From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Keeping the refcount in the union only encourages people to put
something else in the union which will overlap with _refcount and
eventually explode messily. pahole reports no fields change location.
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
include/linux/mm_types.h | 25 ++++++++++---------------
1 file changed, 10 insertions(+), 15 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 23378a789af4..9828cd170251 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -113,7 +113,13 @@ struct page {
};
};
- union {
+ union { /* This union is 4 bytes in size. */
+ /*
+ * If the page can be mapped to userspace, encodes the number
+ * of times this page is referenced by a page table.
+ */
+ atomic_t _mapcount;
+
/*
* If the page is neither PageSlab nor mappable to userspace,
* the value stored here may help determine what this page
@@ -124,22 +130,11 @@ struct page {
unsigned int active; /* SLAB */
int units; /* SLOB */
-
- struct { /* Page cache */
- /*
- * Count of ptes mapped in mms, to show when
- * page is mapped & limit reverse map searches.
- */
- atomic_t _mapcount;
-
- /*
- * Usage count, *USE WRAPPER FUNCTION* when manual
- * accounting. See page_ref.h
- */
- atomic_t _refcount;
- };
};
+ /* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
+ atomic_t _refcount;
+
/*
* WARNING: bit 0 of the first word encode PageTail(). That means
* the rest users of the storage space MUST NOT use the bit to
--
2.17.0
