! */
+	se = &si->first_swap_extent;
+	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
+	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
+	if (nr_blocks) {
+		err = blkdev_issue_discard(si->bdev, start_block,
+				nr_blocks, GFP_KERNEL, BLKDEV_IFL_WAIT);
+		if (err)
+			return err;
+		cond_resched();
+	}
+
+	list_for_each_entry(se, &si->first_swap_extent.list, list) {
+		start_block = se->start_block << (PAGE_SHIFT - 9);
+		nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
+
+		err = blkdev_issue_discard(si->bdev, start_block,
+				nr_blocks, GFP_KERNEL, BLKDEV_IFL_WAIT);
+		if (err)
+			break;
+
+		cond_resched();
+	}
+	return err;		/* That will often be -EOPNOTSUPP */
+}
+
+/*
+ * swap allocation tell device that a cluster of swap can now be discarded,
+ * to allow the swap device to optimize its wear-levelling.
+ */
+static void discard_swap_cluster(struct swap_info_struct *si,
+				 pgoff_t start_page, pgoff_t nr_pages)
+{
+	struct swap_extent *se = si->curr_swap_extent;
+	int found_extent = 0;
+
+	while (nr_pages) {
+		struct list_head *lh;
+
+		if (se->start_page <= start_page &&
+		    start_page < se->start_page + se->nr_pages) {
+			pgoff_t offset = start_page - se->start_page;
+			sector_t start_block = se->start_block + offset;
+			sector_t nr_blocks = se->nr_pages - offset;
+
+			if (nr_blocks > nr_pages)
+				nr_blocks = nr_pages;
+			start_page += nr_blocks;
+			nr_pages -= nr_blocks;
+
+			if (!found_extent++)
+				si->curr_swap_extent = se;
+
+			start_block <<= PAGE_SHIFT - 9;
+			nr_blocks <<= PAGE_SHIFT - 9;
+			if (blkdev_issue_discard(si->bdev, start_block,
+				    nr_blocks, GFP_NOIO, BLKDEV_IFL_WAIT))
+				break;
+		}
+
+		lh = se->list.next;
+		se = list_entry(lh, struct swap_extent, list);
+	}
+}
+
+static int wait_for_discard(void *word)
+{
+	schedule();
+	return 0;
+}
+
+#define SWAPFILE_CLUSTER	256
+#define LATENCY_LIMIT		256
+
+static inline unsigned long scan_swap_map(struct swap_info_struct *si,
+					  unsigned char usage)
+{
+	unsigned long offset;
+	unsigned long scan_base;
+	unsigned long last_in_cluster = 0;
+	int latency_ration = LATENCY_LIMIT;
+	int found_free_cluster = 0;
+
+	/*
+	 * We try to cluster swap pages by allocating them sequentially
+	 * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
+	 * way, however, we resort to first-free allocation, starting
+	 * a new cluster.  This prevents us from scattering swap pages
+	 * all over the entire swap partition, so that we reduce
+	 * overall disk seek times between swap pages.  -- sct
+	 * But we do now try to find an empty cluster.  -Andrea
+	 * And we let swap pages go all over an SSD partition.  Hugh
+	 */
+
+	si->flags += SWP_SCANNING;
+	scan_base = offset = si->cluster_next;
+
+	if (unlikely(!si->cluster_nr--)) {
+		if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
+			si->cluster_nr = SWAPFILE_CLUSTER - 1;
+			goto checks;
+		}
+		if (si->flags & SWP_DISCARDABLE) {
+			/*
+			 * Start range check on racing allocations, in case
+			 * they overlap the cluster we eventually decide on
+			 * (we scan without swap_lock to allow preemption).
+			 * It's hardly conceivable that cluster_nr could be
+			 * wrapped during our scan, but don't depend on it.
+			 */
+			if (si->lowest_alloc)
+				goto checks;
+			si->lowest_alloc = si->max;
+			si->highest_alloc = 0;
+		}
+		spin_unlock(&swap_lock);
+
+		/*
+		 * If seek is expensive, start searching for new cluster from
+		 * start of partition, to minimize the span of allocated swap.
+		 * But if seek is cheap, search from our current position, so
+		 * that swap is allocated from all over the partition: if the
+		 * Flash Translation Layer only remaps within limited zones,
+		 * we don't want to wear out the first zone too quickly.
+		 */
+		if (!(si->flags & SWP_SOLIDSTATE))
+			scan_base = offset = si->lowest_bit;
+		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
+
+		/* Locate the first empty (unaligned) cluster */
+		for (; last_in_cluster <= si->highest_bit; offset++) {
+			if (si->swap_map[offset])
+				last_in_cluster = offset + SWAPFILE_CLUSTER;
+			else if (offset == last_in_cluster) {
+				spin_lock(&swap_lock);
+				offset -= SWAPFILE_CLUSTER - 1;
+				si->cluster_next = offset;
+				si->cluster_nr = SWAPFILE_CLUSTER - 1;
+				found_free_cluster = 1;
+				goto checks;
+			}
+			if (unlikely(--latency_ration < 0)) {
+				cond_resched();
+				latency_ration = LATENCY_LIMIT;
+			}
+		}
+
+		offset = si->lowest_bit;
+		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
+
+		/* Locate the first empty (unaligned) cluster */
+		for (; last_in_cluster < scan_base; offset++) {
+			if (si->swap_map[offset])
+				last_in_cluster = offset + SWAPFILE_CLUSTER;
+			else if (offset == last_in_cluster) {
+				spin_lock(&swap_lock);
+				offset -= SWAPFILE_CLUSTER - 1;
+				si->cluster_next = offset;
+				si->cluster_nr = SWAPFILE_CLUSTER - 1;
+				found_free_cluster = 1;
+				goto checks;
+			}
+			if (unlikely(--latency_ration < 0)) {
+				cond_resched();
+				latency_ration = LATENCY_LIMIT;
+			}
+		}
+
+		offset = scan_base;
+		spin_lock(&swap_lock);
+		si->cluster_nr = SWAPFILE_CLUSTER - 1;
+		si->lowest_alloc = 0;
+	}
+
+checks:
+	if (!(si->flags & SWP_WRITEOK))
+		goto no_page;
+	if (!si->highest_bit)
+		goto no_page;
+	if (offset > si->highest_bit)
+		scan_base = offset = si->lowest_bit;
+
+	/* reuse swap entry of cache-only swap if not busy. */
+	if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+		int swap_was_freed;
+		spin_unlock(&swap_lock);
+		swap_was_freed = __try_to_reclaim_swap(si, offset);
+		spin_lock(&swap_lock);
+		/* entry was freed successfully, try to use this again */
+		if (swap_was_freed)
+			goto checks;
+		goto scan; /* check next one */
+	}
+
+	if (si->swap_map[offset])
+		goto scan;
+
+	if (offset == si->lowest_bit)
+		si->lowest_bit++;
+	if (offset == si->highest_bit)
+		si->highest_bit--;
+	si->inuse_pages++;
+	if (si->inuse_pages == si->pages) {
+		si->lowest_bit = si->max;
+		si->highest_bit = 0;
+	}
+	si->swap_map[offset] = usage;
+	si->cluster_next = offset + 1;
+	si->flags -= SWP_SCANNING;
+
+	if (si->lowest_alloc) {
+		/*
+		 * Only set when SWP_DISCARDABLE, and there's a scan
+		 * for a free cluster in progress or just completed.
+		 */
+		if (found_free_cluster) {
+			/*
+			 * To optimize wear-levelling, discard the
+			 * old data of the cluster, taking care not to
+			 * discard any of its pages that have already
+			 * been allocated by racing tasks (offset has
+			 * already stepped over any at the beginning).
+			 */
+			if (offset < si->highest_alloc &&
+			    si->lowest_alloc <= last_in_cluster)
+				last_in_cluster = si->lowest_alloc - 1;
+			si->flags |= SWP_DISCARDING;
+			spin_unlock(&swap_lock);
+
+			if (offset < last_in_cluster)
+				discard_swap_cluster(si, offset,
+					last_in_cluster - offset + 1);
+
+			spin_lock(&swap_lock);
+			si->lowest_alloc = 0;
+			si->flags &= ~SWP_DISCARDING;
+
+			smp_mb();	/* wake_up_bit advises this */
+			wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
+
+		} else if (si->flags & SWP_DISCARDING) {
+			/*
+			 * Delay using pages allocated by racing tasks
+			 * until the whole discard has been issued. We
+			 * could defer that delay until swap_writepage,
+			 * but it's easier to keep this self-contained.
+			 */
+			spin_unlock(&swap_lock);
+			wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
+				wait_for_discard, TASK_UNINTERRUPTIBLE);
+			spin_lock(&swap_lock);
+		} else {
+			/*
+			 * Note pages allocated by racing tasks while
+			 * scan for a free cluster is in progress, so
+			 * that its final discard can exclude them.
