Merge branch 'linus' into sched/core

Conflicts:
	fs/proc/array.c

Merge reason: resolve conflict and queue up dependent patch.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1709 insertions, 0 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
new file mode 100644
index 000000000000..bef1af4f77e3
--- /dev/null
+++ b/mm/ksm.c
@@ -0,0 +1,1709 @@
+/*
+ * Memory merging support.
+ *
+ * This code enables dynamic sharing of identical pages found in different
+ * memory areas, even if they are not shared by fork()
+ *
+ * Copyright (C) 2008-2009 Red Hat, Inc.
+ * Authors:
+ *	Izik Eidus
+ *	Andrea Arcangeli
+ *	Chris Wright
+ *	Hugh Dickins
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ */
+
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/mman.h>
+#include <linux/sched.h>
+#include <linux/rwsem.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/spinlock.h>
+#include <linux/jhash.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/wait.h>
+#include <linux/slab.h>
+#include <linux/rbtree.h>
+#include <linux/mmu_notifier.h>
+#include <linux/swap.h>
+#include <linux/ksm.h>
+
+#include <asm/tlbflush.h>
+
+/*
+ * A few notes about the KSM scanning process,
+ * to make it easier to understand the data structures below:
+ *
+ * In order to reduce excessive scanning, KSM sorts the memory pages by their
+ * contents into a data structure that holds pointers to the pages' locations.
+ *
+ * Since the contents of the pages may change at any moment, KSM cannot just
+ * insert the pages into a normal sorted tree and expect it to find anything.
+ * Therefore KSM uses two data structures - the stable and the unstable tree.
+ *
+ * The stable tree holds pointers to all the merged pages (ksm pages), sorted
+ * by their contents.  Because each such page is write-protected, searching on
+ * this tree is fully assured to be working (except when pages are unmapped),
+ * and therefore this tree is called the stable tree.
+ *
+ * In addition to the stable tree, KSM uses a second data structure called the
+ * unstable tree: this tree holds pointers to pages which have been found to
+ * be "unchanged for a period of time".  The unstable tree sorts these pages
+ * by their contents, but since they are not write-protected, KSM cannot rely
+ * upon the unstable tree to work correctly - the unstable tree is liable to
+ * be corrupted as its contents are modified, and so it is called unstable.
+ *
+ * KSM solves this problem by several techniques:
+ *
+ * 1) The unstable tree is flushed every time KSM completes scanning all
+ *    memory areas, and then the tree is rebuilt again from the beginning.
+ * 2) KSM will only insert into the unstable tree, pages whose hash value
+ *    has not changed since the previous scan of all memory areas.
+ * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
+ *    colors of the nodes and not on their contents, assuring that even when
+ *    the tree gets "corrupted" it won't get out of balance, so scanning time
+ *    remains the same (also, searching and inserting nodes in an rbtree uses
+ *    the same algorithm, so we have no overhead when we flush and rebuild).
+ * 4) KSM never flushes the stable tree, which means that even if it were to
+ *    take 10 attempts to find a page in the unstable tree, once it is found,
+ *    it is secured in the stable tree.  (When we scan a new page, we first
+ *    compare it against the stable tree, and then against the unstable tree.)
+ */
+
+/**
+ * struct mm_slot - ksm information per mm that is being scanned
+ * @link: link to the mm_slots hash list
+ * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
+ * @rmap_list: head for this mm_slot's list of rmap_items
+ * @mm: the mm that this information is valid for
+ */
+struct mm_slot {
+	struct hlist_node link;
+	struct list_head mm_list;
+	struct list_head rmap_list;
+	struct mm_struct *mm;
+};
+
+/**
+ * struct ksm_scan - cursor for scanning
+ * @mm_slot: the current mm_slot we are scanning
+ * @address: the next address inside that to be scanned
+ * @rmap_item: the current rmap that we are scanning inside the rmap_list
+ * @seqnr: count of completed full scans (needed when removing unstable node)
+ *
+ * There is only the one ksm_scan instance of this cursor structure.
+ */
+struct ksm_scan {
+	struct mm_slot *mm_slot;
+	unsigned long address;
+	struct rmap_item *rmap_item;
+	unsigned long seqnr;
+};
+
+/**
+ * struct rmap_item - reverse mapping item for virtual addresses
+ * @link: link into mm_slot's rmap_list (rmap_list is per mm)
+ * @mm: the memory structure this rmap_item is pointing into
+ * @address: the virtual address this rmap_item tracks (+ flags in low bits)
+ * @oldchecksum: previous checksum of the page at that virtual address
+ * @node: rb_node of this rmap_item in either unstable or stable tree
+ * @next: next rmap_item hanging off the same node of the stable tree
+ * @prev: previous rmap_item hanging off the same node of the stable tree
+ */
+struct rmap_item {
+	struct list_head link;
+	struct mm_struct *mm;
+	unsigned long address;		/* + low bits used for flags below */
+	union {
+		unsigned int oldchecksum;		/* when unstable */
+		struct rmap_item *next;			/* when stable */
+	};
+	union {
+		struct rb_node node;			/* when tree node */
+		struct rmap_item *prev;			/* in stable list */
+	};
+};
+
+#define SEQNR_MASK	0x0ff	/* low bits of unstable tree seqnr */
+#define NODE_FLAG	0x100	/* is a node of unstable or stable tree */
+#define STABLE_FLAG	0x200	/* is a node or list item of stable tree */
+
+/* The stable and unstable tree heads */
+static struct rb_root root_stable_tree = RB_ROOT;
+static struct rb_root root_unstable_tree = RB_ROOT;
+
+#define MM_SLOTS_HASH_HEADS 1024
+static struct hlist_head *mm_slots_hash;
+
+static struct mm_slot ksm_mm_head = {
+	.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
+};
+static struct ksm_scan ksm_scan = {
+	.mm_slot = &ksm_mm_head,
+};
+
+static struct kmem_cache *rmap_item_cache;
+static struct kmem_cache *mm_slot_cache;
+
+/* The number of nodes in the stable tree */
+static unsigned long ksm_pages_shared;
+
+/* The number of page slots additionally sharing those nodes */
+static unsigned long ksm_pages_sharing;
+
+/* The number of nodes in the unstable tree */
+static unsigned long ksm_pages_unshared;
+
+/* The number of rmap_items in use: to calculate pages_volatile */
+static unsigned long ksm_rmap_items;
+
+/* Limit on the number of unswappable pages used */
+static unsigned long ksm_max_kernel_pages;
+
+/* Number of pages ksmd should scan in one batch */
+static unsigned int ksm_thread_pages_to_scan = 100;
+
+/* Milliseconds ksmd should sleep between batches */
+static unsigned int ksm_thread_sleep_millisecs = 20;
