X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=mm%2Fswapfile.c;h=6c0585b16418661529ef1c0399450bf4b9128a45;hb=6e1415467614e854fee660ff6648bd10fa976e95;hp=ddc6d92be2cb43166acea2456be2a962d6070fa0;hpb=bced0520fe462bb94021dcabd32e99630c171be2;p=safe%2Fjmp%2Flinux-2.6

diff --git a/mm/swapfile.c b/mm/swapfile.c
index ddc6d92..6c0585b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -22,6 +22,7 @@
 #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>
@@ -33,12 +34,17 @@
 #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 swap_overflow;
 static int least_priority;
 
 static const char Bad_file[] = "Bad swap file entry ";
@@ -48,10 +54,41 @@ 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 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
@@ -66,7 +103,7 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
 	down_read(&swap_unplug_sem);
 	entry.val = page_private(page);
 	if (PageSwapCache(page)) {
-		struct block_device *bdev = swap_info[swp_type(entry)].bdev;
+		struct block_device *bdev = swap_info[swp_type(entry)]->bdev;
 		struct backing_dev_info *bdi;
 
 		/*
@@ -92,22 +129,28 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
 static int discard_swap(struct swap_info_struct *si)
 {
 	struct swap_extent *se;
+	sector_t start_block;
+	sector_t nr_blocks;
 	int err = 0;
 
-	list_for_each_entry(se, &si->extent_list, list) {
-		sector_t start_block = se->start_block << (PAGE_SHIFT - 9);
-		sector_t nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
+	/* 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, DISCARD_FL_BARRIER);
+		if (err)
+			return err;
+		cond_resched();
+	}
 
-		if (se->start_page == 0) {
-			/* Do not discard the swap header page! */
-			start_block += 1 << (PAGE_SHIFT - 9);
-			nr_blocks -= 1 << (PAGE_SHIFT - 9);
-			if (!nr_blocks)
-				continue;
-		}
+	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);
+				nr_blocks, GFP_KERNEL, DISCARD_FL_BARRIER);
 		if (err)
 			break;
 
@@ -146,13 +189,11 @@ static void discard_swap_cluster(struct swap_info_struct *si,
 			start_block <<= PAGE_SHIFT - 9;
 			nr_blocks <<= PAGE_SHIFT - 9;
 			if (blkdev_issue_discard(si->bdev, start_block,
-							nr_blocks, GFP_NOIO))
+				    nr_blocks, GFP_NOIO, DISCARD_FL_BARRIER))
 				break;
 		}
 
 		lh = se->list.next;
-		if (lh == &si->extent_list)
-			lh = lh->next;
 		se = list_entry(lh, struct swap_extent, list);
 	}
 }
@@ -166,7 +207,8 @@ static int wait_for_discard(void *word)
 #define SWAPFILE_CLUSTER	256
 #define LATENCY_LIMIT		256
 
-static inline unsigned long scan_swap_map(struct swap_info_struct *si)
+static inline unsigned long scan_swap_map(struct swap_info_struct *si,
+					  unsigned char usage)
 {
 	unsigned long offset;
 	unsigned long scan_base;
@@ -272,6 +314,19 @@ checks:
 		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;
 
@@ -284,7 +339,7 @@ checks:
 		si->lowest_bit = si->max;
 		si->highest_bit = 0;
 	}
-	si->swap_map[offset] = 1;
+	si->swap_map[offset] = usage;
 	si->cluster_next = offset + 1;
 	si->flags -= SWP_SCANNING;
 
@@ -350,6 +405,10 @@ scan:
 			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;
@@ -361,6 +420,10 @@ scan:
 			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;
@@ -386,10 +449,10 @@ swp_entry_t get_swap_page(void)
 	nr_swap_pages--;
 
 	for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
-		si = swap_info + type;
+		si = swap_info[type];
 		next = si->next;
 		if (next < 0 ||
-		    (!wrapped && si->prio != swap_info[next].prio)) {
+		    (!wrapped && si->prio != swap_info[next]->prio)) {
 			next = swap_list.head;
 			wrapped++;
 		}
@@ -400,7 +463,8 @@ swp_entry_t get_swap_page(void)
 			continue;
 
 		swap_list.next = next;
-		offset = scan_swap_map(si);
+		/* 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);
@@ -414,16 +478,18 @@ noswap:
 	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->flags & SWP_WRITEOK) {
+	si = swap_info[type];
+	if (si && (si->flags & SWP_WRITEOK)) {
 		nr_swap_pages--;
-		offset = scan_swap_map(si);
+		/* 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);
@@ -434,9 +500,9 @@ swp_entry_t get_swap_page_of_type(int type)
 	return (swp_entry_t) {0};
 }
 