+			 */
+			if (offset < si->lowest_alloc)
+				si->lowest_alloc = offset;
+			if (offset > si->highest_alloc)
+				si->highest_alloc = offset;
+		}
+	}
+	return offset;
+
+scan:
+	spin_unlock(&swap_lock);
+	while (++offset <= si->highest_bit) {
+		if (!si->swap_map[offset]) {
+			spin_lock(&swap_lock);
+			goto checks;
+		}
+		if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+			spin_lock(&swap_lock);
+			goto checks;
+		}
+		if (unlikely(--latency_ration < 0)) {
+			cond_resched();
+			latency_ration = LATENCY_LIMIT;
+		}
+	}
+	offset = si->lowest_bit;
+	while (++offset < scan_base) {
+		if (!si->swap_map[offset]) {
+			spin_lock(&swap_lock);
+			goto checks;
+		}
+		if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
+			spin_lock(&swap_lock);
+			goto checks;
+		}
+		if (unlikely(--latency_ration < 0)) {
+			cond_resched();
+			latency_ration = LATENCY_LIMIT;
+		}
+	}
+	spin_lock(&swap_lock);
+
+no_page:
+	si->flags -= SWP_SCANNING;
+	return 0;
+}
+
+swp_entry_t get_swap_page(void)
+{
+	struct swap_info_struct *si;
+	pgoff_t offset;
+	int type, next;
+	int wrapped = 0;
+
+	spin_lock(&swap_lock);
+	if (nr_swap_pages <= 0)
+		goto noswap;
+	nr_swap_pages--;
+
+	for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
+		si = swap_info[type];
+		next = si->next;
+		if (next < 0 ||
+		    (!wrapped && si->prio != swap_info[next]->prio)) {
+			next = swap_list.head;
+			wrapped++;
+		}
+
+		if (!si->highest_bit)
+			continue;
+		if (!(si->flags & SWP_WRITEOK))
+			continue;
+
+		swap_list.next = next;
+		/* This is called for allocating swap entry for cache */
+		offset = scan_swap_map(si, SWAP_HAS_CACHE);
+		if (offset) {
+			spin_unlock(&swap_lock);
+			return swp_entry(type, offset);
+		}
+		next = swap_list.next;
+	}
+
+	nr_swap_pages++;
+noswap:
+	spin_unlock(&swap_lock);
+	return (swp_entry_t) {0};
+}
+
+/* The only caller of this function is now susupend routine */
+swp_entry_t get_swap_page_of_type(int type)
+{
+	struct swap_info_struct *si;
+	pgoff_t offset;
+
+	spin_lock(&swap_lock);
+	si = swap_info[type];
+	if (si && (si->flags & SWP_WRITEOK)) {
+		nr_swap_pages--;
+		/* This is called for allocating swap entry, not cache */
+		offset = scan_swap_map(si, 1);
+		if (offset) {
+			spin_unlock(&swap_lock);
+			return swp_entry(type, offset);
+		}
+		nr_swap_pages++;
+	}
+	spin_unlock(&swap_lock);
+	return (swp_entry_t) {0};
+}
+
+static struct swap_info_struct *swap_info_get(swp_entry_t entry)
+{
+	struct swap_info_struct *p;
+	unsigned long offset, type;
+
+	if (!entry.val)
+		goto out;
+	type = swp_type(entry);
+	if (type >= nr_swapfiles)
+		goto bad_nofile;
+	p = swap_info[type];
+	if (!(p->flags & SWP_USED))
+		goto bad_device;
+	offset = swp_offset(entry);
+	if (offset >= p->max)
+		goto bad_offset;
+	if (!p->swap_map[offset])
+		goto bad_free;
+	spin_lock(&swap_lock);
+	return p;
+
+bad_free:
+	printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
+	goto out;
+bad_offset:
+	printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
+	goto out;
+bad_device:
+	printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
+	goto out;
+bad_nofile:
+	printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
+out:
+	return NULL;
+}
+
+static unsigned char swap_entry_free(struct swap_info_struct *p,
+				     swp_entry_t entry, unsigned char usage)
+{
+	unsigned long offset = swp_offset(entry);
+	unsigned char count;
+	unsigned char has_cache;
+
+	count = p->swap_map[offset];
+	has_cache = count & SWAP_HAS_CACHE;
+	count &= ~SWAP_HAS_CACHE;
+
+	if (usage == SWAP_HAS_CACHE) {
+		VM_BUG_ON(!has_cache);
+		has_cache = 0;
+	} else if (count == SWAP_MAP_SHMEM) {
+		/*
+		 * Or we could insist on shmem.c using a special
+		 * swap_shmem_free() and free_shmem_swap_and_cache()...
+		 */
+		count = 0;
+	} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
+		if (count == COUNT_CONTINUED) {
+			if (swap_count_continued(p, offset, count))
+				count = SWAP_MAP_MAX | COUNT_CONTINUED;
+			else
+				count = SWAP_MAP_MAX;
+		} else
+			count--;
+	}
+
+	if (!count)
+		mem_cgroup_uncharge_swap(entry);
+
+	usage = count | has_cache;
+	p->swap_map[offset] = usage;
+
+	/* free if no reference */
+	if (!usage) {
+		struct gendisk *disk = p->bdev->bd_disk;
+		if (offset < p->lowest_bit)
+			p->lowest_bit = offset;
+		if (offset > p->highest_bit)
+			p->highest_bit = offset;
+		if (swap_list.next >= 0 &&
+		    p->prio > swap_info[swap_list.next]->prio)
+			swap_list.next = p->type;
+		nr_swap_pages++;
+		p->inuse_pages--;
+		if ((p->flags & SWP_BLKDEV) &&
+				disk->fops->swap_slot_free_notify)
+			disk->fops->swap_slot_free_notify(p->bdev, offset);
+	}
+
+	return usage;
+}
+
+/*
+ * Caller has made sure that the swapdevice corresponding to entry
+ * is still around or has not been recycled.
+ */
+void swap_free(swp_entry_t entry)
+{
+	struct swap_info_struct *p;
+
+	p = swap_info_get(entry);
+	if (p) {
+		swap_entry_free(p, entry, 1);
+		spin_unlock(&swap_lock);
+	}
+}
+
+/*
+ * Called after dropping swapcache to decrease refcnt to swap entries.
+ */
+void swapcache_free(swp_entry_t entry, struct page *page)
+{
+	struct swap_info_struct *p;
+	unsigned char count;
+
+	p = swap_info_get(entry);
+	if (p) {
+		count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
+		if (page)
+			mem_cgroup_uncharge_swapcache(page, entry, count != 0);
+		spin_unlock(&swap_lock);
+	}
+}
+
+/*
+ * How many references to page are currently swapped out?
+ * This does not give an exact answer when swap count is continued,
+ * but does include the high COUNT_CONTINUED flag to allow for that.
+ */
+static inline int page_swapcount(struct page *page)
+{
+	int count = 0;
+	struct swap_info_struct *p;
+	swp_entry_t entry;
+
+	entry.val = page_private(page);
+	p = swap_info_get(entry);
+	if (p) {
+		count = swap_count(p->swap_map[swp_offset(entry)]);
+		spin_unlock(&swap_lock);
+	}
+	return count;
+}
+
+/*
+ * We can write to an anon page without COW if there are no other references
+ * to it.  And as a side-effect, free up its swap: because the old content
+ * on disk will never be read, and seeking back there to write new content
+ * later would only waste time away from clustering.
+ */
+int reuse_swap_page(struct page *page)
+{
+	int count;
+
+	VM_BUG_ON(!PageLocked(page));
+	if (unlikely(PageKsm(page)))
+		return 0;
+	count = page_mapcount(page);
+	if (count <= 1 && PageSwapCache(page)) {
+		count += page_swapcount(page);
+		if (count == 1 && !PageWriteback(page)) {
+			delete_from_swap_cache(page);
+			SetPageDirty(page);
+		}
+	}
+	return count <= 1;
+}
+
+/*
+ * If swap is getting full, or if there are no more mappings of this page,
+ * then try_to_free_swap is called to free its swap space.
+ */
+int try_to_free_swap(struct page *page)
+{
+	VM_BUG_ON(!PageLocked(page));
+
+	if (!PageSwapCache(page))
+		return 0;
+	if (PageWriteback(page))
+		return 0;
+	if (page_swapcount(page))
+		return 0;
+
+	/*
+	 * Once hibernation has begun to create its image of memory,
+	 * there's a danger that one of the calls to try_to_free_swap()
+	 * - most probably a call from __try_to_reclaim_swap() while
+	 * hibernation is allocating its own swap pages for the image,
+	 * but conceivably even a call from memory reclaim - will free
+	 * the swap from a page which has already been recorded in the
+	 * image as a clean swapcache page, and then reuse its swap for
+	 * another page of the image.  On waking from hibernation, the
+	 * original page might be freed under memory pressure, then
+	 * later read back in from swap, now with the wrong data.
+	 *
+	 * Hibernation clears bits from gfp_allowed_mask to prevent
+	 * memory reclaim from writing to disk, so check that here.