+
+#define KSM_RUN_STOP	0
+#define KSM_RUN_MERGE	1
+#define KSM_RUN_UNMERGE	2
+static unsigned int ksm_run = KSM_RUN_STOP;
+
+static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
+static DEFINE_MUTEX(ksm_thread_mutex);
+static DEFINE_SPINLOCK(ksm_mmlist_lock);
+
+#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
+		sizeof(struct __struct), __alignof__(struct __struct),\
+		(__flags), NULL)
+
+static int __init ksm_slab_init(void)
+{
+	rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
+	if (!rmap_item_cache)
+		goto out;
+
+	mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
+	if (!mm_slot_cache)
+		goto out_free;
+
+	return 0;
+
+out_free:
+	kmem_cache_destroy(rmap_item_cache);
+out:
+	return -ENOMEM;
+}
+
+static void __init ksm_slab_free(void)
+{
+	kmem_cache_destroy(mm_slot_cache);
+	kmem_cache_destroy(rmap_item_cache);
+	mm_slot_cache = NULL;
+}
+
+static inline struct rmap_item *alloc_rmap_item(void)
+{
+	struct rmap_item *rmap_item;
+
+	rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
+	if (rmap_item)
+		ksm_rmap_items++;
+	return rmap_item;
+}
+
+static inline void free_rmap_item(struct rmap_item *rmap_item)
+{
+	ksm_rmap_items--;
+	rmap_item->mm = NULL;	/* debug safety */
+	kmem_cache_free(rmap_item_cache, rmap_item);
+}
+
+static inline struct mm_slot *alloc_mm_slot(void)
+{
+	if (!mm_slot_cache)	/* initialization failed */
+		return NULL;
+	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
+}
+
+static inline void free_mm_slot(struct mm_slot *mm_slot)
+{
+	kmem_cache_free(mm_slot_cache, mm_slot);
+}
+
+static int __init mm_slots_hash_init(void)
+{
+	mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
+				GFP_KERNEL);
+	if (!mm_slots_hash)
+		return -ENOMEM;
+	return 0;
+}
+
+static void __init mm_slots_hash_free(void)
+{
+	kfree(mm_slots_hash);
+}
+
+static struct mm_slot *get_mm_slot(struct mm_struct *mm)
+{
+	struct mm_slot *mm_slot;
+	struct hlist_head *bucket;
+	struct hlist_node *node;
+
+	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
+				% MM_SLOTS_HASH_HEADS];
+	hlist_for_each_entry(mm_slot, node, bucket, link) {
+		if (mm == mm_slot->mm)
+			return mm_slot;
+	}
+	return NULL;
+}
+
+static void insert_to_mm_slots_hash(struct mm_struct *mm,
+				    struct mm_slot *mm_slot)
+{
+	struct hlist_head *bucket;
+
+	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
+				% MM_SLOTS_HASH_HEADS];
+	mm_slot->mm = mm;
+	INIT_LIST_HEAD(&mm_slot->rmap_list);
+	hlist_add_head(&mm_slot->link, bucket);
+}
+
+static inline int in_stable_tree(struct rmap_item *rmap_item)
+{
+	return rmap_item->address & STABLE_FLAG;
+}
+
+/*
+ * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
+ * page tables after it has passed through ksm_exit() - which, if necessary,
+ * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
+ * a special flag: they can just back out as soon as mm_users goes to zero.
+ * ksm_test_exit() is used throughout to make this test for exit: in some
+ * places for correctness, in some places just to avoid unnecessary work.
+ */
+static inline bool ksm_test_exit(struct mm_struct *mm)
+{
+	return atomic_read(&mm->mm_users) == 0;
+}
+
+/*
+ * We use break_ksm to break COW on a ksm page: it's a stripped down
+ *
+ *	if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
+ *		put_page(page);
+ *
+ * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
+ * in case the application has unmapped and remapped mm,addr meanwhile.
+ * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
+ * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
+ */
+static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
+{
+	struct page *page;
+	int ret = 0;
+
+	do {
+		cond_resched();
+		page = follow_page(vma, addr, FOLL_GET);
+		if (!page)
+			break;
+		if (PageKsm(page))
+			ret = handle_mm_fault(vma->vm_mm, vma, addr,
+							FAULT_FLAG_WRITE);
+		else
+			ret = VM_FAULT_WRITE;
+		put_page(page);
+	} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
+	/*
+	 * We must loop because handle_mm_fault() may back out if there's
+	 * any difficulty e.g. if pte accessed bit gets updated concurrently.
+	 *
+	 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
+	 * COW has been broken, even if the vma does not permit VM_WRITE;
+	 * but note that a concurrent fault might break PageKsm for us.
+	 *
+	 * VM_FAULT_SIGBUS could occur if we race with truncation of the
+	 * backing file, which also invalidates anonymous pages: that's
+	 * okay, that truncation will have unmapped the PageKsm for us.
+	 *
+	 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
+	 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
+	 * current task has TIF_MEMDIE set, and will be OOM killed on return
+	 * to user; and ksmd, having no mm, would never be chosen for that.
+	 *
+	 * But if the mm is in a limited mem_cgroup, then the fault may fail
+	 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
+	 * even ksmd can fail in this way - though it's usually breaking ksm
+	 * just to undo a merge it made a moment before, so unlikely to oom.
+	 *
+	 * That's a pity: we might therefore have more kernel pages allocated
+	 * than we're counting as nodes in the stable tree; but ksm_do_scan
+	 * will retry to break_cow on each pass, so should recover the page
+	 * in due course.  The important thing is to not let VM_MERGEABLE
+	 * be cleared while any such pages might remain in the area.
+	 */
+	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
+}
+
+static void break_cow(struct mm_struct *mm, unsigned long addr)
+{
+	struct vm_area_struct *vma;
+
+	down_read(&mm->mmap_sem);
+	if (ksm_test_exit(mm))
+		goto out;
+	vma = find_vma(mm, addr);
+	if (!vma || vma->vm_start > addr)
+		goto out;
+	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
+		goto out;
+	break_ksm(vma, addr);
+out:
+	up_read(&mm->mmap_sem);
+}
+
+static struct page *get_mergeable_page(struct rmap_item *rmap_item)
+{
+	struct mm_struct *mm = rmap_item->mm;
+	unsigned long addr = rmap_item->address;
+	struct vm_area_struct *vma;
+	struct page *page;
+
+	down_read(&mm->mmap_sem);
+	if (ksm_test_exit(mm))
+		goto out;
+	vma = find_vma(mm, addr);
+	if (!vma || vma->vm_start > addr)
+		goto out;
+	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
+		goto out;
+
+	page = follow_page(vma, addr, FOLL_GET);
+	if (!page)
+		goto out;
+	if (PageAnon(page)) {
+		flush_anon_page(vma, page, addr);
+		flush_dcache_page(page);
+	} else {
+		put_page(page);
+out:		page = NULL;
+	}
+	up_read(&mm->mmap_sem);
+	return page;
+}
+
+/*
+ * get_ksm_page: checks if the page at the virtual address in rmap_item
+ * is still PageKsm, in which case we can trust the content of the page,
+ * and it returns the gotten page; but NULL if the page has been zapped.