-static struct swap_info_struct * swap_info_get(swp_entry_t entry)
+static struct swap_info_struct *swap_info_get(swp_entry_t entry)
 {
-	struct swap_info_struct * p;
+	struct swap_info_struct *p;
 	unsigned long offset, type;
 
 	if (!entry.val)
@@ -444,7 +510,7 @@ static struct swap_info_struct * swap_info_get(swp_entry_t entry)
 	type = swp_type(entry);
 	if (type >= nr_swapfiles)
 		goto bad_nofile;
-	p = & swap_info[type];
+	p = swap_info[type];
 	if (!(p->flags & SWP_USED))
 		goto bad_device;
 	offset = swp_offset(entry);
@@ -470,25 +536,56 @@ out:
 	return NULL;
 }
 
-static int swap_entry_free(struct swap_info_struct *p, unsigned long offset)
+static unsigned char swap_entry_free(struct swap_info_struct *p,
+				     swp_entry_t entry, unsigned char usage)
 {
-	int count = p->swap_map[offset];
-
-	if (count < SWAP_MAP_MAX) {
-		count--;
-		p->swap_map[offset] = count;
-		if (!count) {
-			if (offset < p->lowest_bit)
-				p->lowest_bit = offset;
-			if (offset > p->highest_bit)
-				p->highest_bit = offset;
-			if (p->prio > swap_info[swap_list.next].prio)
-				swap_list.next = p - swap_info;
-			nr_swap_pages++;
-			p->inuse_pages--;
-		}
+	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) {
+		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--;
 	}
-	return count;
+
+	return usage;
 }
 
 /*
@@ -497,17 +594,36 @@ static int swap_entry_free(struct swap_info_struct *p, unsigned long offset)
  */
 void swap_free(swp_entry_t entry)
 {
-	struct swap_info_struct * p;
+	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) {
-		swap_entry_free(p, swp_offset(entry));
+		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)
 {
@@ -518,8 +634,7 @@ static inline int page_swapcount(struct page *page)
 	entry.val = page_private(page);
 	p = swap_info_get(entry);
 	if (p) {
-		/* Subtract the 1 for the swap cache itself */
-		count = p->swap_map[swp_offset(entry)] - 1;
+		count = swap_count(p->swap_map[swp_offset(entry)]);
 		spin_unlock(&swap_lock);
 	}
 	return count;
@@ -536,6 +651,8 @@ 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);
@@ -544,7 +661,7 @@ int reuse_swap_page(struct page *page)
 			SetPageDirty(page);
 		}
 	}
-	return count == 1;
+	return count <= 1;
 }
 
 /*
@@ -576,12 +693,12 @@ int free_swap_and_cache(swp_entry_t entry)
 	struct swap_info_struct *p;
 	struct page *page = NULL;
 
-	if (is_migration_entry(entry))
+	if (non_swap_entry(entry))
 		return 1;
 
 	p = swap_info_get(entry);
 	if (p) {
-		if (swap_entry_free(p, swp_offset(entry)) == 1) {
+		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);
@@ -618,37 +735,35 @@ int free_swap_and_cache(swp_entry_t entry)
 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 {
 	struct block_device *bdev = NULL;
-	int i;
+	int type;
 
 	if (device)
 		bdev = bdget(device);
 
 	spin_lock(&swap_lock);
-	for (i = 0; i < nr_swapfiles; i++) {
-		struct swap_info_struct *sis = swap_info + i;
+	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 = sis->bdev;
+				*bdev_p = bdgrab(sis->bdev);
 
 			spin_unlock(&swap_lock);
-			return i;
+			return type;
 		}
 		if (bdev == sis->bdev) {
-			struct swap_extent *se;
+			struct swap_extent *se = &sis->first_swap_extent;
 