+	 */
+	if (!(gfp_allowed_mask & __GFP_IO))
+		return 0;
+
+	delete_from_swap_cache(page);
+	SetPageDirty(page);
+	return 1;
+}
+
+/*
+ * Free the swap entry like above, but also try to
+ * free the page cache entry if it is the last user.
+ */
+int free_swap_and_cache(swp_entry_t entry)
+{
+	struct swap_info_struct *p;
+	struct page *page = NULL;
+
+	if (non_swap_entry(entry))
+		return 1;
+
+	p = swap_info_get(entry);
+	if (p) {
+		if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
+			page = find_get_page(&swapper_space, entry.val);
+			if (page && !trylock_page(page)) {
+				page_cache_release(page);
+				page = NULL;
+			}
+		}
+		spin_unlock(&swap_lock);
+	}
+	if (page) {
+		/*
+		 * Not mapped elsewhere, or swap space full? Free it!
+		 * Also recheck PageSwapCache now page is locked (above).
+		 */
+		if (PageSwapCache(page) && !PageWriteback(page) &&
+				(!page_mapped(page) || vm_swap_full())) {
+			delete_from_swap_cache(page);
+			SetPageDirty(page);
+		}
+		unlock_page(page);
+		page_cache_release(page);
+	}
+	return p != NULL;
+}
+
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+/**
+ * mem_cgroup_count_swap_user - count the user of a swap entry
+ * @ent: the swap entry to be checked
+ * @pagep: the pointer for the swap cache page of the entry to be stored
+ *
+ * Returns the number of the user of the swap entry. The number is valid only
+ * for swaps of anonymous pages.
+ * If the entry is found on swap cache, the page is stored to pagep with
+ * refcount of it being incremented.
+ */
+int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
+{
+	struct page *page;
+	struct swap_info_struct *p;
+	int count = 0;
+
+	page = find_get_page(&swapper_space, ent.val);
+	if (page)
+		count += page_mapcount(page);
+	p = swap_info_get(ent);
+	if (p) {
+		count += swap_count(p->swap_map[swp_offset(ent)]);
+		spin_unlock(&swap_lock);
+	}
+
+	*pagep = page;
+	return count;
+}
+#endif
+
+#ifdef CONFIG_HIBERNATION
+/*
+ * Find the swap type that corresponds to given device (if any).
+ *
+ * @offset - number of the PAGE_SIZE-sized block of the device, starting
+ * from 0, in which the swap header is expected to be located.
+ *
+ * This is needed for the suspend to disk (aka swsusp).
+ */
+int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
+{
+	struct block_device *bdev = NULL;
+	int type;
+
+	if (device)
+		bdev = bdget(device);
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		if (!(sis->flags & SWP_WRITEOK))
+			continue;
+
+		if (!bdev) {
+			if (bdev_p)
+				*bdev_p = bdgrab(sis->bdev);
+
+			spin_unlock(&swap_lock);
+			return type;
+		}
+		if (bdev == sis->bdev) {
+			struct swap_extent *se = &sis->first_swap_extent;
+
+			if (se->start_block == offset) {
+				if (bdev_p)
+					*bdev_p = bdgrab(sis->bdev);
+
+				spin_unlock(&swap_lock);
+				bdput(bdev);
+				return type;
+			}
+		}
+	}
+	spin_unlock(&swap_lock);
+	if (bdev)
+		bdput(bdev);
+
+	return -ENODEV;
+}
+
+/*
+ * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
+ * corresponding to given index in swap_info (swap type).
+ */
+sector_t swapdev_block(int type, pgoff_t offset)
+{
+	struct block_device *bdev;
+
+	if ((unsigned int)type >= nr_swapfiles)
+		return 0;
+	if (!(swap_info[type]->flags & SWP_WRITEOK))
+		return 0;
+	return map_swap_entry(swp_entry(type, offset), &bdev);
+}
+
+/*
+ * Return either the total number of swap pages of given type, or the number
+ * of free pages of that type (depending on @free)
+ *
+ * This is needed for software suspend
+ */
+unsigned int count_swap_pages(int type, int free)
+{
+	unsigned int n = 0;
+
+	spin_lock(&swap_lock);
+	if ((unsigned int)type < nr_swapfiles) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		if (sis->flags & SWP_WRITEOK) {
+			n = sis->pages;
+			if (free)
+				n -= sis->inuse_pages;
+		}
+	}
+	spin_unlock(&swap_lock);
+	return n;
+}
+#endif /* CONFIG_HIBERNATION */
+
+/*
+ * No need to decide whether this PTE shares the swap entry with others,
+ * just let do_wp_page work it out if a write is requested later - to
+ * force COW, vm_page_prot omits write permission from any private vma.
+ */
+static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
+		unsigned long addr, swp_entry_t entry, struct page *page)
+{
+	struct mem_cgroup *ptr = NULL;
+	spinlock_t *ptl;
+	pte_t *pte;
+	int ret = 1;
+
+	if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) {
+		ret = -ENOMEM;
+		goto out_nolock;
+	}
+
+	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
+		if (ret > 0)
+			mem_cgroup_cancel_charge_swapin(ptr);
+		ret = 0;
+		goto out;
+	}
+
+	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
+	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
+	get_page(page);
+	set_pte_at(vma->vm_mm, addr, pte,
+		   pte_mkold(mk_pte(page, vma->vm_page_prot)));
+	page_add_anon_rmap(page, vma, addr);
+	mem_cgroup_commit_charge_swapin(page, ptr);
+	swap_free(entry);
+	/*
+	 * Move the page to the active list so it is not
+	 * immediately swapped out again after swapon.
+	 */
+	activate_page(page);
+out:
+	pte_unmap_unlock(pte, ptl);
+out_nolock:
+	return ret;
+}
+
+static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
+				unsigned long addr, unsigned long end,
+				swp_entry_t entry, struct page *page)
+{
+	pte_t swp_pte = swp_entry_to_pte(entry);
+	pte_t *pte;
+	int ret = 0;
+
+	/*
+	 * We don't actually need pte lock while scanning for swp_pte: since
+	 * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
+	 * page table while we're scanning; though it could get zapped, and on
+	 * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
+	 * of unmatched parts which look like swp_pte, so unuse_pte must
+	 * recheck under pte lock.  Scanning without pte lock lets it be
+	 * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
+	 */
+	pte = pte_offset_map(pmd, addr);
+	do {
+		/*
+		 * swapoff spends a _lot_ of time in this loop!
+		 * Test inline before going to call unuse_pte.
+		 */
+		if (unlikely(pte_same(*pte, swp_pte))) {
+			pte_unmap(pte);
+			ret = unuse_pte(vma, pmd, addr, entry, page);
+			if (ret)
+				goto out;
+			pte = pte_offset_map(pmd, addr);
+		}
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+	pte_unmap(pte - 1);
+out:
+	return ret;
+}
+
+static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				swp_entry_t entry, struct page *page)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int ret;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none_or_clear_bad(pmd))
+			continue;
+		ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
+		if (ret)
+			return ret;
+	} while (pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				swp_entry_t entry, struct page *page)
+{
+	pud_t *pud;
+	unsigned long next;
+	int ret;
+
+	pud = pud_offset(pgd, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
+		if (ret)
+			return ret;
+	} while (pud++, addr = next, addr != end);
+	return 0;
+}
+
+static int unuse_vma(struct vm_area_struct *vma,
+				swp_entry_t entry, struct page *page)
+{
+	pgd_t *pgd;
+	unsigned long addr, end, next;
+	int ret;
+
+	if (page_anon_vma(page)) {
+		addr = page_address_in_vma(page, vma);
+		if (addr == -EFAULT)
+			return 0;
+		else
+			end = addr + PAGE_SIZE;
+	} else {
+		addr = vma->vm_start;
+		end = vma->vm_end;
+	}
+
+	pgd = pgd_offset(vma->vm_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
+		if (ret)
+			return ret;
+	} while (pgd++, addr = next, addr != end);
+	return 0;
+}
+
+static int unuse_mm(struct mm_struct *mm,
+				swp_entry_t entry, struct page *page)
+{
+	struct vm_area_struct *vma;
+	int ret = 0;
+
+	if (!down_read_trylock(&mm->mmap_sem)) {
+		/*
+		 * Activate page so shrink_inactive_list is unlikely to unmap
+		 * its ptes while lock is dropped, so swapoff can make progress.
+		 */
+		activate_page(page);
+		unlock_page(page);
+		down_read(&mm->mmap_sem);
+		lock_page(page);
+	}
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
+			break;
+	}
+	up_read(&mm->mmap_sem);
+	return (ret < 0)? ret: 0;
+}
+
+/*
+ * Scan swap_map from current position to next entry still in use.
+ * Recycle to start on reaching the end, returning 0 when empty.
+ */
+static unsigned int find_next_to_unuse(struct swap_info_struct *si,
+					unsigned int prev)
+{
+	unsigned int max = si->max;
+	unsigned int i = prev;
+	unsigned char count;
+
+	/*
+	 * No need for swap_lock here: we're just looking
+	 * for whether an entry is in use, not modifying it; false
+	 * hits are okay, and sys_swapoff() has already prevented new
+	 * allocations from this area (while holding swap_lock).