+ */
+static struct page *get_ksm_page(struct rmap_item *rmap_item)
+{
+	struct page *page;
+
+	page = get_mergeable_page(rmap_item);
+	if (page && !PageKsm(page)) {
+		put_page(page);
+		page = NULL;
+	}
+	return page;
+}
+
+/*
+ * Removing rmap_item from stable or unstable tree.
+ * This function will clean the information from the stable/unstable tree.
+ */
+static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
+{
+	if (in_stable_tree(rmap_item)) {
+		struct rmap_item *next_item = rmap_item->next;
+
+		if (rmap_item->address & NODE_FLAG) {
+			if (next_item) {
+				rb_replace_node(&rmap_item->node,
+						&next_item->node,
+						&root_stable_tree);
+				next_item->address |= NODE_FLAG;
+				ksm_pages_sharing--;
+			} else {
+				rb_erase(&rmap_item->node, &root_stable_tree);
+				ksm_pages_shared--;
+			}
+		} else {
+			struct rmap_item *prev_item = rmap_item->prev;
+
+			BUG_ON(prev_item->next != rmap_item);
+			prev_item->next = next_item;
+			if (next_item) {
+				BUG_ON(next_item->prev != rmap_item);
+				next_item->prev = rmap_item->prev;
+			}
+			ksm_pages_sharing--;
+		}
+
+		rmap_item->next = NULL;
+
+	} else if (rmap_item->address & NODE_FLAG) {
+		unsigned char age;
+		/*
+		 * Usually ksmd can and must skip the rb_erase, because
+		 * root_unstable_tree was already reset to RB_ROOT.
+		 * But be careful when an mm is exiting: do the rb_erase
+		 * if this rmap_item was inserted by this scan, rather
+		 * than left over from before.
+		 */
+		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
+		BUG_ON(age > 1);
+		if (!age)
+			rb_erase(&rmap_item->node, &root_unstable_tree);
+		ksm_pages_unshared--;
+	}
+
+	rmap_item->address &= PAGE_MASK;
+
+	cond_resched();		/* we're called from many long loops */
+}
+
+static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
+				       struct list_head *cur)
+{
+	struct rmap_item *rmap_item;
+
+	while (cur != &mm_slot->rmap_list) {
+		rmap_item = list_entry(cur, struct rmap_item, link);
+		cur = cur->next;
+		remove_rmap_item_from_tree(rmap_item);
+		list_del(&rmap_item->link);
+		free_rmap_item(rmap_item);
+	}
+}
+
+/*
+ * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
+ * than check every pte of a given vma, the locking doesn't quite work for
+ * that - an rmap_item is assigned to the stable tree after inserting ksm
+ * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
+ * rmap_items from parent to child at fork time (so as not to waste time
+ * if exit comes before the next scan reaches it).
+ *
+ * Similarly, although we'd like to remove rmap_items (so updating counts
+ * and freeing memory) when unmerging an area, it's easier to leave that
+ * to the next pass of ksmd - consider, for example, how ksmd might be
+ * in cmp_and_merge_page on one of the rmap_items we would be removing.
+ */
+static int unmerge_ksm_pages(struct vm_area_struct *vma,
+			     unsigned long start, unsigned long end)
+{
+	unsigned long addr;
+	int err = 0;
+
+	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
+		if (ksm_test_exit(vma->vm_mm))
+			break;
+		if (signal_pending(current))
+			err = -ERESTARTSYS;
+		else
+			err = break_ksm(vma, addr);
+	}
+	return err;
+}
+
+#ifdef CONFIG_SYSFS
+/*
+ * Only called through the sysfs control interface:
+ */
+static int unmerge_and_remove_all_rmap_items(void)
+{
+	struct mm_slot *mm_slot;
+	struct mm_struct *mm;
+	struct vm_area_struct *vma;
+	int err = 0;
+
+	spin_lock(&ksm_mmlist_lock);
+	ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
+						struct mm_slot, mm_list);
+	spin_unlock(&ksm_mmlist_lock);
+
+	for (mm_slot = ksm_scan.mm_slot;
+			mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
+		mm = mm_slot->mm;
+		down_read(&mm->mmap_sem);
+		for (vma = mm->mmap; vma; vma = vma->vm_next) {
+			if (ksm_test_exit(mm))
+				break;
+			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
+				continue;
+			err = unmerge_ksm_pages(vma,
+						vma->vm_start, vma->vm_end);
+			if (err)
+				goto error;
+		}
+
+		remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
+
+		spin_lock(&ksm_mmlist_lock);
+		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
+						struct mm_slot, mm_list);
+		if (ksm_test_exit(mm)) {
+			hlist_del(&mm_slot->link);
+			list_del(&mm_slot->mm_list);
+			spin_unlock(&ksm_mmlist_lock);
+
+			free_mm_slot(mm_slot);
+			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+			up_read(&mm->mmap_sem);
+			mmdrop(mm);
+		} else {
+			spin_unlock(&ksm_mmlist_lock);
+			up_read(&mm->mmap_sem);
+		}
+	}
+
+	ksm_scan.seqnr = 0;
+	return 0;
+
+error:
+	up_read(&mm->mmap_sem);
+	spin_lock(&ksm_mmlist_lock);
+	ksm_scan.mm_slot = &ksm_mm_head;
+	spin_unlock(&ksm_mmlist_lock);
+	return err;
+}
+#endif /* CONFIG_SYSFS */
+
+static u32 calc_checksum(struct page *page)
+{
+	u32 checksum;
+	void *addr = kmap_atomic(page, KM_USER0);
+	checksum = jhash2(addr, PAGE_SIZE / 4, 17);
+	kunmap_atomic(addr, KM_USER0);
+	return checksum;
+}
+
+static int memcmp_pages(struct page *page1, struct page *page2)
+{
+	char *addr1, *addr2;
+	int ret;
+
+	addr1 = kmap_atomic(page1, KM_USER0);
+	addr2 = kmap_atomic(page2, KM_USER1);
+	ret = memcmp(addr1, addr2, PAGE_SIZE);
+	kunmap_atomic(addr2, KM_USER1);
+	kunmap_atomic(addr1, KM_USER0);
+	return ret;
+}
+
+static inline int pages_identical(struct page *page1, struct page *page2)
+{
+	return !memcmp_pages(page1, page2);
+}
+
+static int write_protect_page(struct vm_area_struct *vma, struct page *page,
+			      pte_t *orig_pte)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr;
+	pte_t *ptep;
+	spinlock_t *ptl;
+	int swapped;
+	int err = -EFAULT;
+
+	addr = page_address_in_vma(page, vma);
+	if (addr == -EFAULT)
+		goto out;
+
+	ptep = page_check_address(page, mm, addr, &ptl, 0);
+	if (!ptep)
+		goto out;
+
+	if (pte_write(*ptep)) {
+		pte_t entry;
+
+		swapped = PageSwapCache(page);
+		flush_cache_page(vma, addr, page_to_pfn(page));
+		/*
+		 * Ok this is tricky, when get_user_pages_fast() run it doesnt
+		 * take any lock, therefore the check that we are going to make
+		 * with the pagecount against the mapcount is racey and
+		 * O_DIRECT can happen right after the check.
