From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
I found the struct { union { struct { union { struct { } } } } }
layout rather confusing. Fortunately, there is an easier way to write
this. The innermost union is of four things which are the size of an
int, so the ones which are used by slab/slob/slub can be pulled up
two levels to be in the outermost union with 'counters'. That leaves
us with struct { union { struct { atomic_t; atomic_t; } } } which
has the same layout, but is easier to read.
Output from the current git version of pahole, diffed with -uw to ignore
the whitespace changes from the indentation:
@@ -11,9 +11,6 @@
}; /* 16 8 */
union {
long unsigned int counters; /* 24 8 */
- struct {
- union {
- atomic_t _mapcount; /* 24 4 */
unsigned int active; /* 24 4 */
struct {
unsigned int inuse:16; /* 24:16 4 */
@@ -21,7 +18,8 @@
unsigned int frozen:1; /* 24: 0 4 */
}; /* 24 4 */
int units; /* 24 4 */
- }; /* 24 4 */
+ struct {
+ atomic_t _mapcount; /* 24 4 */
atomic_t _refcount; /* 28 4 */
}; /* 24 8 */
}; /* 24 8 */
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
---
include/linux/mm_types.h | 40 +++++++++++++++++++---------------------
1 file changed, 19 insertions(+), 21 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4509f0cfaf39..27973166af28 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -84,28 +84,26 @@ struct page {
*/
unsigned counters;
#endif
- struct {
+ unsigned int active; /* SLAB */
+ struct { /* SLUB */
+ unsigned inuse:16;
+ unsigned objects:15;
+ unsigned frozen:1;
+ };
+ int units; /* SLOB */
+
+ struct { /* Page cache */
+ /*
+ * Count of ptes mapped in mms, to show when
+ * page is mapped & limit reverse map searches.
+ *
+ * Extra information about page type may be
+ * stored here for pages that are never mapped,
+ * in which case the value MUST BE <= -2.
+ * See page-flags.h for more details.
+ */
+ atomic_t _mapcount;
- union {
- /*
- * Count of ptes mapped in mms, to show when
- * page is mapped & limit reverse map searches.
- *
- * Extra information about page type may be
- * stored here for pages that are never mapped,
- * in which case the value MUST BE <= -2.
- * See page-flags.h for more details.
- */
- atomic_t _mapcount;
-
- unsigned int active; /* SLAB */
- struct { /* SLUB */
- unsigned inuse:16;
- unsigned objects:15;
- unsigned frozen:1;
- };
- int units; /* SLOB */
- };
/*
* Usage count, *USE WRAPPER FUNCTION* when manual
* accounting. See page_ref.h
--
2.15.1
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