8 files changed, 147 insertions, 1 deletions

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
new file mode 100644
index 000000000000..eb2a448981ee
--- /dev/null
+++ b/include/linux/ksm.h
@@ -0,0 +1,50 @@
+#ifndef __LINUX_KSM_H
+#define __LINUX_KSM_H
+/*
+ * Memory merging support.
+ *
+ * This code enables dynamic sharing of identical pages found in different
+ * memory areas, even if they are not shared by fork().
+ */
+
+#include <linux/bitops.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+
+#ifdef CONFIG_KSM
+int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
+                unsigned long end, int advice, unsigned long *vm_flags);
+int __ksm_enter(struct mm_struct *mm);
+void __ksm_exit(struct mm_struct *mm);
+
+static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+        if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
+                return __ksm_enter(mm);
+        return 0;
+}
+
+static inline void ksm_exit(struct mm_struct *mm)
+{
+        if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
+                __ksm_exit(mm);
+}
+#else  /* !CONFIG_KSM */
+
+static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
+                unsigned long end, int advice, unsigned long *vm_flags)
+{
+        return 0;
+}
+
+static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+        return 0;
+}
+
+static inline void ksm_exit(struct mm_struct *mm)
+{
+}
+#endif /* !CONFIG_KSM */
+
+#endif
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d3c8ae7c8015..d808cf832c4d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -103,6 +103,7 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_MIXEDMAP     0x10000000      /* Can contain "struct page" and pure PFN pages */
 #define VM_SAO          0x20000000      /* Strong Access Ordering (powerpc) */
 #define VM_PFN_AT_MMAP  0x40000000      /* PFNMAP vma that is fully mapped at mmap time */
+#define VM_MERGEABLE    0x80000000      /* KSM may merge identical pages */
 
 #ifndef VM_STACK_DEFAULT_FLAGS          /* arch can override this */
 #define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8fe351c3914a..8f3e63cb33a6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -434,7 +434,9 @@ extern int get_dumpable(struct mm_struct *mm);
 /* dumpable bits */
 #define MMF_DUMPABLE      0  /* core dump is permitted */
 #define MMF_DUMP_SECURELY 1  /* core file is readable only by root */
+
 #define MMF_DUMPABLE_BITS 2
+#define MMF_DUMPABLE_MASK ((1 << MMF_DUMPABLE_BITS) - 1)
 
 /* coredump filter bits */
 #define MMF_DUMP_ANON_PRIVATE   2
@@ -444,6 +446,7 @@ extern int get_dumpable(struct mm_struct *mm);
 #define MMF_DUMP_ELF_HEADERS    6
 #define MMF_DUMP_HUGETLB_PRIVATE 7
 #define MMF_DUMP_HUGETLB_SHARED  8
+
 #define MMF_DUMP_FILTER_SHIFT   MMF_DUMPABLE_BITS
 #define MMF_DUMP_FILTER_BITS    7
 #define MMF_DUMP_FILTER_MASK \
@@ -457,6 +460,10 @@ extern int get_dumpable(struct mm_struct *mm);
 #else
 # define MMF_DUMP_MASK_DEFAULT_ELF      0
 #endif
+                                        /* leave room for more dump flags */
+#define MMF_VM_MERGEABLE        16      /* KSM may merge identical pages */
+
+#define MMF_INIT_MASK           (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
 struct sighand_struct {
         atomic_t                count;
diff --git a/kernel/fork.c b/kernel/fork.c
index d4638c8cc19e..73a442b7be6d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -49,6 +49,7 @@
 #include <linux/ftrace.h>
 #include <linux/profile.h>
 #include <linux/rmap.h>
+#include <linux/ksm.h>
 #include <linux/acct.h>
 #include <linux/tsacct_kern.h>
 #include <linux/cn_proc.h>
@@ -299,6 +300,9 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
         rb_link = &mm->mm_rb.rb_node;
         rb_parent = NULL;
         pprev = &mm->mmap;
+        retval = ksm_fork(mm, oldmm);
+        if (retval)
+                goto out;
 