+		 * So we clear the pte and flush the tlb before the check
+		 * this assure us that no O_DIRECT can happen after the check
+		 * or in the middle of the check.
+		 */
+		entry = ptep_clear_flush(vma, addr, ptep);
+		/*
+		 * Check that no O_DIRECT or similar I/O is in progress on the
+		 * page
+		 */
+		if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
+			set_pte_at_notify(mm, addr, ptep, entry);
+			goto out_unlock;
+		}
+		entry = pte_wrprotect(entry);
+		set_pte_at_notify(mm, addr, ptep, entry);
+	}
+	*orig_pte = *ptep;
+	err = 0;
+
+out_unlock:
+	pte_unmap_unlock(ptep, ptl);
+out:
+	return err;
+}
+
+/**
+ * replace_page - replace page in vma by new ksm page
+ * @vma:      vma that holds the pte pointing to oldpage
+ * @oldpage:  the page we are replacing by newpage
+ * @newpage:  the ksm page we replace oldpage by
+ * @orig_pte: the original value of the pte
+ *
+ * Returns 0 on success, -EFAULT on failure.
+ */
+static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
+			struct page *newpage, pte_t orig_pte)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *ptep;
+	spinlock_t *ptl;
+	unsigned long addr;
+	pgprot_t prot;
+	int err = -EFAULT;
+
+	prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
+
+	addr = page_address_in_vma(oldpage, vma);
+	if (addr == -EFAULT)
+		goto out;
+
+	pgd = pgd_offset(mm, addr);
+	if (!pgd_present(*pgd))
+		goto out;
+
+	pud = pud_offset(pgd, addr);
+	if (!pud_present(*pud))
+		goto out;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		goto out;
+
+	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
+	if (!pte_same(*ptep, orig_pte)) {
+		pte_unmap_unlock(ptep, ptl);
+		goto out;
+	}
+
+	get_page(newpage);
+	page_add_ksm_rmap(newpage);
+
+	flush_cache_page(vma, addr, pte_pfn(*ptep));
+	ptep_clear_flush(vma, addr, ptep);
+	set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
+
+	page_remove_rmap(oldpage);
+	put_page(oldpage);
+
+	pte_unmap_unlock(ptep, ptl);
+	err = 0;
+out:
+	return err;
+}
+
+/*
+ * try_to_merge_one_page - take two pages and merge them into one
+ * @vma: the vma that hold the pte pointing into oldpage
+ * @oldpage: the page that we want to replace with newpage
+ * @newpage: the page that we want to map instead of oldpage
+ *
+ * Note:
+ * oldpage should be a PageAnon page, while newpage should be a PageKsm page,
+ * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
+ *
+ * This function returns 0 if the pages were merged, -EFAULT otherwise.
+ */
+static int try_to_merge_one_page(struct vm_area_struct *vma,
+				 struct page *oldpage,
+				 struct page *newpage)
+{
+	pte_t orig_pte = __pte(0);
+	int err = -EFAULT;
+
+	if (!(vma->vm_flags & VM_MERGEABLE))
+		goto out;
+
+	if (!PageAnon(oldpage))
+		goto out;
+
+	get_page(newpage);
+	get_page(oldpage);
+
+	/*
+	 * We need the page lock to read a stable PageSwapCache in
+	 * write_protect_page().  We use trylock_page() instead of
+	 * lock_page() because we don't want to wait here - we
+	 * prefer to continue scanning and merging different pages,
+	 * then come back to this page when it is unlocked.
+	 */
+	if (!trylock_page(oldpage))
+		goto out_putpage;
+	/*
+	 * If this anonymous page is mapped only here, its pte may need
+	 * to be write-protected.  If it's mapped elsewhere, all of its
+	 * ptes are necessarily already write-protected.  But in either
+	 * case, we need to lock and check page_count is not raised.
+	 */
+	if (write_protect_page(vma, oldpage, &orig_pte)) {
+		unlock_page(oldpage);
+		goto out_putpage;
+	}
+	unlock_page(oldpage);
+
+	if (pages_identical(oldpage, newpage))
+		err = replace_page(vma, oldpage, newpage, orig_pte);
+
+out_putpage:
+	put_page(oldpage);
+	put_page(newpage);
+out:
+	return err;
+}
+
+/*
+ * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
+ * but no new kernel page is allocated: kpage must already be a ksm page.
+ */
+static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
+				      unsigned long addr1,
+				      struct page *page1,
+				      struct page *kpage)
+{
+	struct vm_area_struct *vma;
+	int err = -EFAULT;
+
+	down_read(&mm1->mmap_sem);
+	if (ksm_test_exit(mm1))
+		goto out;
+
+	vma = find_vma(mm1, addr1);
+	if (!vma || vma->vm_start > addr1)
+		goto out;
+
+	err = try_to_merge_one_page(vma, page1, kpage);
+out:
+	up_read(&mm1->mmap_sem);
+	return err;
+}
+
+/*
+ * try_to_merge_two_pages - take two identical pages and prepare them
+ * to be merged into one page.
+ *
+ * This function returns 0 if we successfully mapped two identical pages
+ * into one page, -EFAULT otherwise.
+ *
+ * Note that this function allocates a new kernel page: if one of the pages
+ * is already a ksm page, try_to_merge_with_ksm_page should be used.
+ */
+static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
+				  struct page *page1, struct mm_struct *mm2,
+				  unsigned long addr2, struct page *page2)
+{
+	struct vm_area_struct *vma;
+	struct page *kpage;
+	int err = -EFAULT;
+
+	/*
+	 * The number of nodes in the stable tree
+	 * is the number of kernel pages that we hold.
