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Subject[PATCH] mm: add fields for compound destructor and order into struct page
Date
Currently, we use lru.next/lru.prev plus cast to access or set
destructor and order of compound page.

Let's replace it with explicit fields in struct page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/mm.h | 9 ++++-----
include/linux/mm_types.h | 8 ++++++++
2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5bfd9b9756fa..a8de6fe11d0a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -525,29 +525,28 @@ int split_free_page(struct page *page);
* prototype for that function and accessor functions.
* These are _only_ valid on the head of a PG_compound page.
*/
-typedef void compound_page_dtor(struct page *);

static inline void set_compound_page_dtor(struct page *page,
compound_page_dtor *dtor)
{
- page[1].lru.next = (void *)dtor;
+ page[1].compound_dtor = dtor;
}

static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
{
- return (compound_page_dtor *)page[1].lru.next;
+ return page[1].compound_dtor;
}

static inline int compound_order(struct page *page)
{
if (!PageHead(page))
return 0;
- return (unsigned long)page[1].lru.prev;
+ return page[1].compound_order;
}

static inline void set_compound_order(struct page *page, unsigned long order)
{
- page[1].lru.prev = (void *)order;
+ page[1].compound_order = order;
}

#ifdef CONFIG_MMU
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 03945eef1350..cbc71f32a53c 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -28,6 +28,8 @@ struct mem_cgroup;
IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))
#define ALLOC_SPLIT_PTLOCKS (SPINLOCK_SIZE > BITS_PER_LONG/8)

+typedef void compound_page_dtor(struct page *);
+
/*
* Each physical page in the system has a struct page associated with
* it to keep track of whatever it is we are using the page for at the
@@ -131,6 +133,12 @@ struct page {
struct rcu_head rcu_head; /* Used by SLAB
* when destroying via RCU
*/
+ /* First tail page of compound page */
+ struct {
+ compound_page_dtor *compound_dtor;
+ unsigned long compound_order;
+ };
+
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
pgtable_t pmd_huge_pte; /* protected by page->ptl */
#endif
--
2.1.3


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