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-rw-r--r--mm/Kconfig11
-rw-r--r--mm/Makefile1
-rw-r--r--mm/ksm.c56
-rw-r--r--mm/madvise.c14
4 files changed, 82 insertions, 0 deletions
diff --git a/mm/Kconfig b/mm/Kconfig
index 3aa519f..c0b6afa 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 ea4b18b..a63bf59 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 0000000..8b76008
--- /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 66c3126..d9ae206 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
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