+	 */
+	if (ksm_max_kernel_pages &&
+	    ksm_max_kernel_pages <= ksm_pages_shared)
+		return err;
+
+	kpage = alloc_page(GFP_HIGHUSER);
+	if (!kpage)
+		return err;
+
+	down_read(&mm1->mmap_sem);
+	if (ksm_test_exit(mm1)) {
+		up_read(&mm1->mmap_sem);
+		goto out;
+	}
+	vma = find_vma(mm1, addr1);
+	if (!vma || vma->vm_start > addr1) {
+		up_read(&mm1->mmap_sem);
+		goto out;
+	}
+
+	copy_user_highpage(kpage, page1, addr1, vma);
+	err = try_to_merge_one_page(vma, page1, kpage);
+	up_read(&mm1->mmap_sem);
+
+	if (!err) {
+		err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
+		/*
+		 * If that fails, we have a ksm page with only one pte
+		 * pointing to it: so break it.
+		 */
+		if (err)
+			break_cow(mm1, addr1);
+	}
+out:
+	put_page(kpage);
+	return err;
+}
+
+/*
+ * stable_tree_search - search page inside the stable tree
+ * @page: the page that we are searching identical pages to.
+ * @page2: pointer into identical page that we are holding inside the stable
+ *	   tree that we have found.
+ * @rmap_item: the reverse mapping item
+ *
+ * This function checks if there is a page inside the stable tree
+ * with identical content to the page that we are scanning right now.
+ *
+ * This function return rmap_item pointer to the identical item if found,
+ * NULL otherwise.
+ */
+static struct rmap_item *stable_tree_search(struct page *page,
+					    struct page **page2,
+					    struct rmap_item *rmap_item)
+{
+	struct rb_node *node = root_stable_tree.rb_node;
+
+	while (node) {
+		struct rmap_item *tree_rmap_item, *next_rmap_item;
+		int ret;
+
+		tree_rmap_item = rb_entry(node, struct rmap_item, node);
+		while (tree_rmap_item) {
+			BUG_ON(!in_stable_tree(tree_rmap_item));
+			cond_resched();
+			page2[0] = get_ksm_page(tree_rmap_item);
+			if (page2[0])
+				break;
+			next_rmap_item = tree_rmap_item->next;
+			remove_rmap_item_from_tree(tree_rmap_item);
+			tree_rmap_item = next_rmap_item;
+		}
+		if (!tree_rmap_item)
+			return NULL;
+
+		ret = memcmp_pages(page, page2[0]);
+
+		if (ret < 0) {
+			put_page(page2[0]);
+			node = node->rb_left;
+		} else if (ret > 0) {
+			put_page(page2[0]);
+			node = node->rb_right;
+		} else {
+			return tree_rmap_item;
+		}
+	}
+
+	return NULL;
+}
+
+/*
+ * stable_tree_insert - insert rmap_item pointing to new ksm page
+ * into the stable tree.
+ *
+ * @page: the page that we are searching identical page to inside the stable
+ *	  tree.
+ * @rmap_item: pointer to the reverse mapping item.
+ *
+ * This function returns rmap_item if success, NULL otherwise.
+ */
+static struct rmap_item *stable_tree_insert(struct page *page,
+					    struct rmap_item *rmap_item)
+{
+	struct rb_node **new = &root_stable_tree.rb_node;
+	struct rb_node *parent = NULL;
+
+	while (*new) {
+		struct rmap_item *tree_rmap_item, *next_rmap_item;
+		struct page *tree_page;
+		int ret;
+
+		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
+		while (tree_rmap_item) {
+			BUG_ON(!in_stable_tree(tree_rmap_item));
+			cond_resched();
+			tree_page = get_ksm_page(tree_rmap_item);
+			if (tree_page)
+				break;
+			next_rmap_item = tree_rmap_item->next;
+			remove_rmap_item_from_tree(tree_rmap_item);
+			tree_rmap_item = next_rmap_item;
+		}
+		if (!tree_rmap_item)
+			return NULL;
+
+		ret = memcmp_pages(page, tree_page);
+		put_page(tree_page);
+
+		parent = *new;
+		if (ret < 0)
+			new = &parent->rb_left;
+		else if (ret > 0)
+			new = &parent->rb_right;
+		else {
+			/*
+			 * It is not a bug that stable_tree_search() didn't
+			 * find this node: because at that time our page was
+			 * not yet write-protected, so may have changed since.
+			 */
+			return NULL;
+		}
+	}
+
+	rmap_item->address |= NODE_FLAG | STABLE_FLAG;
+	rmap_item->next = NULL;
+	rb_link_node(&rmap_item->node, parent, new);
+	rb_insert_color(&rmap_item->node, &root_stable_tree);
+
+	ksm_pages_shared++;
+	return rmap_item;
+}
+
+/*
+ * unstable_tree_search_insert - search and insert items into the unstable tree.
+ *
+ * @page: the page that we are going to search for identical page or to insert
+ *	  into the unstable tree
+ * @page2: pointer into identical page that was found inside the unstable tree
+ * @rmap_item: the reverse mapping item of page
+ *
+ * This function searches for a page in the unstable tree identical to the
+ * page currently being scanned; and if no identical page is found in the
+ * tree, we insert rmap_item as a new object into the unstable tree.
+ *
+ * This function returns pointer to rmap_item found to be identical
+ * to the currently scanned page, NULL otherwise.
+ *
+ * This function does both searching and inserting, because they share
+ * the same walking algorithm in an rbtree.
+ */
+static struct rmap_item *unstable_tree_search_insert(struct page *page,
+						struct page **page2,
+						struct rmap_item *rmap_item)
+{
+	struct rb_node **new = &root_unstable_tree.rb_node;
+	struct rb_node *parent = NULL;
+
+	while (*new) {
+		struct rmap_item *tree_rmap_item;
+		int ret;
+
+		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
+		page2[0] = get_mergeable_page(tree_rmap_item);
+		if (!page2[0])
+			return NULL;
+
+		/*
+		 * Don't substitute an unswappable ksm page
+		 * just for one good swappable forked page.
+		 */
+		if (page == page2[0]) {
+			put_page(page2[0]);
+			return NULL;
+		}
+
+		ret = memcmp_pages(page, page2[0]);
+
+		parent = *new;
+		if (ret < 0) {
+			put_page(page2[0]);
+			new = &parent->rb_left;
+		} else if (ret > 0) {
+			put_page(page2[0]);
+			new = &parent->rb_right;
+		} else {
+			return tree_rmap_item;
+		}
+	}
+
+	rmap_item->address |= NODE_FLAG;
+	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
+	rb_link_node(&rmap_item->node, parent, new);
+	rb_insert_color(&rmap_item->node, &root_unstable_tree);
+
+	ksm_pages_unshared++;
+	return NULL;
+}
+
+/*
+ * stable_tree_append - add another rmap_item to the linked list of
+ * rmap_items hanging off a given node of the stable tree, all sharing
+ * the same ksm page.