-			se = list_entry(sis->extent_list.next,
-					struct swap_extent, list);
 			if (se->start_block == offset) {
 				if (bdev_p)
-					*bdev_p = sis->bdev;
+					*bdev_p = bdgrab(sis->bdev);
 
 				spin_unlock(&swap_lock);
 				bdput(bdev);
-				return i;
+				return type;
 			}
 		}
 	}
@@ -660,6 +775,21 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 }
 
 /*
+ * 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)
  *
@@ -669,18 +799,20 @@ unsigned int count_swap_pages(int type, int free)
 {
 	unsigned int n = 0;
 
-	if (type < nr_swapfiles) {
-		spin_lock(&swap_lock);
-		if (swap_info[type].flags & SWP_WRITEOK) {
-			n = swap_info[type].pages;
+	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 -= swap_info[type].inuse_pages;
+				n -= sis->inuse_pages;
 		}
-		spin_unlock(&swap_lock);
 	}
+	spin_unlock(&swap_lock);
 	return n;
 }
-#endif
+#endif /* CONFIG_HIBERNATION */
 
 /*
  * No need to decide whether this PTE shares the swap entry with others,
@@ -695,8 +827,10 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	pte_t *pte;
 	int ret = 1;
 
-	if (mem_cgroup_try_charge(vma->vm_mm, GFP_HIGHUSER_MOVABLE, &ptr))
+	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)))) {
@@ -720,6 +854,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	activate_page(page);
 out:
 	pte_unmap_unlock(pte, ptl);
+out_nolock:
 	return ret;
 }
 
@@ -806,7 +941,7 @@ static int unuse_vma(struct vm_area_struct *vma,
 	unsigned long addr, end, next;
 	int ret;
 
-	if (page->mapping) {
+	if (page_anon_vma(page)) {
 		addr = page_address_in_vma(page, vma);
 		if (addr == -EFAULT)
 			return 0;
@@ -862,7 +997,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
 {
 	unsigned int max = si->max;
 	unsigned int i = prev;
-	int count;
+	unsigned char count;
 
 	/*
 	 * No need for swap_lock here: we're just looking
@@ -885,7 +1020,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
 			i = 1;
 		}
 		count = si->swap_map[i];
-		if (count && count != SWAP_MAP_BAD)
+		if (count && swap_count(count) != SWAP_MAP_BAD)
 			break;
 	}
 	return i;
@@ -898,16 +1033,14 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
  */
 static int try_to_unuse(unsigned int type)
 {
-	struct swap_info_struct * si = &swap_info[type];
+	struct swap_info_struct *si = swap_info[type];
 	struct mm_struct *start_mm;
-	unsigned short *swap_map;
-	unsigned short swcount;
+	unsigned char *swap_map;
+	unsigned char swcount;
 	struct page *page;
 	swp_entry_t entry;
 	unsigned int i = 0;
 	int retval = 0;
-	int reset_overflow = 0;
-	int shmem;
 
 	/*
 	 * When searching mms for an entry, a good strategy is to
@@ -921,8 +1054,7 @@ static int try_to_unuse(unsigned int type)
 	 * 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.  Though it's only a serious concern when an overflowed
-	 * swap count is reset from SWAP_MAP_MAX, preventing a rescan.
+	 * that.
 	 */
 	start_mm = &init_mm;
 	atomic_inc(&init_mm.mm_users);
@@ -984,18 +1116,19 @@ static int try_to_unuse(unsigned int type)
 
 		/*
 		 * Remove all references to entry.
-		 * Whenever we reach init_mm, there's no address space
-		 * to search, but use it as a reminder to search shmem.
 		 */
-		shmem = 0;
 		swcount = *swap_map;
-		if (swcount > 1) {
-			if (start_mm == &init_mm)
-				shmem = shmem_unuse(entry, page);
-			else
-				retval = unuse_mm(start_mm, entry, page);
+		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_map > 1) {
+		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;
@@ -1005,7 +1138,7 @@ static int try_to_unuse(unsigned int type)
 			atomic_inc(&new_start_mm->mm_users);
 			atomic_inc(&prev_mm->mm_users);
 			spin_lock(&mmlist_lock);
-			while (*swap_map > 1 && !retval && !shmem &&
+			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))
@@ -1017,13 +1150,13 @@ static int try_to_unuse(unsigned int type)
 				cond_resched();
 