+	 */
+	for (;;) {
+		if (++i >= max) {
+			if (!prev) {
+				i = 0;
+				break;
+			}
+			/*
+			 * No entries in use at top of swap_map,
+			 * loop back to start and recheck there.
+			 */
+			max = prev + 1;
+			prev = 0;
+			i = 1;
+		}
+		count = si->swap_map[i];
+		if (count && swap_count(count) != SWAP_MAP_BAD)
+			break;
+	}
+	return i;
+}
+
+/*
+ * We completely avoid races by reading each swap page in advance,
+ * and then search for the process using it.  All the necessary
+ * page table adjustments can then be made atomically.
+ */
+static int try_to_unuse(unsigned int type)
+{
+	struct swap_info_struct *si = swap_info[type];
+	struct mm_struct *start_mm;
+	unsigned char *swap_map;
+	unsigned char swcount;
+	struct page *page;
+	swp_entry_t entry;
+	unsigned int i = 0;
+	int retval = 0;
+
+	/*
+	 * When searching mms for an entry, a good strategy is to
+	 * start at the first mm we freed the previous entry from
+	 * (though actually we don't notice whether we or coincidence
+	 * freed the entry).  Initialize this start_mm with a hold.
+	 *
+	 * A simpler strategy would be to start at the last mm we
+	 * freed the previous entry from; but that would take less
+	 * advantage of mmlist ordering, which clusters forked mms
+	 * together, child after parent.  If we race with dup_mmap(), we
+	 * prefer to resolve parent before child, lest we miss entries
+	 * duplicated after we scanned child: using last mm would invert
+	 * that.
+	 */
+	start_mm = &init_mm;
+	atomic_inc(&init_mm.mm_users);
+
+	/*
+	 * Keep on scanning until all entries have gone.  Usually,
+	 * one pass through swap_map is enough, but not necessarily:
+	 * there are races when an instance of an entry might be missed.
+	 */
+	while ((i = find_next_to_unuse(si, i)) != 0) {
+		if (signal_pending(current)) {
+			retval = -EINTR;
+			break;
+		}
+
+		/*
+		 * Get a page for the entry, using the existing swap
+		 * cache page if there is one.  Otherwise, get a clean
+		 * page and read the swap into it.
+		 */
+		swap_map = &si->swap_map[i];
+		entry = swp_entry(type, i);
+		page = read_swap_cache_async(entry,
+					GFP_HIGHUSER_MOVABLE, NULL, 0);
+		if (!page) {
+			/*
+			 * Either swap_duplicate() failed because entry
+			 * has been freed independently, and will not be
+			 * reused since sys_swapoff() already disabled
+			 * allocation from here, or alloc_page() failed.
+			 */
+			if (!*swap_map)
+				continue;
+			retval = -ENOMEM;
+			break;
+		}
+
+		/*
+		 * Don't hold on to start_mm if it looks like exiting.
+		 */
+		if (atomic_read(&start_mm->mm_users) == 1) {
+			mmput(start_mm);
+			start_mm = &init_mm;
+			atomic_inc(&init_mm.mm_users);
+		}
+
+		/*
+		 * Wait for and lock page.  When do_swap_page races with
+		 * try_to_unuse, do_swap_page can handle the fault much
+		 * faster than try_to_unuse can locate the entry.  This
+		 * apparently redundant "wait_on_page_locked" lets try_to_unuse
+		 * defer to do_swap_page in such a case - in some tests,
+		 * do_swap_page and try_to_unuse repeatedly compete.
+		 */
+		wait_on_page_locked(page);
+		wait_on_page_writeback(page);
+		lock_page(page);
+		wait_on_page_writeback(page);
+
+		/*
+		 * Remove all references to entry.
+		 */
+		swcount = *swap_map;
+		if (swap_count(swcount) == SWAP_MAP_SHMEM) {
+			retval = shmem_unuse(entry, page);
+			/* page has already been unlocked and released */
+			if (retval < 0)
+				break;
+			continue;
+		}
+		if (swap_count(swcount) && start_mm != &init_mm)
+			retval = unuse_mm(start_mm, entry, page);
+
+		if (swap_count(*swap_map)) {
+			int set_start_mm = (*swap_map >= swcount);
+			struct list_head *p = &start_mm->mmlist;
+			struct mm_struct *new_start_mm = start_mm;
+			struct mm_struct *prev_mm = start_mm;
+			struct mm_struct *mm;
+
+			atomic_inc(&new_start_mm->mm_users);
+			atomic_inc(&prev_mm->mm_users);
+			spin_lock(&mmlist_lock);
+			while (swap_count(*swap_map) && !retval &&
+					(p = p->next) != &start_mm->mmlist) {
+				mm = list_entry(p, struct mm_struct, mmlist);
+				if (!atomic_inc_not_zero(&mm->mm_users))
+					continue;
+				spin_unlock(&mmlist_lock);
+				mmput(prev_mm);
+				prev_mm = mm;
+
+				cond_resched();
+
+				swcount = *swap_map;
+				if (!swap_count(swcount)) /* any usage ? */
+					;
+				else if (mm == &init_mm)
+					set_start_mm = 1;
+				else
+					retval = unuse_mm(mm, entry, page);
+
+				if (set_start_mm && *swap_map < swcount) {
+					mmput(new_start_mm);
+					atomic_inc(&mm->mm_users);
+					new_start_mm = mm;
+					set_start_mm = 0;
+				}
+				spin_lock(&mmlist_lock);
+			}
+			spin_unlock(&mmlist_lock);
+			mmput(prev_mm);
+			mmput(start_mm);
+			start_mm = new_start_mm;
+		}
+		if (retval) {
+			unlock_page(page);
+			page_cache_release(page);
+			break;
+		}
+
+		/*
+		 * If a reference remains (rare), we would like to leave
+		 * the page in the swap cache; but try_to_unmap could
+		 * then re-duplicate the entry once we drop page lock,
+		 * so we might loop indefinitely; also, that page could
+		 * not be swapped out to other storage meanwhile.  So:
+		 * delete from cache even if there's another reference,
+		 * after ensuring that the data has been saved to disk -
+		 * since if the reference remains (rarer), it will be
+		 * read from disk into another page.  Splitting into two
+		 * pages would be incorrect if swap supported "shared
+		 * private" pages, but they are handled by tmpfs files.
+		 *
+		 * Given how unuse_vma() targets one particular offset
+		 * in an anon_vma, once the anon_vma has been determined,
+		 * this splitting happens to be just what is needed to
+		 * handle where KSM pages have been swapped out: re-reading
+		 * is unnecessarily slow, but we can fix that later on.
+		 */
+		if (swap_count(*swap_map) &&
+		     PageDirty(page) && PageSwapCache(page)) {
+			struct writeback_control wbc = {
+				.sync_mode = WB_SYNC_NONE,
+			};
+
+			swap_writepage(page, &wbc);
+			lock_page(page);
+			wait_on_page_writeback(page);
+		}
+
+		/*
+		 * It is conceivable that a racing task removed this page from
+		 * swap cache just before we acquired the page lock at the top,
+		 * or while we dropped it in unuse_mm().  The page might even
+		 * be back in swap cache on another swap area: that we must not
+		 * delete, since it may not have been written out to swap yet.
+		 */
+		if (PageSwapCache(page) &&
+		    likely(page_private(page) == entry.val))
+			delete_from_swap_cache(page);
+
+		/*
+		 * So we could skip searching mms once swap count went
+		 * to 1, we did not mark any present ptes as dirty: must
+		 * mark page dirty so shrink_page_list will preserve it.
+		 */
+		SetPageDirty(page);
+		unlock_page(page);
+		page_cache_release(page);
+
+		/*
+		 * Make sure that we aren't completely killing
+		 * interactive performance.
+		 */
+		cond_resched();
+	}
+
+	mmput(start_mm);
+	return retval;
+}
+
+/*
+ * After a successful try_to_unuse, if no swap is now in use, we know
+ * we can empty the mmlist.  swap_lock must be held on entry and exit.
+ * Note that mmlist_lock nests inside swap_lock, and an mm must be
+ * added to the mmlist just after page_duplicate - before would be racy.
+ */
+static void drain_mmlist(void)
+{
+	struct list_head *p, *next;
+	unsigned int type;
+
+	for (type = 0; type < nr_swapfiles; type++)
+		if (swap_info[type]->inuse_pages)
+			return;
+	spin_lock(&mmlist_lock);
+	list_for_each_safe(p, next, &init_mm.mmlist)
+		list_del_init(p);
+	spin_unlock(&mmlist_lock);
+}
+
+/*
+ * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
+ * corresponds to page offset for the specified swap entry.
+ * Note that the type of this function is sector_t, but it returns page offset
+ * into the bdev, not sector offset.