+ */
+static void stable_tree_append(struct rmap_item *rmap_item,
+			       struct rmap_item *tree_rmap_item)
+{
+	rmap_item->next = tree_rmap_item->next;
+	rmap_item->prev = tree_rmap_item;
+
+	if (tree_rmap_item->next)
+		tree_rmap_item->next->prev = rmap_item;
+
+	tree_rmap_item->next = rmap_item;
+	rmap_item->address |= STABLE_FLAG;
+
+	ksm_pages_sharing++;
+}
+
+/*
+ * cmp_and_merge_page - first see if page can be merged into the stable tree;
+ * if not, compare checksum to previous and if it's the same, see if page can
+ * be inserted into the unstable tree, or merged with a page already there and
+ * both transferred to the stable tree.
+ *
+ * @page: the page that we are searching identical page to.
+ * @rmap_item: the reverse mapping into the virtual address of this page
+ */
+static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
+{
+	struct page *page2[1];
+	struct rmap_item *tree_rmap_item;
+	unsigned int checksum;
+	int err;
+
+	if (in_stable_tree(rmap_item))
+		remove_rmap_item_from_tree(rmap_item);
+
+	/* We first start with searching the page inside the stable tree */
+	tree_rmap_item = stable_tree_search(page, page2, rmap_item);
+	if (tree_rmap_item) {
+		if (page == page2[0])			/* forked */
+			err = 0;
+		else
+			err = try_to_merge_with_ksm_page(rmap_item->mm,
+							 rmap_item->address,
+							 page, page2[0]);
+		put_page(page2[0]);
+
+		if (!err) {
+			/*
+			 * The page was successfully merged:
+			 * add its rmap_item to the stable tree.
+			 */
+			stable_tree_append(rmap_item, tree_rmap_item);
+		}
+		return;
+	}
+
+	/*
+	 * A ksm page might have got here by fork, but its other
+	 * references have already been removed from the stable tree.
+	 * Or it might be left over from a break_ksm which failed
+	 * when the mem_cgroup had reached its limit: try again now.
+	 */
+	if (PageKsm(page))
+		break_cow(rmap_item->mm, rmap_item->address);
+
+	/*
+	 * In case the hash value of the page was changed from the last time we
+	 * have calculated it, this page to be changed frequely, therefore we
+	 * don't want to insert it to the unstable tree, and we don't want to
+	 * waste our time to search if there is something identical to it there.
+	 */
+	checksum = calc_checksum(page);
+	if (rmap_item->oldchecksum != checksum) {
+		rmap_item->oldchecksum = checksum;
+		return;
+	}
+
+	tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
+	if (tree_rmap_item) {
+		err = try_to_merge_two_pages(rmap_item->mm,
+					     rmap_item->address, page,
+					     tree_rmap_item->mm,
+					     tree_rmap_item->address, page2[0]);
+		/*
+		 * As soon as we merge this page, we want to remove the
+		 * rmap_item of the page we have merged with from the unstable
+		 * tree, and insert it instead as new node in the stable tree.
+		 */
+		if (!err) {
+			rb_erase(&tree_rmap_item->node, &root_unstable_tree);
+			tree_rmap_item->address &= ~NODE_FLAG;
+			ksm_pages_unshared--;
+
+			/*
+			 * If we fail to insert the page into the stable tree,
+			 * we will have 2 virtual addresses that are pointing
+			 * to a ksm page left outside the stable tree,
+			 * in which case we need to break_cow on both.
+			 */
+			if (stable_tree_insert(page2[0], tree_rmap_item))
+				stable_tree_append(rmap_item, tree_rmap_item);
+			else {
+				break_cow(tree_rmap_item->mm,
+						tree_rmap_item->address);
+				break_cow(rmap_item->mm, rmap_item->address);
+			}
+		}
+
+		put_page(page2[0]);
+	}
+}
+
+static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
+					    struct list_head *cur,
+					    unsigned long addr)
+{
+	struct rmap_item *rmap_item;
+
+	while (cur != &mm_slot->rmap_list) {
+		rmap_item = list_entry(cur, struct rmap_item, link);
+		if ((rmap_item->address & PAGE_MASK) == addr) {
+			if (!in_stable_tree(rmap_item))
+				remove_rmap_item_from_tree(rmap_item);
+			return rmap_item;
+		}
+		if (rmap_item->address > addr)
+			break;
+		cur = cur->next;
+		remove_rmap_item_from_tree(rmap_item);
+		list_del(&rmap_item->link);
+		free_rmap_item(rmap_item);
+	}
+
+	rmap_item = alloc_rmap_item();
+	if (rmap_item) {
+		/* It has already been zeroed */
+		rmap_item->mm = mm_slot->mm;
+		rmap_item->address = addr;
+		list_add_tail(&rmap_item->link, cur);
+	}
+	return rmap_item;
+}
+
+static struct rmap_item *scan_get_next_rmap_item(struct page **page)
+{
+	struct mm_struct *mm;
+	struct mm_slot *slot;
+	struct vm_area_struct *vma;
+	struct rmap_item *rmap_item;
+
+	if (list_empty(&ksm_mm_head.mm_list))
+		return NULL;
+
+	slot = ksm_scan.mm_slot;
+	if (slot == &ksm_mm_head) {
+		root_unstable_tree = RB_ROOT;
+
+		spin_lock(&ksm_mmlist_lock);
+		slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
+		ksm_scan.mm_slot = slot;
+		spin_unlock(&ksm_mmlist_lock);
+next_mm:
+		ksm_scan.address = 0;
+		ksm_scan.rmap_item = list_entry(&slot->rmap_list,
+						struct rmap_item, link);
+	}
+
+	mm = slot->mm;
+	down_read(&mm->mmap_sem);
+	if (ksm_test_exit(mm))
+		vma = NULL;
+	else
+		vma = find_vma(mm, ksm_scan.address);
+
+	for (; vma; vma = vma->vm_next) {
+		if (!(vma->vm_flags & VM_MERGEABLE))
+			continue;
+		if (ksm_scan.address < vma->vm_start)
+			ksm_scan.address = vma->vm_start;
+		if (!vma->anon_vma)
+			ksm_scan.address = vma->vm_end;
+
+		while (ksm_scan.address < vma->vm_end) {
+			if (ksm_test_exit(mm))
+				break;
+			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
+			if (*page && PageAnon(*page)) {
+				flush_anon_page(vma, *page, ksm_scan.address);
+				flush_dcache_page(*page);
+				rmap_item = get_next_rmap_item(slot,
+					ksm_scan.rmap_item->link.next,
+					ksm_scan.address);
+				if (rmap_item) {
+					ksm_scan.rmap_item = rmap_item;
+					ksm_scan.address += PAGE_SIZE;
+				} else
+					put_page(*page);
+				up_read(&mm->mmap_sem);
+				return rmap_item;
+			}
+			if (*page)
+				put_page(*page);
+			ksm_scan.address += PAGE_SIZE;
+			cond_resched();
+		}
+	}
+
+	if (ksm_test_exit(mm)) {
+		ksm_scan.address = 0;
+		ksm_scan.rmap_item = list_entry(&slot->rmap_list,
+						struct rmap_item, link);
+	}
+	/*
+	 * Nuke all the rmap_items that are above this current rmap:
+	 * because there were no VM_MERGEABLE vmas with such addresses.
