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>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
---
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