+ */
+static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
+{
+	struct swap_info_struct *sis;
+	struct swap_extent *start_se;
+	struct swap_extent *se;
+	pgoff_t offset;
+
+	sis = swap_info[swp_type(entry)];
+	*bdev = sis->bdev;
+
+	offset = swp_offset(entry);
+	start_se = sis->curr_swap_extent;
+	se = start_se;
+
+	for ( ; ; ) {
+		struct list_head *lh;
+
+		if (se->start_page <= offset &&
+				offset < (se->start_page + se->nr_pages)) {
+			return se->start_block + (offset - se->start_page);
+		}
+		lh = se->list.next;
+		se = list_entry(lh, struct swap_extent, list);
+		sis->curr_swap_extent = se;
+		BUG_ON(se == start_se);		/* It *must* be present */
+	}
+}
+
+/*
+ * Returns the page offset into bdev for the specified page's swap entry.
+ */
+sector_t map_swap_page(struct page *page, struct block_device **bdev)
+{
+	swp_entry_t entry;
+	entry.val = page_private(page);
+	return map_swap_entry(entry, bdev);
+}
+
+/*
+ * Free all of a swapdev's extent information
+ */
+static void destroy_swap_extents(struct swap_info_struct *sis)
+{
+	while (!list_empty(&sis->first_swap_extent.list)) {
+		struct swap_extent *se;
+
+		se = list_entry(sis->first_swap_extent.list.next,
+				struct swap_extent, list);
+		list_del(&se->list);
+		kfree(se);
+	}
+}
+
+/*
+ * Add a block range (and the corresponding page range) into this swapdev's
+ * extent list.  The extent list is kept sorted in page order.
+ *
+ * This function rather assumes that it is called in ascending page order.
+ */
+static int
+add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
+		unsigned long nr_pages, sector_t start_block)
+{
+	struct swap_extent *se;
+	struct swap_extent *new_se;
+	struct list_head *lh;
+
+	if (start_page == 0) {
+		se = &sis->first_swap_extent;
+		sis->curr_swap_extent = se;
+		se->start_page = 0;
+		se->nr_pages = nr_pages;
+		se->start_block = start_block;
+		return 1;
+	} else {
+		lh = sis->first_swap_extent.list.prev;	/* Highest extent */
+		se = list_entry(lh, struct swap_extent, list);
+		BUG_ON(se->start_page + se->nr_pages != start_page);
+		if (se->start_block + se->nr_pages == start_block) {
+			/* Merge it */
+			se->nr_pages += nr_pages;
+			return 0;
+		}
+	}
+
+	/*
+	 * No merge.  Insert a new extent, preserving ordering.
+	 */
+	new_se = kmalloc(sizeof(*se), GFP_KERNEL);
+	if (new_se == NULL)
+		return -ENOMEM;
+	new_se->start_page = start_page;
+	new_se->nr_pages = nr_pages;
+	new_se->start_block = start_block;
+
+	list_add_tail(&new_se->list, &sis->first_swap_extent.list);
+	return 1;
+}
+
+/*
+ * A `swap extent' is a simple thing which maps a contiguous range of pages
+ * onto a contiguous range of disk blocks.  An ordered list of swap extents
+ * is built at swapon time and is then used at swap_writepage/swap_readpage
+ * time for locating where on disk a page belongs.
+ *
+ * If the swapfile is an S_ISBLK block device, a single extent is installed.
+ * This is done so that the main operating code can treat S_ISBLK and S_ISREG
+ * swap files identically.
+ *
+ * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
+ * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
+ * swapfiles are handled *identically* after swapon time.
+ *
+ * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
+ * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
+ * some stray blocks are found which do not fall within the PAGE_SIZE alignment
+ * requirements, they are simply tossed out - we will never use those blocks
+ * for swapping.
+ *
+ * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
+ * prevents root from shooting her foot off by ftruncating an in-use swapfile,
+ * which will scribble on the fs.
+ *
+ * The amount of disk space which a single swap extent represents varies.
+ * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
+ * extents in the list.  To avoid much list walking, we cache the previous
+ * search location in `curr_swap_extent', and start new searches from there.
+ * This is extremely effective.  The average number of iterations in
+ * map_swap_page() has been measured at about 0.3 per page.  - akpm.
+ */
+static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
+{
+	struct inode *inode;
+	unsigned blocks_per_page;
+	unsigned long page_no;
+	unsigned blkbits;
+	sector_t probe_block;
+	sector_t last_block;
+	sector_t lowest_block = -1;
+	sector_t highest_block = 0;
+	int nr_extents = 0;
+	int ret;
+
+	inode = sis->swap_file->f_mapping->host;
+	if (S_ISBLK(inode->i_mode)) {
+		ret = add_swap_extent(sis, 0, sis->max, 0);
+		*span = sis->pages;
+		goto out;
+	}
+
+	blkbits = inode->i_blkbits;
+	blocks_per_page = PAGE_SIZE >> blkbits;
+
+	/*
+	 * Map all the blocks into the extent list.  This code doesn't try
+	 * to be very smart.
+	 */
+	probe_block = 0;
+	page_no = 0;
+	last_block = i_size_read(inode) >> blkbits;
+	while ((probe_block + blocks_per_page) <= last_block &&
+			page_no < sis->max) {
+		unsigned block_in_page;
+		sector_t first_block;
+
+		first_block = bmap(inode, probe_block);
+		if (first_block == 0)
+			goto bad_bmap;
+
+		/*
+		 * It must be PAGE_SIZE aligned on-disk
+		 */
+		if (first_block & (blocks_per_page - 1)) {
+			probe_block++;
+			goto reprobe;
+		}
+
+		for (block_in_page = 1; block_in_page < blocks_per_page;
+					block_in_page++) {
+			sector_t block;
+
+			block = bmap(inode, probe_block + block_in_page);
+			if (block == 0)
+				goto bad_bmap;
+			if (block != first_block + block_in_page) {
+				/* Discontiguity */
+				probe_block++;
+				goto reprobe;
+			}
+		}
+
+		first_block >>= (PAGE_SHIFT - blkbits);
+		if (page_no) {	/* exclude the header page */
+			if (first_block < lowest_block)
+				lowest_block = first_block;
+			if (first_block > highest_block)
+				highest_block = first_block;
+		}
+
+		/*
+		 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
+		 */
+		ret = add_swap_extent(sis, page_no, 1, first_block);
+		if (ret < 0)
+			goto out;
+		nr_extents += ret;
+		page_no++;
+		probe_block += blocks_per_page;
+reprobe:
+		continue;
+	}
+	ret = nr_extents;
+	*span = 1 + highest_block - lowest_block;
+	if (page_no == 0)
+		page_no = 1;	/* force Empty message */
+	sis->max = page_no;
+	sis->pages = page_no - 1;
+	sis->highest_bit = page_no - 1;
+out:
+	return ret;
+bad_bmap:
+	printk(KERN_ERR "swapon: swapfile has holes\n");
+	ret = -EINVAL;
+	goto out;
+}
+
+SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
+{
+	struct swap_info_struct *p = NULL;
+	unsigned char *swap_map;
+	struct file *swap_file, *victim;
+	struct address_space *mapping;
+	struct inode *inode;
+	char *pathname;
+	int i, type, prev;
+	int err;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	pathname = getname(specialfile);
+	err = PTR_ERR(pathname);
+	if (IS_ERR(pathname))
+		goto out;
+
+	victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
+	putname(pathname);
+	err = PTR_ERR(victim);
+	if (IS_ERR(victim))
+		goto out;
+
+	mapping = victim->f_mapping;
+	prev = -1;
+	spin_lock(&swap_lock);
+	for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
+		p = swap_info[type];
+		if (p->flags & SWP_WRITEOK) {
+			if (p->swap_file->f_mapping == mapping)
+				break;
+		}
+		prev = type;
+	}
+	if (type < 0) {
+		err = -EINVAL;
+		spin_unlock(&swap_lock);
+		goto out_dput;
+	}
+	if (!security_vm_enough_memory(p->pages))
+		vm_unacct_memory(p->pages);
+	else {
+		err = -ENOMEM;
+		spin_unlock(&swap_lock);
+		goto out_dput;