+	 */
+	remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
+
+	spin_lock(&ksm_mmlist_lock);
+	ksm_scan.mm_slot = list_entry(slot->mm_list.next,
+						struct mm_slot, mm_list);
+	if (ksm_scan.address == 0) {
+		/*
+		 * We've completed a full scan of all vmas, holding mmap_sem
+		 * throughout, and found no VM_MERGEABLE: so do the same as
+		 * __ksm_exit does to remove this mm from all our lists now.
+		 * This applies either when cleaning up after __ksm_exit
+		 * (but beware: we can reach here even before __ksm_exit),
+		 * or when all VM_MERGEABLE areas have been unmapped (and
+		 * mmap_sem then protects against race with MADV_MERGEABLE).
+		 */
+		hlist_del(&slot->link);
+		list_del(&slot->mm_list);
+		spin_unlock(&ksm_mmlist_lock);
+
+		free_mm_slot(slot);
+		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+		up_read(&mm->mmap_sem);
+		mmdrop(mm);
+	} else {
+		spin_unlock(&ksm_mmlist_lock);
+		up_read(&mm->mmap_sem);
+	}
+
+	/* Repeat until we've completed scanning the whole list */
+	slot = ksm_scan.mm_slot;
+	if (slot != &ksm_mm_head)
+		goto next_mm;
+
+	ksm_scan.seqnr++;
+	return NULL;
+}
+
+/**
+ * ksm_do_scan  - the ksm scanner main worker function.
+ * @scan_npages - number of pages we want to scan before we return.
+ */
+static void ksm_do_scan(unsigned int scan_npages)
+{
+	struct rmap_item *rmap_item;
+	struct page *page;
+
+	while (scan_npages--) {
+		cond_resched();
+		rmap_item = scan_get_next_rmap_item(&page);
+		if (!rmap_item)
+			return;
+		if (!PageKsm(page) || !in_stable_tree(rmap_item))
+			cmp_and_merge_page(page, rmap_item);
+		else if (page_mapcount(page) == 1) {
+			/*
+			 * Replace now-unshared ksm page by ordinary page.
+			 */
+			break_cow(rmap_item->mm, rmap_item->address);
+			remove_rmap_item_from_tree(rmap_item);
+			rmap_item->oldchecksum = calc_checksum(page);
+		}
+		put_page(page);
+	}
+}
+
+static int ksmd_should_run(void)
+{
+	return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
+}
+
+static int ksm_scan_thread(void *nothing)
+{
+	set_user_nice(current, 5);
+
+	while (!kthread_should_stop()) {
+		mutex_lock(&ksm_thread_mutex);
+		if (ksmd_should_run())
+			ksm_do_scan(ksm_thread_pages_to_scan);
+		mutex_unlock(&ksm_thread_mutex);
+
+		if (ksmd_should_run()) {
+			schedule_timeout_interruptible(
+				msecs_to_jiffies(ksm_thread_sleep_millisecs));
+		} else {
+			wait_event_interruptible(ksm_thread_wait,
+				ksmd_should_run() || kthread_should_stop());
+		}
+	}
+	return 0;
+}
+
+int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
+		unsigned long end, int advice, unsigned long *vm_flags)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	int err;
+
+	switch (advice) {
+	case MADV_MERGEABLE:
+		/*
+		 * Be somewhat over-protective for now!
+		 */
+		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
+				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
+				 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
+				 VM_MIXEDMAP  | VM_SAO))
+			return 0;		/* just ignore the advice */
+
+		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+			err = __ksm_enter(mm);
+			if (err)
+				return err;
+		}
+
+		*vm_flags |= VM_MERGEABLE;
+		break;
+
+	case MADV_UNMERGEABLE:
+		if (!(*vm_flags & VM_MERGEABLE))
+			return 0;		/* just ignore the advice */
+
+		if (vma->anon_vma) {
+			err = unmerge_ksm_pages(vma, start, end);
+			if (err)
+				return err;
+		}
+
+		*vm_flags &= ~VM_MERGEABLE;
+		break;
+	}
+
+	return 0;
+}
+
+int __ksm_enter(struct mm_struct *mm)
+{
+	struct mm_slot *mm_slot;
+	int needs_wakeup;
+
+	mm_slot = alloc_mm_slot();
+	if (!mm_slot)
+		return -ENOMEM;
+
+	/* Check ksm_run too?  Would need tighter locking */
+	needs_wakeup = list_empty(&ksm_mm_head.mm_list);
+
+	spin_lock(&ksm_mmlist_lock);
+	insert_to_mm_slots_hash(mm, mm_slot);
+	/*
+	 * Insert just behind the scanning cursor, to let the area settle
+	 * down a little; when fork is followed by immediate exec, we don't
+	 * want ksmd to waste time setting up and tearing down an rmap_list.
+	 */
+	list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
+	spin_unlock(&ksm_mmlist_lock);
+
+	set_bit(MMF_VM_MERGEABLE, &mm->flags);
+	atomic_inc(&mm->mm_count);
+
+	if (needs_wakeup)
+		wake_up_interruptible(&ksm_thread_wait);
+
+	return 0;
+}
+
+void __ksm_exit(struct mm_struct *mm)
+{
+	struct mm_slot *mm_slot;
+	int easy_to_free = 0;
+
+	/*
+	 * This process is exiting: if it's straightforward (as is the
+	 * case when ksmd was never running), free mm_slot immediately.
+	 * But if it's at the cursor or has rmap_items linked to it, use
+	 * mmap_sem to synchronize with any break_cows before pagetables
+	 * are freed, and leave the mm_slot on the list for ksmd to free.
+	 * Beware: ksm may already have noticed it exiting and freed the slot.
