v4.19.13 snapshot.
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
new file mode 100644
index 0000000..161e816
--- /dev/null
+++ b/include/linux/ksm.h
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#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/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/sched.h>
+#include <linux/sched/coredump.h>
+
+struct stable_node;
+struct mem_cgroup;
+
+#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);
+}
+
+/*
+ * When do_swap_page() first faults in from swap what used to be a KSM page,
+ * no problem, it will be assigned to this vma's anon_vma; but thereafter,
+ * it might be faulted into a different anon_vma (or perhaps to a different
+ * offset in the same anon_vma). do_swap_page() cannot do all the locking
+ * needed to reconstitute a cross-anon_vma KSM page: for now it has to make
+ * a copy, and leave remerging the pages to a later pass of ksmd.
+ *
+ * We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE,
+ * but what if the vma was unmerged while the page was swapped out?
+ */
+struct page *ksm_might_need_to_copy(struct page *page,
+ struct vm_area_struct *vma, unsigned long address);
+
+void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc);
+void ksm_migrate_page(struct page *newpage, struct page *oldpage);
+
+#else /* !CONFIG_KSM */
+
+static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+ return 0;
+}
+
+static inline void ksm_exit(struct mm_struct *mm)
+{
+}
+
+#ifdef CONFIG_MMU
+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 struct page *ksm_might_need_to_copy(struct page *page,
+ struct vm_area_struct *vma, unsigned long address)
+{
+ return page;
+}
+
+static inline void rmap_walk_ksm(struct page *page,
+ struct rmap_walk_control *rwc)
+{
+}
+
+static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
+{
+}
+#endif /* CONFIG_MMU */
+#endif /* !CONFIG_KSM */
+
+#endif /* __LINUX_KSM_H */