+	}
+	if (prev < 0)
+		swap_list.head = p->next;
+	else
+		swap_info[prev]->next = p->next;
+	if (type == swap_list.next) {
+		/* just pick something that's safe... */
+		swap_list.next = swap_list.head;
+	}
+	if (p->prio < 0) {
+		for (i = p->next; i >= 0; i = swap_info[i]->next)
+			swap_info[i]->prio = p->prio--;
+		least_priority++;
+	}
+	nr_swap_pages -= p->pages;
+	total_swap_pages -= p->pages;
+	p->flags &= ~SWP_WRITEOK;
+	spin_unlock(&swap_lock);
+
+	current->flags |= PF_OOM_ORIGIN;
+	err = try_to_unuse(type);
+	current->flags &= ~PF_OOM_ORIGIN;
+
+	if (err) {
+		/* re-insert swap space back into swap_list */
+		spin_lock(&swap_lock);
+		if (p->prio < 0)
+			p->prio = --least_priority;
+		prev = -1;
+		for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+			if (p->prio >= swap_info[i]->prio)
+				break;
+			prev = i;
+		}
+		p->next = i;
+		if (prev < 0)
+			swap_list.head = swap_list.next = type;
+		else
+			swap_info[prev]->next = type;
+		nr_swap_pages += p->pages;
+		total_swap_pages += p->pages;
+		p->flags |= SWP_WRITEOK;
+		spin_unlock(&swap_lock);
+		goto out_dput;
+	}
+
+	/* wait for any unplug function to finish */
+	down_write(&swap_unplug_sem);
+	up_write(&swap_unplug_sem);
+
+	destroy_swap_extents(p);
+	if (p->flags & SWP_CONTINUED)
+		free_swap_count_continuations(p);
+
+	mutex_lock(&swapon_mutex);
+	spin_lock(&swap_lock);
+	drain_mmlist();
+
+	/* wait for anyone still in scan_swap_map */
+	p->highest_bit = 0;		/* cuts scans short */
+	while (p->flags >= SWP_SCANNING) {
+		spin_unlock(&swap_lock);
+		schedule_timeout_uninterruptible(1);
+		spin_lock(&swap_lock);
+	}
+
+	swap_file = p->swap_file;
+	p->swap_file = NULL;
+	p->max = 0;
+	swap_map = p->swap_map;
+	p->swap_map = NULL;
+	p->flags = 0;
+	spin_unlock(&swap_lock);
+	mutex_unlock(&swapon_mutex);
+	vfree(swap_map);
+	/* Destroy swap account informatin */
+	swap_cgroup_swapoff(type);
+
+	inode = mapping->host;
+	if (S_ISBLK(inode->i_mode)) {
+		struct block_device *bdev = I_BDEV(inode);
+		set_blocksize(bdev, p->old_block_size);
+		bd_release(bdev);
+	} else {
+		mutex_lock(&inode->i_mutex);
+		inode->i_flags &= ~S_SWAPFILE;
+		mutex_unlock(&inode->i_mutex);
+	}
+	filp_close(swap_file, NULL);
+	err = 0;
+
+out_dput:
+	filp_close(victim, NULL);
+out:
+	return err;
+}
+
+#ifdef CONFIG_PROC_FS
+/* iterator */
+static void *swap_start(struct seq_file *swap, loff_t *pos)
+{
+	struct swap_info_struct *si;
+	int type;
+	loff_t l = *pos;
+
+	mutex_lock(&swapon_mutex);
+
+	if (!l)
+		return SEQ_START_TOKEN;
+
+	for (type = 0; type < nr_swapfiles; type++) {
+		smp_rmb();	/* read nr_swapfiles before swap_info[type] */
+		si = swap_info[type];
+		if (!(si->flags & SWP_USED) || !si->swap_map)
+			continue;
+		if (!--l)
+			return si;
+	}
+
+	return NULL;
+}
+
+static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
+{
+	struct swap_info_struct *si = v;
+	int type;
+
+	if (v == SEQ_START_TOKEN)
+		type = 0;
+	else
+		type = si->type + 1;
+
+	for (; type < nr_swapfiles; type++) {
+		smp_rmb();	/* read nr_swapfiles before swap_info[type] */
+		si = swap_info[type];
+		if (!(si->flags & SWP_USED) || !si->swap_map)
+			continue;
+		++*pos;
+		return si;
+	}
+
+	return NULL;
+}
+
+static void swap_stop(struct seq_file *swap, void *v)
+{
+	mutex_unlock(&swapon_mutex);
+}
+
+static int swap_show(struct seq_file *swap, void *v)
+{
+	struct swap_info_struct *si = v;
+	struct file *file;
+	int len;
+
+	if (si == SEQ_START_TOKEN) {
+		seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
+		return 0;
+	}
+
+	file = si->swap_file;
+	len = seq_path(swap, &file->f_path, " \t\n\\");
+	seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
+			len < 40 ? 40 - len : 1, " ",
+			S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
+				"partition" : "file\t",
+			si->pages << (PAGE_SHIFT - 10),
+			si->inuse_pages << (PAGE_SHIFT - 10),
+			si->prio);
+	return 0;
+}
+
+static const struct seq_operations swaps_op = {
+	.start =	swap_start,
+	.next =		swap_next,
+	.stop =		swap_stop,
+	.show =		swap_show
+};
+
+static int swaps_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &swaps_op);
+}
+
+static const struct file_operations proc_swaps_operations = {
+	.open		= swaps_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static int __init procswaps_init(void)
+{
+	proc_create("swaps", 0, NULL, &proc_swaps_operations);
+	return 0;
+}
+__initcall(procswaps_init);
+#endif /* CONFIG_PROC_FS */
+
+#ifdef MAX_SWAPFILES_CHECK
+static int __init max_swapfiles_check(void)
+{
+	MAX_SWAPFILES_CHECK();
+	return 0;
+}
+late_initcall(max_swapfiles_check);
+#endif
+
+/*
+ * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
+ *
+ * The swapon system call
+ */
+SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
+{
+	struct swap_info_struct *p;
+	char *name = NULL;
+	struct block_device *bdev = NULL;
+	struct file *swap_file = NULL;
+	struct address_space *mapping;
+	unsigned int type;
+	int i, prev;
+	int error;
+	union swap_header *swap_header;
+	unsigned int nr_good_pages;
+	int nr_extents = 0;
+	sector_t span;
+	unsigned long maxpages;
+	unsigned long swapfilepages;
+	unsigned char *swap_map = NULL;
+	struct page *page = NULL;
+	struct inode *inode = NULL;
+	int did_down = 0;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return -ENOMEM;
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		if (!(swap_info[type]->flags & SWP_USED))
+			break;
+	}
+	error = -EPERM;
+	if (type >= MAX_SWAPFILES) {
+		spin_unlock(&swap_lock);
+		kfree(p);
+		goto out;
+	}
+	if (type >= nr_swapfiles) {
+		p->type = type;
+		swap_info[type] = p;
+		/*
+		 * Write swap_info[type] before nr_swapfiles, in case a
+		 * racing procfs swap_start() or swap_next() is reading them.
+		 * (We never shrink nr_swapfiles, we never free this entry.)
+		 */
+		smp_wmb();
+		nr_swapfiles++;
+	} else {
+		kfree(p);
+		p = swap_info[type];
+		/*
+		 * Do not memset this entry: a racing procfs swap_next()
+		 * would be relying on p->type to remain valid.
+		 */
+	}
+	INIT_LIST_HEAD(&p->first_swap_extent.list);
+	p->flags = SWP_USED;
+	p->next = -1;
+	spin_unlock(&swap_lock);
+
+	name = getname(specialfile);
+	error = PTR_ERR(name);
+	if (IS_ERR(name)) {
+		name = NULL;
+		goto bad_swap_2;
+	}
+	swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
+	error = PTR_ERR(swap_file);
+	if (IS_ERR(swap_file)) {
+		swap_file = NULL;
+		goto bad_swap_2;
+	}
+
+	p->swap_file = swap_file;
+	mapping = swap_file->f_mapping;
+	inode = mapping->host;
+
+	error = -EBUSY;
+	for (i = 0; i < nr_swapfiles; i++) {
+		struct swap_info_struct *q = swap_info[i];
+
+		if (i == type || !q->swap_file)
+			continue;
+		if (mapping == q->swap_file->f_mapping)
+			goto bad_swap;
+	}
+
+	error = -EINVAL;
+	if (S_ISBLK(inode->i_mode)) {
+		bdev = I_BDEV(inode);
+		error = bd_claim(bdev, sys_swapon);
+		if (error < 0) {
+			bdev = NULL;
+			error = -EINVAL;
+			goto bad_swap;
+		}
+		p->old_block_size = block_size(bdev);
+		error = set_blocksize(bdev, PAGE_SIZE);
+		if (error < 0)
+			goto bad_swap;
+		p->bdev = bdev;
+		p->flags |= SWP_BLKDEV;
+	} else if (S_ISREG(inode->i_mode)) {
+		p->bdev = inode->i_sb->s_bdev;
+		mutex_lock(&inode->i_mutex);
+		did_down = 1;
+		if (IS_SWAPFILE(inode)) {
+			error = -EBUSY;
+			goto bad_swap;
+		}
+	} else {
+		goto bad_swap;
+	}
+
+	swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
+
+	/*
+	 * Read the swap header.