 				swcount = *swap_map;
-				if (swcount <= 1)
+				if (!swap_count(swcount)) /* any usage ? */
 					;
-				else if (mm == &init_mm) {
+				else if (mm == &init_mm)
 					set_start_mm = 1;
-					shmem = shmem_unuse(entry, page);
-				} else
+				else
 					retval = unuse_mm(mm, entry, page);
+
 				if (set_start_mm && *swap_map < swcount) {
 					mmput(new_start_mm);
 					atomic_inc(&mm->mm_users);
@@ -1037,13 +1170,6 @@ static int try_to_unuse(unsigned int type)
 			mmput(start_mm);
 			start_mm = new_start_mm;
 		}
-		if (shmem) {
-			/* page has already been unlocked and released */
-			if (shmem > 0)
-				continue;
-			retval = shmem;
-			break;
-		}
 		if (retval) {
 			unlock_page(page);
 			page_cache_release(page);
@@ -1051,26 +1177,6 @@ static int try_to_unuse(unsigned int type)
 		}
 
 		/*
-		 * How could swap count reach 0x7fff when the maximum
-		 * pid is 0x7fff, and there's no way to repeat a swap
-		 * page within an mm (except in shmem, where it's the
-		 * shared object which takes the reference count)?
-		 * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
-		 *
-		 * If that's wrong, then we should worry more about
-		 * exit_mmap() and do_munmap() cases described above:
-		 * we might be resetting SWAP_MAP_MAX too early here.
-		 * We know "Undead"s can happen, they're okay, so don't
-		 * report them; but do report if we reset SWAP_MAP_MAX.
-		 */
-		if (*swap_map == SWAP_MAP_MAX) {
-			spin_lock(&swap_lock);
-			*swap_map = 1;
-			spin_unlock(&swap_lock);
-			reset_overflow = 1;
-		}
-
-		/*
 		 * 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,
@@ -1082,8 +1188,15 @@ static int try_to_unuse(unsigned int type)
 		 * 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_map > 1) && PageDirty(page) && PageSwapCache(page)) {
+		if (swap_count(*swap_map) &&
+		     PageDirty(page) && PageSwapCache(page)) {
 			struct writeback_control wbc = {
 				.sync_mode = WB_SYNC_NONE,
 			};
@@ -1121,10 +1234,6 @@ static int try_to_unuse(unsigned int type)
 	}
 
 	mmput(start_mm);
-	if (reset_overflow) {
-		printk(KERN_WARNING "swapoff: cleared swap entry overflow\n");
-		swap_overflow = 0;
-	}
 	return retval;
 }
 
@@ -1137,10 +1246,10 @@ static int try_to_unuse(unsigned int type)
 static void drain_mmlist(void)
 {
 	struct list_head *p, *next;
-	unsigned int i;
+	unsigned int type;
 
-	for (i = 0; i < nr_swapfiles; i++)
-		if (swap_info[i].inuse_pages)
+	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)
@@ -1150,12 +1259,23 @@ static void drain_mmlist(void)
 
 /*
  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
- * corresponds to page offset `offset'.
+ * 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.
  */
-sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
+static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
 {
-	struct swap_extent *se = sis->curr_swap_extent;
-	struct swap_extent *start_se = se;
+	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;
@@ -1165,40 +1285,31 @@ sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
 			return se->start_block + (offset - se->start_page);
 		}
 		lh = se->list.next;
-		if (lh == &sis->extent_list)
-			lh = lh->next;
 		se = list_entry(lh, struct swap_extent, list);
 		sis->curr_swap_extent = se;
 		BUG_ON(se == start_se);		/* It *must* be present */
 	}
 }
 
-#ifdef CONFIG_HIBERNATION
 /*
- * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
- * corresponding to given index in swap_info (swap type).
+ * Returns the page offset into bdev for the specified page's swap entry.
  */
-sector_t swapdev_block(int swap_type, pgoff_t offset)
+sector_t map_swap_page(struct page *page, struct block_device **bdev)
 {
-	struct swap_info_struct *sis;
-
-	if (swap_type >= nr_swapfiles)
-		return 0;
-
-	sis = swap_info + swap_type;
-	return (sis->flags & SWP_WRITEOK) ? map_swap_page(sis, offset) : 0;
+	swp_entry_t entry;
+	entry.val = page_private(page);
+	return map_swap_entry(entry, bdev);
 }
-#endif /* CONFIG_HIBERNATION */
 
