[PATCH v4 04/34] pgtable: Create struct ptdesc

["Vishal Moola (Oracle)" <vishal.moola@xxxxxxxxx>]

Currently, page table information is stored within struct page. As part
of simplifying struct page, create struct ptdesc for page table
information.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
---
 include/linux/pgtable.h | 51 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index c5a51481bbb9..330de96ebfd6 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -975,6 +975,57 @@ static inline void ptep_modify_prot_commit(struct 
vm_area_struct *vma,
 #endif /* __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION */
 #endif /* CONFIG_MMU */
 
+
+/**
+ * struct ptdesc - Memory descriptor for page tables.
+ * @__page_flags: Same as page flags. Unused for page tables.
+ * @pt_list: List of used page tables. Used for s390 and x86.
+ * @_pt_pad_1: Padding that aliases with page's compound head.
+ * @pmd_huge_pte: Protected by ptdesc->ptl, used for THPs.
+ * @_pt_s390_gaddr: Aliases with page's mapping. Used for s390 gmap only.
+ * @pt_mm: Used for x86 pgds.
+ * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 
only.
+ * @ptl: Lock for the page table.
+ *
+ * This struct overlays struct page for now. Do not modify without a good
+ * understanding of the issues.
+ */
+struct ptdesc {
+       unsigned long __page_flags;
+
+       union {
+               struct list_head pt_list;
+               struct {
+                       unsigned long _pt_pad_1;
+                       pgtable_t pmd_huge_pte;
+               };
+       };
+       unsigned long _pt_s390_gaddr;
+
+       union {
+               struct mm_struct *pt_mm;
+               atomic_t pt_frag_refcount;
+       };
+
+#if ALLOC_SPLIT_PTLOCKS
+       spinlock_t *ptl;
+#else
+       spinlock_t ptl;
+#endif
+};
+
+#define TABLE_MATCH(pg, pt)                                            \
+       static_assert(offsetof(struct page, pg) == offsetof(struct ptdesc, pt))
+TABLE_MATCH(flags, __page_flags);
+TABLE_MATCH(compound_head, pt_list);
+TABLE_MATCH(compound_head, _pt_pad_1);
+TABLE_MATCH(pmd_huge_pte, pmd_huge_pte);
+TABLE_MATCH(mapping, _pt_s390_gaddr);
+TABLE_MATCH(pt_mm, pt_mm);
+TABLE_MATCH(ptl, ptl);
+#undef TABLE_MATCH
+static_assert(sizeof(struct ptdesc) <= sizeof(struct page));
+
 /*
  * No-op macros that just return the current protection value. Defined here
  * because these macros can be used even if CONFIG_MMU is not defined.
-- 
2.40.1