+	 */
+	if (!mapping->a_ops->readpage) {
+		error = -EINVAL;
+		goto bad_swap;
+	}
+	page = read_mapping_page(mapping, 0, swap_file);
+	if (IS_ERR(page)) {
+		error = PTR_ERR(page);
+		goto bad_swap;
+	}
+	swap_header = kmap(page);
+
+	if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
+		printk(KERN_ERR "Unable to find swap-space signature\n");
+		error = -EINVAL;
+		goto bad_swap;
+	}
+
+	/* swap partition endianess hack... */
+	if (swab32(swap_header->info.version) == 1) {
+		swab32s(&swap_header->info.version);
+		swab32s(&swap_header->info.last_page);
+		swab32s(&swap_header->info.nr_badpages);
+		for (i = 0; i < swap_header->info.nr_badpages; i++)
+			swab32s(&swap_header->info.badpages[i]);
+	}
+	/* Check the swap header's sub-version */
+	if (swap_header->info.version != 1) {
+		printk(KERN_WARNING
+		       "Unable to handle swap header version %d\n",
+		       swap_header->info.version);
+		error = -EINVAL;
+		goto bad_swap;
+	}
+
+	p->lowest_bit  = 1;
+	p->cluster_next = 1;
+	p->cluster_nr = 0;
+
+	/*
+	 * Find out how many pages are allowed for a single swap
+	 * device. There are two limiting factors: 1) the number of
+	 * bits for the swap offset in the swp_entry_t type and
+	 * 2) the number of bits in the a swap pte as defined by
+	 * the different architectures. In order to find the
+	 * largest possible bit mask a swap entry with swap type 0
+	 * and swap offset ~0UL is created, encoded to a swap pte,
+	 * decoded to a swp_entry_t again and finally the swap
+	 * offset is extracted. This will mask all the bits from
+	 * the initial ~0UL mask that can't be encoded in either
+	 * the swp_entry_t or the architecture definition of a
+	 * swap pte.
+	 */
+	maxpages = swp_offset(pte_to_swp_entry(
+			swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
+	if (maxpages > swap_header->info.last_page) {
+		maxpages = swap_header->info.last_page + 1;
+		/* p->max is an unsigned int: don't overflow it */
+		if ((unsigned int)maxpages == 0)
+			maxpages = UINT_MAX;
+	}
+	p->highest_bit = maxpages - 1;
+
+	error = -EINVAL;
+	if (!maxpages)
+		goto bad_swap;
+	if (swapfilepages && maxpages > swapfilepages) {
+		printk(KERN_WARNING
+		       "Swap area shorter than signature indicates\n");
+		goto bad_swap;
+	}
+	if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
+		goto bad_swap;
+	if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+		goto bad_swap;
+
+	/* OK, set up the swap map and apply the bad block list */
+	swap_map = vmalloc(maxpages);
+	if (!swap_map) {
+		error = -ENOMEM;
+		goto bad_swap;
+	}
+
+	memset(swap_map, 0, maxpages);
+	nr_good_pages = maxpages - 1;	/* omit header page */
+
+	for (i = 0; i < swap_header->info.nr_badpages; i++) {
+		unsigned int page_nr = swap_header->info.badpages[i];
+		if (page_nr == 0 || page_nr > swap_header->info.last_page) {
+			error = -EINVAL;
+			goto bad_swap;
+		}
+		if (page_nr < maxpages) {
+			swap_map[page_nr] = SWAP_MAP_BAD;
+			nr_good_pages--;
+		}
+	}
+
+	error = swap_cgroup_swapon(type, maxpages);
+	if (error)
+		goto bad_swap;
+
+	if (nr_good_pages) {
+		swap_map[0] = SWAP_MAP_BAD;
+		p->max = maxpages;
+		p->pages = nr_good_pages;
+		nr_extents = setup_swap_extents(p, &span);
+		if (nr_extents < 0) {
+			error = nr_extents;
+			goto bad_swap;
+		}
+		nr_good_pages = p->pages;
+	}
+	if (!nr_good_pages) {
+		printk(KERN_WARNING "Empty swap-file\n");
+		error = -EINVAL;
+		goto bad_swap;
+	}
+
+	if (p->bdev) {
+		if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
+			p->flags |= SWP_SOLIDSTATE;
+			p->cluster_next = 1 + (random32() % p->highest_bit);
+		}
+		if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
+			p->flags |= SWP_DISCARDABLE;
+	}
+
+	mutex_lock(&swapon_mutex);
+	spin_lock(&swap_lock);
+	if (swap_flags & SWAP_FLAG_PREFER)
+		p->prio =
+		  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
+	else
+		p->prio = --least_priority;
+	p->swap_map = swap_map;
+	p->flags |= SWP_WRITEOK;
+	nr_swap_pages += nr_good_pages;
+	total_swap_pages += nr_good_pages;
+
+	printk(KERN_INFO "Adding %uk swap on %s.  "
+			"Priority:%d extents:%d across:%lluk %s%s\n",
+		nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
+		nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
+		(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
+		(p->flags & SWP_DISCARDABLE) ? "D" : "");
+
+	/* insert swap space into swap_list: */
+	prev = -1;
+	for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+		if (p->prio >= swap_info[i]->prio)
+			break;
+		prev = i;
+	}
+	p->next = i;
+	if (prev < 0)
+		swap_list.head = swap_list.next = type;
+	else
+		swap_info[prev]->next = type;
+	spin_unlock(&swap_lock);
+	mutex_unlock(&swapon_mutex);
+	error = 0;
+	goto out;
+bad_swap:
+	if (bdev) {
+		set_blocksize(bdev, p->old_block_size);
+		bd_release(bdev);
+	}
+	destroy_swap_extents(p);
+	swap_cgroup_swapoff(type);
+bad_swap_2:
+	spin_lock(&swap_lock);
+	p->swap_file = NULL;
+	p->flags = 0;
+	spin_unlock(&swap_lock);
+	vfree(swap_map);
+	if (swap_file)
+		filp_close(swap_file, NULL);
+out:
+	if (page && !IS_ERR(page)) {
+		kunmap(page);
+		page_cache_release(page);
+	}
+	if (name)
+		putname(name);
+	if (did_down) {
+		if (!error)
+			inode->i_flags |= S_SWAPFILE;
+		mutex_unlock(&inode->i_mutex);
+	}
+	return error;
+}
+
+void si_swapinfo(struct sysinfo *val)
+{
+	unsigned int type;
+	unsigned long nr_to_be_unused = 0;
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *si = swap_info[type];
+
+		if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
+			nr_to_be_unused += si->inuse_pages;
+	}
+	val->freeswap = nr_swap_pages + nr_to_be_unused;
+	val->totalswap = total_swap_pages + nr_to_be_unused;
+	spin_unlock(&swap_lock);
+}
+
+/*
+ * Verify that a swap entry is valid and increment its swap map count.
+ *
+ * Returns error code in following case.
+ * - success -> 0
+ * - swp_entry is invalid -> EINVAL
+ * - swp_entry is migration entry -> EINVAL
+ * - swap-cache reference is requested but there is already one. -> EEXIST
+ * - swap-cache reference is requested but the entry is not used. -> ENOENT
+ * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
+ */
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
+{
+	struct swap_info_struct *p;
+	unsigned long offset, type;
+	unsigned char count;
+	unsigned char has_cache;
+	int err = -EINVAL;
+
+	if (non_swap_entry(entry))
+		goto out;
+
+	type = swp_type(entry);
+	if (type >= nr_swapfiles)
+		goto bad_file;
+	p = swap_info[type];
+	offset = swp_offset(entry);
+
+	spin_lock(&swap_lock);
+	if (unlikely(offset >= p->max))
+		goto unlock_out;
+
+	count = p->swap_map[offset];
+	has_cache = count & SWAP_HAS_CACHE;
+	count &= ~SWAP_HAS_CACHE;
+	err = 0;
+
+	if (usage == SWAP_HAS_CACHE) {
+
+		/* set SWAP_HAS_CACHE if there is no cache and entry is used */
+		if (!has_cache && count)
+			has_cache = SWAP_HAS_CACHE;
+		else if (has_cache)		/* someone else added cache */
+			err = -EEXIST;
+		else				/* no users remaining */
+			err = -ENOENT;
+
+	} else if (count || has_cache) {
+
+		if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
+			count += usage;
+		else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
+			err = -EINVAL;
+		else if (swap_count_continued(p, offset, count))
+			count = COUNT_CONTINUED;
+		else
+			err = -ENOMEM;
+	} else
+		err = -ENOENT;			/* unused swap entry */
+
+	p->swap_map[offset] = count | has_cache;
+
+unlock_out:
+	spin_unlock(&swap_lock);
+out:
+	return err;
+
+bad_file:
+	printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
+	goto out;
+}
+
+/*
+ * Help swapoff by noting that swap entry belongs to shmem/tmpfs
+ * (in which case its reference count is never incremented).
+ */
+void swap_shmem_alloc(swp_entry_t entry)
+{
+	__swap_duplicate(entry, SWAP_MAP_SHMEM);
+}
+
+/*
+ * Increase reference count of swap entry by 1.
+ * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
+ * but could not be atomically allocated.  Returns 0, just as if it succeeded,
+ * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
+ * might occur if a page table entry has got corrupted.
+ */
+int swap_duplicate(swp_entry_t entry)
+{
+	int err = 0;
+
+	while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
+		err = add_swap_count_continuation(entry, GFP_ATOMIC);
+	return err;
+}
+
+/*
+ * @entry: swap entry for which we allocate swap cache.