 /*
  * Free all of a swapdev's extent information
  */
 static void destroy_swap_extents(struct swap_info_struct *sis)
 {
-	while (!list_empty(&sis->extent_list)) {
+	while (!list_empty(&sis->first_swap_extent.list)) {
 		struct swap_extent *se;
 
-		se = list_entry(sis->extent_list.next,
+		se = list_entry(sis->first_swap_extent.list.next,
 				struct swap_extent, list);
 		list_del(&se->list);
 		kfree(se);
@@ -1219,8 +1330,15 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 	struct swap_extent *new_se;
 	struct list_head *lh;
 
-	lh = sis->extent_list.prev;	/* The highest page extent */
-	if (lh != &sis->extent_list) {
+	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) {
@@ -1240,7 +1358,7 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 	new_se->nr_pages = nr_pages;
 	new_se->start_block = start_block;
 
-	list_add_tail(&new_se->list, &sis->extent_list);
+	list_add_tail(&new_se->list, &sis->first_swap_extent.list);
 	return 1;
 }
 
@@ -1292,7 +1410,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 	if (S_ISBLK(inode->i_mode)) {
 		ret = add_swap_extent(sis, 0, sis->max, 0);
 		*span = sis->pages;
-		goto done;
+		goto out;
 	}
 
 	blkbits = inode->i_blkbits;
@@ -1363,25 +1481,22 @@ reprobe:
 	sis->max = page_no;
 	sis->pages = page_no - 1;
 	sis->highest_bit = page_no - 1;
-done:
-	sis->curr_swap_extent = list_entry(sis->extent_list.prev,
-					struct swap_extent, list);
-	goto out;
+out:
+	return ret;
 bad_bmap:
 	printk(KERN_ERR "swapon: swapfile has holes\n");
 	ret = -EINVAL;
-out:
-	return ret;
+	goto out;
 }
 
-asmlinkage long sys_swapoff(const char __user * specialfile)
+SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
-	struct swap_info_struct * p = NULL;
-	unsigned short *swap_map;
+	struct swap_info_struct *p = NULL;
+	unsigned char *swap_map;
 	struct file *swap_file, *victim;
 	struct address_space *mapping;
 	struct inode *inode;
-	char * pathname;
+	char *pathname;
 	int i, type, prev;
 	int err;
 
@@ -1402,8 +1517,8 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
 	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;
+	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;
@@ -1422,18 +1537,17 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
 		spin_unlock(&swap_lock);
 		goto out_dput;
 	}
-	if (prev < 0) {
+	if (prev < 0)
 		swap_list.head = p->next;
-	} else {
-		swap_info[prev].next = 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--;
+		for (i = p->next; i >= 0; i = swap_info[i]->next)
+			swap_info[i]->prio = p->prio--;
 		least_priority++;
 	}
 	nr_swap_pages -= p->pages;
@@ -1441,9 +1555,9 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
 	p->flags &= ~SWP_WRITEOK;
 	spin_unlock(&swap_lock);
 
-	current->flags |= PF_SWAPOFF;
+	current->flags |= PF_OOM_ORIGIN;
 	err = try_to_unuse(type);
-	current->flags &= ~PF_SWAPOFF;
+	current->flags &= ~PF_OOM_ORIGIN;
 
 	if (err) {
 		/* re-insert swap space back into swap_list */
@@ -1451,16 +1565,16 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
 		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)
+		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 = p - swap_info;
+			swap_list.head = swap_list.next = type;
 		else
-			swap_info[prev].next = p - swap_info;
+			swap_info[prev]->next = type;
 		nr_swap_pages += p->pages;
 		total_swap_pages += p->pages;
 		p->flags |= SWP_WRITEOK;
@@ -1473,6 +1587,9 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
 	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();
@@ -1494,6 +1611,9 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
 	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);
@@ -1517,8 +1637,8 @@ out:
 /* iterator */
 static void *swap_start(struct seq_file *swap, loff_t *pos)
 {
-	struct swap_info_struct *ptr = swap_info;
-	int i;
+	struct swap_info_struct *si;
+	int type;
 	loff_t l = *pos;
 
 	mutex_lock(&swapon_mutex);
@@ -1526,11 +1646,13 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
 	if (!l)
 		return SEQ_START_TOKEN;
 