         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
                 struct file *file;
@@ -435,7 +439,8 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
         atomic_set(&mm->mm_count, 1);
         init_rwsem(&mm->mmap_sem);
         INIT_LIST_HEAD(&mm->mmlist);
-        mm->flags = (current->mm) ? current->mm->flags : default_dump_filter;
+        mm->flags = (current->mm) ?
+                (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
         mm->core_state = NULL;
         mm->nr_ptes = 0;
         set_mm_counter(mm, file_rss, 0);
@@ -496,6 +501,7 @@ void mmput(struct mm_struct *mm)
 
         if (atomic_dec_and_test(&mm->mm_users)) {
                 exit_aio(mm);
+                ksm_exit(mm);
                 exit_mmap(mm);
                 set_mm_exe_file(mm, NULL);
                 if (!list_empty(&mm->mmlist)) {
diff --git a/mm/Kconfig b/mm/Kconfig
index 3aa519f52e18..c0b6afa178a1 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -214,6 +214,17 @@ config HAVE_MLOCKED_PAGE_BIT
 config MMU_NOTIFIER
         bool
 
+config KSM
+        bool "Enable KSM for page merging"
+        depends on MMU
+        help
+          Enable Kernel Samepage Merging: KSM periodically scans those areas
+          of an application's address space that an app has advised may be
+          mergeable.  When it finds pages of identical content, it replaces
+          the many instances by a single resident page with that content, so
+          saving memory until one or another app needs to modify the content.
+          Recommended for use with KVM, or with other duplicative applications.
+
 config DEFAULT_MMAP_MIN_ADDR
         int "Low address space to protect from user allocation"
         default 4096
diff --git a/mm/Makefile b/mm/Makefile
index ea4b18bd3960..a63bf59a0c77 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_TMPFS_POSIX_ACL) += shmem_acl.o
 obj-$(CONFIG_SLOB) += slob.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
+obj-$(CONFIG_KSM) += ksm.o
 obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
 obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_SLUB) += slub.o
diff --git a/mm/ksm.c b/mm/ksm.c
new file mode 100644
index 000000000000..8b76008fcd32
--- /dev/null
+++ b/mm/ksm.c
@@ -0,0 +1,56 @@
+/*
+ * Initial dummy version just to illustrate KSM's interface to other files.
+ */
+
+#include <linux/errno.h>
+#include <linux/mman.h>
+#include <linux/ksm.h>
+
+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;
+
+        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))
+                        if (__ksm_enter(mm) < 0)
+                                return -EAGAIN;
+
+                *vm_flags |= VM_MERGEABLE;
+                break;
+
+        case MADV_UNMERGEABLE:
+                if (!(*vm_flags & VM_MERGEABLE))
+                        return 0;               /* just ignore the advice */
+
+                /* Unmerge any merged pages here */
+
+                *vm_flags &= ~VM_MERGEABLE;
+                break;
+        }
+
+        return 0;
+}
+
+int __ksm_enter(struct mm_struct *mm)
+{
+        /* Allocate a structure to track mm and link it into KSM's list */
+        set_bit(MMF_VM_MERGEABLE, &mm->flags);
+        return 0;
+}
+
+void __ksm_exit(struct mm_struct *mm)
+{
+        /* Unlink and free all KSM's structures which track this mm */
+        clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+}
diff --git a/mm/madvise.c b/mm/madvise.c
index 66c31264f062..d9ae2067952e 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -11,6 +11,7 @@
 #include <linux/mempolicy.h>
 #include <linux/hugetlb.h>
 #include <linux/sched.h>
+#include <linux/ksm.h>
 
 /*
  * Any behaviour which results in changes to the vma->vm_flags needs to
@@ -63,6 +64,12 @@ static long madvise_behavior(struct vm_area_struct * vma,
                 }
                 new_flags &= ~VM_DONTCOPY;
                 break;
+        case MADV_MERGEABLE:
+        case MADV_UNMERGEABLE:
+                error = ksm_madvise(vma, start, end, behavior, &new_flags);
+                if (error)
+                        goto out;
+                break;
         }
 
         if (new_flags == vma->vm_flags) {
@@ -239,6 +246,10 @@ madvise_behavior_valid(int behavior)
         case MADV_REMOVE:
         case MADV_WILLNEED:
         case MADV_DONTNEED:
+#ifdef CONFIG_KSM
+        case MADV_MERGEABLE:
+        case MADV_UNMERGEABLE:
+#endif
                 return 1;
 
         default:
@@ -273,6 +284,9 @@ madvise_behavior_valid(int behavior)
  *  MADV_DONTFORK - omit this area from child's address space when forking:
  *              typically, to avoid COWing pages pinned by get_user_pages().
  *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
+ *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
+ *              this area with pages of identical content from other such areas.
+ *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
  *
  * return values:
  *  zero    - success