+ *
+ * Called when allocating swap cache for existing swap entry,
+ * This can return error codes. Returns 0 at success.
+ * -EBUSY means there is a swap cache.
+ * Note: return code is different from swap_duplicate().
+ */
+int swapcache_prepare(swp_entry_t entry)
+{
+	return __swap_duplicate(entry, SWAP_HAS_CACHE);
+}
+
+/*
+ * swap_lock prevents swap_map being freed. Don't grab an extra
+ * reference on the swaphandle, it doesn't matter if it becomes unused.
+ */
+int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
+{
+	struct swap_info_struct *si;
+	int our_page_cluster = page_cluster;
+	pgoff_t target, toff;
+	pgoff_t base, end;
+	int nr_pages = 0;
+
+	if (!our_page_cluster)	/* no readahead */
+		return 0;
+
+	si = swap_info[swp_type(entry)];
+	target = swp_offset(entry);
+	base = (target >> our_page_cluster) << our_page_cluster;
+	end = base + (1 << our_page_cluster);
+	if (!base)		/* first page is swap header */
+		base++;
+
+	spin_lock(&swap_lock);
+	if (end > si->max)	/* don't go beyond end of map */
+		end = si->max;
+
+	/* Count contiguous allocated slots above our target */
+	for (toff = target; ++toff < end; nr_pages++) {
+		/* Don't read in free or bad pages */
+		if (!si->swap_map[toff])
+			break;
+		if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
+			break;
+	}
+	/* Count contiguous allocated slots below our target */
+	for (toff = target; --toff >= base; nr_pages++) {
+		/* Don't read in free or bad pages */
+		if (!si->swap_map[toff])
+			break;
+		if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
+			break;
+	}
+	spin_unlock(&swap_lock);
+
+	/*
+	 * Indicate starting offset, and return number of pages to get:
+	 * if only 1, say 0, since there's then no readahead to be done.
+	 */
+	*offset = ++toff;
+	return nr_pages? ++nr_pages: 0;
+}
+
+/*
+ * add_swap_count_continuation - called when a swap count is duplicated
+ * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
+ * page of the original vmalloc'ed swap_map, to hold the continuation count
+ * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
+ * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
+ *
+ * These continuation pages are seldom referenced: the common paths all work
+ * on the original swap_map, only referring to a continuation page when the
+ * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
+ *
+ * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
+ * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
+ * can be called after dropping locks.
+ */
+int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
+{
+	struct swap_info_struct *si;
+	struct page *head;
+	struct page *page;
+	struct page *list_page;
+	pgoff_t offset;
+	unsigned char count;
+
+	/*
+	 * When debugging, it's easier to use __GFP_ZERO here; but it's better
+	 * for latency not to zero a page while GFP_ATOMIC and holding locks.
+	 */
+	page = alloc_page(gfp_mask | __GFP_HIGHMEM);
+
+	si = swap_info_get(entry);
+	if (!si) {
+		/*
+		 * An acceptable race has occurred since the failing
+		 * __swap_duplicate(): the swap entry has been freed,
+		 * perhaps even the whole swap_map cleared for swapoff.
+		 */
+		goto outer;
+	}
+
+	offset = swp_offset(entry);
+	count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
+
+	if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
+		/*
+		 * The higher the swap count, the more likely it is that tasks
+		 * will race to add swap count continuation: we need to avoid
+		 * over-provisioning.
+		 */
+		goto out;
+	}
+
+	if (!page) {
+		spin_unlock(&swap_lock);
+		return -ENOMEM;
+	}
+
+	/*
+	 * We are fortunate that although vmalloc_to_page uses pte_offset_map,
+	 * no architecture is using highmem pages for kernel pagetables: so it
+	 * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
+	 */
+	head = vmalloc_to_page(si->swap_map + offset);
+	offset &= ~PAGE_MASK;
+
+	/*
+	 * Page allocation does not initialize the page's lru field,
+	 * but it does always reset its private field.
+	 */
+	if (!page_private(head)) {
+		BUG_ON(count & COUNT_CONTINUED);
+		INIT_LIST_HEAD(&head->lru);
+		set_page_private(head, SWP_CONTINUED);
+		si->flags |= SWP_CONTINUED;
+	}
+
+	list_for_each_entry(list_page, &head->lru, lru) {
+		unsigned char *map;
+
+		/*
+		 * If the previous map said no continuation, but we've found
+		 * a continuation page, free our allocation and use this one.
+		 */
+		if (!(count & COUNT_CONTINUED))
+			goto out;
+
+		map = kmap_atomic(list_page, KM_USER0) + offset;
+		count = *map;
+		kunmap_atomic(map, KM_USER0);
+
+		/*
+		 * If this continuation count now has some space in it,
+		 * free our allocation and use this one.
+		 */
+		if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
+			goto out;
+	}
+
+	list_add_tail(&page->lru, &head->lru);
+	page = NULL;			/* now it's attached, don't free it */
+out:
+	spin_unlock(&swap_lock);
+outer:
+	if (page)
+		__free_page(page);
+	return 0;
+}
+
+/*
+ * swap_count_continued - when the original swap_map count is incremented
+ * from SWAP_MAP_MAX, check if there is already a continuation page to carry
+ * into, carry if so, or else fail until a new continuation page is allocated;
+ * when the original swap_map count is decremented from 0 with continuation,
+ * borrow from the continuation and report whether it still holds more.
+ * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
+ */
+static bool swap_count_continued(struct swap_info_struct *si,
+				 pgoff_t offset, unsigned char count)
+{
+	struct page *head;
+	struct page *page;
+	unsigned char *map;
+
+	head = vmalloc_to_page(si->swap_map + offset);
+	if (page_private(head) != SWP_CONTINUED) {
+		BUG_ON(count & COUNT_CONTINUED);
+		return false;		/* need to add count continuation */
+	}
+
+	offset &= ~PAGE_MASK;
+	page = list_entry(head->lru.next, struct page, lru);
+	map = kmap_atomic(page, KM_USER0) + offset;
+
+	if (count == SWAP_MAP_MAX)	/* initial increment from swap_map */
+		goto init_map;		/* jump over SWAP_CONT_MAX checks */
+
+	if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
+		/*
+		 * Think of how you add 1 to 999
+		 */
+		while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
+			kunmap_atomic(map, KM_USER0);
+			page = list_entry(page->lru.next, struct page, lru);
+			BUG_ON(page == head);
+			map = kmap_atomic(page, KM_USER0) + offset;
+		}
+		if (*map == SWAP_CONT_MAX) {
+			kunmap_atomic(map, KM_USER0);
+			page = list_entry(page->lru.next, struct page, lru);
+			if (page == head)
+				return false;	/* add count continuation */
+			map = kmap_atomic(page, KM_USER0) + offset;
+init_map:		*map = 0;		/* we didn't zero the page */
+		}
+		*map += 1;
+		kunmap_atomic(map, KM_USER0);
+		page = list_entry(page->lru.prev, struct page, lru);
+		while (page != head) {
+			map = kmap_atomic(page, KM_USER0) + offset;
+			*map = COUNT_CONTINUED;
+			kunmap_atomic(map, KM_USER0);
+			page = list_entry(page->lru.prev, struct page, lru);
+		}
+		return true;			/* incremented */
+
+	} else {				/* decrementing */
+		/*
+		 * Think of how you subtract 1 from 1000
+		 */
+		BUG_ON(count != COUNT_CONTINUED);
+		while (*map == COUNT_CONTINUED) {
+			kunmap_atomic(map, KM_USER0);
+			page = list_entry(page->lru.next, struct page, lru);
+			BUG_ON(page == head);
+			map = kmap_atomic(page, KM_USER0) + offset;
+		}
+		BUG_ON(*map == 0);
+		*map -= 1;
+		if (*map == 0)
+			count = 0;
+		kunmap_atomic(map, KM_USER0);
+		page = list_entry(page->lru.prev, struct page, lru);
+		while (page != head) {
+			map = kmap_atomic(page, KM_USER0) + offset;
+			*map = SWAP_CONT_MAX | count;
+			count = COUNT_CONTINUED;
+			kunmap_atomic(map, KM_USER0);
+			page = list_entry(page->lru.prev, struct page, lru);
+		}
+		return count == COUNT_CONTINUED;
+	}
+}
+
+/*
+ * free_swap_count_continuations - swapoff free all the continuation pages
+ * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
+ */
+static void free_swap_count_continuations(struct swap_info_struct *si)
+{
+	pgoff_t offset;
+
+	for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
+		struct page *head;
+		head = vmalloc_to_page(si->swap_map + offset);
+		if (page_private(head)) {
+			struct list_head *this, *next;
+			list_for_each_safe(this, next, &head->lru) {
+				struct page *page;
+				page = list_entry(this, struct page, lru);
+				list_del(this);
+				__free_page(page);
+			}
+		}
+	}
+}