-	for (i = 0; i < nr_swapfiles; i++, ptr++) {
-		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
+	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 ptr;
+			return si;
 	}
 
 	return NULL;
@@ -1538,21 +1660,21 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
 
 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
 {
-	struct swap_info_struct *ptr;
-	struct swap_info_struct *endptr = swap_info + nr_swapfiles;
+	struct swap_info_struct *si = v;
+	int type;
 
 	if (v == SEQ_START_TOKEN)
-		ptr = swap_info;
-	else {
-		ptr = v;
-		ptr++;
-	}
+		type = 0;
+	else
+		type = si->type + 1;
 
-	for (; ptr < endptr; ptr++) {
-		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
+	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 ptr;
+		return si;
 	}
 
 	return NULL;
@@ -1565,24 +1687,24 @@ static void swap_stop(struct seq_file *swap, void *v)
 
 static int swap_show(struct seq_file *swap, void *v)
 {
-	struct swap_info_struct *ptr = v;
+	struct swap_info_struct *si = v;
 	struct file *file;
 	int len;
 
-	if (ptr == SEQ_START_TOKEN) {
+	if (si == SEQ_START_TOKEN) {
 		seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
 		return 0;
 	}
 
-	file = ptr->swap_file;
+	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",
-			ptr->pages << (PAGE_SHIFT - 10),
-			ptr->inuse_pages << (PAGE_SHIFT - 10),
-			ptr->prio);
+			si->pages << (PAGE_SHIFT - 10),
+			si->inuse_pages << (PAGE_SHIFT - 10),
+			si->prio);
 	return 0;
 }
 
@@ -1627,9 +1749,9 @@ late_initcall(max_swapfiles_check);
  *
  * The swapon system call
  */
-asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
+SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 {
-	struct swap_info_struct * p;
+	struct swap_info_struct *p;
 	char *name = NULL;
 	struct block_device *bdev = NULL;
 	struct file *swap_file = NULL;
@@ -1643,30 +1765,52 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 	sector_t span;
 	unsigned long maxpages = 1;
 	unsigned long swapfilepages;
-	unsigned short *swap_map = NULL;
+	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);
-	p = swap_info;
-	for (type = 0 ; type < nr_swapfiles ; type++,p++)
-		if (!(p->flags & SWP_USED))
+	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)
-		nr_swapfiles = type+1;
-	memset(p, 0, sizeof(*p));
-	INIT_LIST_HEAD(&p->extent_list);
+	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)) {
@@ -1686,7 +1830,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 
 	error = -EBUSY;
 	for (i = 0; i < nr_swapfiles; i++) {
-		struct swap_info_struct *q = &swap_info[i];
+		struct swap_info_struct *q = swap_info[i];
 
 		if (i == type || !q->swap_file)
 			continue;
@@ -1761,6 +1905,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 
 	p->lowest_bit  = 1;
 	p->cluster_next = 1;
+	p->cluster_nr = 0;
 
 	/*
 	 * Find out how many pages are allowed for a single swap
@@ -1796,13 +1941,13 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 		goto bad_swap;
 
 	/* OK, set up the swap map and apply the bad block list */
-	swap_map = vmalloc(maxpages * sizeof(short));
+	swap_map = vmalloc(maxpages);
 	if (!swap_map) {
 		error = -ENOMEM;
 		goto bad_swap;
 	}
 
-	memset(swap_map, 0, maxpages * sizeof(short));
+	memset(swap_map, 0, maxpages);
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
 		int page_nr = swap_header->info.badpages[i];
 		if (page_nr <= 0 || page_nr >= swap_header->info.last_page) {
@@ -1811,6 +1956,11 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 		}
 		swap_map[page_nr] = SWAP_MAP_BAD;
 	}
+
+	error = swap_cgroup_swapon(type, maxpages);
+	if (error)
+		goto bad_swap;
+
 	nr_good_pages = swap_header->info.last_page -
 			swap_header->info.nr_badpages -
 			1 /* header page */;
@@ -1832,12 +1982,14 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 		goto bad_swap;
 	}
 
