[PATCH mm-unstable v8 02/31] pgtable: Create struct ptdesc

[Vishal Moola (Oracle)]

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 at gmail.com>
Acked-by: Mike Rapoport (IBM) <rppt at kernel.org>
---
 include/linux/pgtable.h | 71 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 5f36c055794b..1f92514d54b0 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -993,6 +993,77 @@ 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_rcu_head:      For freeing page table pages.
+ * @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.
+ * @__page_mapping:   Aliases with page->mapping. Unused for page tables.
+ * @pt_mm:            Used for x86 pgds.
+ * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only.
+ * @_pt_pad_2:        Padding to ensure proper alignment.
+ * @ptl:              Lock for the page table.
+ * @__page_type:      Same as page->page_type. Unused for page tables.
+ * @_refcount:        Same as page refcount. Used for s390 page tables.
+ * @pt_memcg_data:    Memcg data. Tracked for page tables here.
+ *
+ * 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 rcu_head pt_rcu_head;
+		struct list_head pt_list;
+		struct {
+			unsigned long _pt_pad_1;
+			pgtable_t pmd_huge_pte;
+		};
+	};
+	unsigned long __page_mapping;
+
+	union {
+		struct mm_struct *pt_mm;
+		atomic_t pt_frag_refcount;
+	};
+
+	union {
+		unsigned long _pt_pad_2;
+#if ALLOC_SPLIT_PTLOCKS
+		spinlock_t *ptl;
+#else
+		spinlock_t ptl;
+#endif
+	};
+	unsigned int __page_type;
+	atomic_t _refcount;
+#ifdef CONFIG_MEMCG
+	unsigned long pt_memcg_data;
+#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, __page_mapping);
+TABLE_MATCH(pt_mm, pt_mm);
+TABLE_MATCH(ptl, ptl);
+TABLE_MATCH(rcu_head, pt_rcu_head);
+TABLE_MATCH(page_type, __page_type);
+TABLE_MATCH(_refcount, _refcount);
+#ifdef CONFIG_MEMCG
+TABLE_MATCH(memcg_data, pt_memcg_data);
+#endif
+#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