+	 */
+
+	spin_lock(&ksm_mmlist_lock);
+	mm_slot = get_mm_slot(mm);
+	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
+		if (list_empty(&mm_slot->rmap_list)) {
+			hlist_del(&mm_slot->link);
+			list_del(&mm_slot->mm_list);
+			easy_to_free = 1;
+		} else {
+			list_move(&mm_slot->mm_list,
+				  &ksm_scan.mm_slot->mm_list);
+		}
+	}
+	spin_unlock(&ksm_mmlist_lock);
+
+	if (easy_to_free) {
+		free_mm_slot(mm_slot);
+		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+		mmdrop(mm);
+	} else if (mm_slot) {
+		down_write(&mm->mmap_sem);
+		up_write(&mm->mmap_sem);
+	}
+}
+
+#ifdef CONFIG_SYSFS
+/*
+ * This all compiles without CONFIG_SYSFS, but is a waste of space.
+ */
+
+#define KSM_ATTR_RO(_name) \
+	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+#define KSM_ATTR(_name) \
+	static struct kobj_attribute _name##_attr = \
+		__ATTR(_name, 0644, _name##_show, _name##_store)
+
+static ssize_t sleep_millisecs_show(struct kobject *kobj,
+				    struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
+}
+
+static ssize_t sleep_millisecs_store(struct kobject *kobj,
+				     struct kobj_attribute *attr,
+				     const char *buf, size_t count)
+{
+	unsigned long msecs;
+	int err;
+
+	err = strict_strtoul(buf, 10, &msecs);
+	if (err || msecs > UINT_MAX)
+		return -EINVAL;
+
+	ksm_thread_sleep_millisecs = msecs;
+
+	return count;
+}
+KSM_ATTR(sleep_millisecs);
+
+static ssize_t pages_to_scan_show(struct kobject *kobj,
+				  struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
+}
+
+static ssize_t pages_to_scan_store(struct kobject *kobj,
+				   struct kobj_attribute *attr,
+				   const char *buf, size_t count)
+{
+	int err;
+	unsigned long nr_pages;
+
+	err = strict_strtoul(buf, 10, &nr_pages);
+	if (err || nr_pages > UINT_MAX)
+		return -EINVAL;
+
+	ksm_thread_pages_to_scan = nr_pages;
+
+	return count;
+}
+KSM_ATTR(pages_to_scan);
+
+static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
+			char *buf)
+{
+	return sprintf(buf, "%u\n", ksm_run);
+}
+
+static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
+			 const char *buf, size_t count)
+{
+	int err;
+	unsigned long flags;
+
+	err = strict_strtoul(buf, 10, &flags);
+	if (err || flags > UINT_MAX)
+		return -EINVAL;
+	if (flags > KSM_RUN_UNMERGE)
+		return -EINVAL;
+
+	/*
+	 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
+	 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
+	 * breaking COW to free the unswappable pages_shared (but leaves
+	 * mm_slots on the list for when ksmd may be set running again).
+	 */
+
+	mutex_lock(&ksm_thread_mutex);
+	if (ksm_run != flags) {
+		ksm_run = flags;
+		if (flags & KSM_RUN_UNMERGE) {
+			current->flags |= PF_OOM_ORIGIN;
+			err = unmerge_and_remove_all_rmap_items();
+			current->flags &= ~PF_OOM_ORIGIN;
+			if (err) {
+				ksm_run = KSM_RUN_STOP;
+				count = err;
+			}
+		}
+	}
+	mutex_unlock(&ksm_thread_mutex);
+
+	if (flags & KSM_RUN_MERGE)
+		wake_up_interruptible(&ksm_thread_wait);
+
+	return count;
+}
+KSM_ATTR(run);
+
+static ssize_t max_kernel_pages_store(struct kobject *kobj,
+				      struct kobj_attribute *attr,
+				      const char *buf, size_t count)
+{
+	int err;
+	unsigned long nr_pages;
+
+	err = strict_strtoul(buf, 10, &nr_pages);
+	if (err)
+		return -EINVAL;
+
+	ksm_max_kernel_pages = nr_pages;
+
+	return count;
+}
+
+static ssize_t max_kernel_pages_show(struct kobject *kobj,
+				     struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
+}
+KSM_ATTR(max_kernel_pages);
+
+static ssize_t pages_shared_show(struct kobject *kobj,
+				 struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", ksm_pages_shared);
+}
+KSM_ATTR_RO(pages_shared);
+
+static ssize_t pages_sharing_show(struct kobject *kobj,
+				  struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", ksm_pages_sharing);
+}
+KSM_ATTR_RO(pages_sharing);
+
+static ssize_t pages_unshared_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", ksm_pages_unshared);
+}
+KSM_ATTR_RO(pages_unshared);
+
+static ssize_t pages_volatile_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	long ksm_pages_volatile;
+
+	ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
+				- ksm_pages_sharing - ksm_pages_unshared;
+	/*
+	 * It was not worth any locking to calculate that statistic,
+	 * but it might therefore sometimes be negative: conceal that.
+	 */
+	if (ksm_pages_volatile < 0)
+		ksm_pages_volatile = 0;
+	return sprintf(buf, "%ld\n", ksm_pages_volatile);
+}
+KSM_ATTR_RO(pages_volatile);
+
+static ssize_t full_scans_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%lu\n", ksm_scan.seqnr);
+}
+KSM_ATTR_RO(full_scans);
+
+static struct attribute *ksm_attrs[] = {
+	&sleep_millisecs_attr.attr,
+	&pages_to_scan_attr.attr,
+	&run_attr.attr,
+	&max_kernel_pages_attr.attr,
+	&pages_shared_attr.attr,
+	&pages_sharing_attr.attr,
+	&pages_unshared_attr.attr,
+	&pages_volatile_attr.attr,
+	&full_scans_attr.attr,
+	NULL,
+};
+
+static struct attribute_group ksm_attr_group = {
+	.attrs = ksm_attrs,
+	.name = "ksm",
+};
+#endif /* CONFIG_SYSFS */
+
+static int __init ksm_init(void)
+{
+	struct task_struct *ksm_thread;
+	int err;
+
+	ksm_max_kernel_pages = totalram_pages / 4;
+
+	err = ksm_slab_init();
+	if (err)
+		goto out;
+
+	err = mm_slots_hash_init();
+	if (err)
+		goto out_free1;
+
+	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
+	if (IS_ERR(ksm_thread)) {
+		printk(KERN_ERR "ksm: creating kthread failed\n");
+		err = PTR_ERR(ksm_thread);
+		goto out_free2;
+	}
+
+#ifdef CONFIG_SYSFS
+	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
+	if (err) {
+		printk(KERN_ERR "ksm: register sysfs failed\n");
+		kthread_stop(ksm_thread);
+		goto out_free2;
+	}
+#else
+	ksm_run = KSM_RUN_MERGE;	/* no way for user to start it */
+
+#endif /* CONFIG_SYSFS */
+
+	return 0;
+
+out_free2:
+	mm_slots_hash_free();
+out_free1:
+	ksm_slab_free();
+out:
+	return err;
+}
+module_init(ksm_init)