-	if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
-		p->flags |= SWP_SOLIDSTATE;
-		p->cluster_next = 1 + (random32() % p->highest_bit);
+	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)
+			p->flags |= SWP_DISCARDABLE;
 	}
-	if (discard_swap(p) == 0)
-		p->flags |= SWP_DISCARDABLE;
 
 	mutex_lock(&swapon_mutex);
 	spin_lock(&swap_lock);
@@ -1860,18 +2012,16 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
 
 	/* 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) {
+	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 = p - swap_info;
-	} else {
-		swap_info[prev].next = p - swap_info;
-	}
+	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;
@@ -1882,6 +2032,7 @@ bad_swap:
 		bd_release(bdev);
 	}
 	destroy_swap_extents(p);
+	swap_cgroup_swapoff(type);
 bad_swap_2:
 	spin_lock(&swap_lock);
 	p->swap_file = NULL;
@@ -1907,15 +2058,15 @@ out:
 
 void si_swapinfo(struct sysinfo *val)
 {
-	unsigned int i;
+	unsigned int type;
 	unsigned long nr_to_be_unused = 0;
 
 	spin_lock(&swap_lock);
-	for (i = 0; i < nr_swapfiles; i++) {
-		if (!(swap_info[i].flags & SWP_USED) ||
-		     (swap_info[i].flags & SWP_WRITEOK))
-			continue;
-		nr_to_be_unused += swap_info[i].inuse_pages;
+	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;
@@ -1925,49 +2076,107 @@ void si_swapinfo(struct sysinfo *val)
 /*
  * Verify that a swap entry is valid and increment its swap map count.
  *
- * Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
- * "permanent", but will be reclaimed by the next swapoff.
+ * 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
  */
-int swap_duplicate(swp_entry_t entry)
+static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 {
-	struct swap_info_struct * p;
+	struct swap_info_struct *p;
 	unsigned long offset, type;
-	int result = 0;
+	unsigned char count;
+	unsigned char has_cache;
+	int err = -EINVAL;
 
-	if (is_migration_entry(entry))
-		return 1;
+	if (non_swap_entry(entry))
+		goto out;
 
 	type = swp_type(entry);
 	if (type >= nr_swapfiles)
 		goto bad_file;
-	p = type + swap_info;
+	p = swap_info[type];
 	offset = swp_offset(entry);
 
 	spin_lock(&swap_lock);
-	if (offset < p->max && p->swap_map[offset]) {
-		if (p->swap_map[offset] < SWAP_MAP_MAX - 1) {
-			p->swap_map[offset]++;
-			result = 1;
-		} else if (p->swap_map[offset] <= SWAP_MAP_MAX) {
-			if (swap_overflow++ < 5)
-				printk(KERN_WARNING "swap_dup: swap entry overflow\n");
-			p->swap_map[offset] = SWAP_MAP_MAX;
-			result = 1;
-		}
-	}
+	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 result;
+	return err;
 
 bad_file:
 	printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
 	goto out;
 }
 
-struct swap_info_struct *
-get_swap_info_struct(unsigned type)
+/*
+ * 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.
+ */
+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_info[type];
+	return __swap_duplicate(entry, SWAP_HAS_CACHE);
 }
 
 /*
@@ -1985,7 +2194,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
 	if (!our_page_cluster)	/* no readahead */
 		return 0;
 
-	si = &swap_info[swp_type(entry)];
+	si = swap_info[swp_type(entry)];
 	target = swp_offset(entry);
 	base = (target >> our_page_cluster) << our_page_cluster;
 	end = base + (1 << our_page_cluster);
@@ -2001,7 +2210,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
 		/* Don't read in free or bad pages */
 		if (!si->swap_map[toff])
 			break;
-		if (si->swap_map[toff] == SWAP_MAP_BAD)
+		if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
 			break;
 	}
 	/* Count contiguous allocated slots below our target */
@@ -2009,7 +2218,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
 		/* Don't read in free or bad pages */
 		if (!si->swap_map[toff])
 			break;
-		if (si->swap_map[toff] == SWAP_MAP_BAD)
+		if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
 			break;
 	}
 	spin_unlock(&swap_lock);
@@ -2021,3 +2230,219 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
 	*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);
+			}
+		}
+	}
+}