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Subject[mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures
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This change makes it so that we use the same approach that was already in
use on Sparc on all the archtectures that support a 64b long.

This is mostly motivated by the fact that 8 to 10 store/move instructions
are likely always going to be faster than having to call into a function
that is not specialized for handling page init.

An added advantage to doing it this way is that the compiler can get away
with combining writes in the __init_single_page call. As a result the
memset call will be reduced to only about 4 write operations, or at least
that is what I am seeing with GCC 6.2 as the flags, LRU poitners, and
count/mapcount seem to be cancelling out at least 4 of the 8 assignments on
my system.

One change I had to make to the function was to reduce the minimum page
size to 56 to support some powerpc64 configurations.

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
arch/sparc/include/asm/pgtable_64.h | 30 ------------------------------
include/linux/mm.h | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 34 insertions(+), 30 deletions(-)

diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index 1393a8ac596b..22500c3be7a9 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -231,36 +231,6 @@
extern struct page *mem_map_zero;
#define ZERO_PAGE(vaddr) (mem_map_zero)

-/* This macro must be updated when the size of struct page grows above 80
- * or reduces below 64.
- * The idea that compiler optimizes out switch() statement, and only
- * leaves clrx instructions
- */
-#define mm_zero_struct_page(pp) do { \
- unsigned long *_pp = (void *)(pp); \
- \
- /* Check that struct page is either 64, 72, or 80 bytes */ \
- BUILD_BUG_ON(sizeof(struct page) & 7); \
- BUILD_BUG_ON(sizeof(struct page) < 64); \
- BUILD_BUG_ON(sizeof(struct page) > 80); \
- \
- switch (sizeof(struct page)) { \
- case 80: \
- _pp[9] = 0; /* fallthrough */ \
- case 72: \
- _pp[8] = 0; /* fallthrough */ \
- default: \
- _pp[7] = 0; \
- _pp[6] = 0; \
- _pp[5] = 0; \
- _pp[4] = 0; \
- _pp[3] = 0; \
- _pp[2] = 0; \
- _pp[1] = 0; \
- _pp[0] = 0; \
- } \
-} while (0)
-
/* PFNs are real physical page numbers. However, mem_map only begins to record
* per-page information starting at pfn_base. This is to handle systems where
* the first physical page in the machine is at some huge physical address,
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bb0de406f8e7..ec6e57a0c14e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -102,8 +102,42 @@ static inline void set_max_mapnr(unsigned long limit) { }
* zeroing by defining this macro in <asm/pgtable.h>.
*/
#ifndef mm_zero_struct_page
+#if BITS_PER_LONG == 64
+/* This function must be updated when the size of struct page grows above 80
+ * or reduces below 64. The idea that compiler optimizes out switch()
+ * statement, and only leaves move/store instructions
+ */
+#define mm_zero_struct_page(pp) __mm_zero_struct_page(pp)
+static inline void __mm_zero_struct_page(struct page *page)
+{
+ unsigned long *_pp = (void *)page;
+
+ /* Check that struct page is either 56, 64, 72, or 80 bytes */
+ BUILD_BUG_ON(sizeof(struct page) & 7);
+ BUILD_BUG_ON(sizeof(struct page) < 56);
+ BUILD_BUG_ON(sizeof(struct page) > 80);
+
+ switch (sizeof(struct page)) {
+ case 80:
+ _pp[9] = 0; /* fallthrough */
+ case 72:
+ _pp[8] = 0; /* fallthrough */
+ default:
+ _pp[7] = 0; /* fallthrough */
+ case 56:
+ _pp[6] = 0;
+ _pp[5] = 0;
+ _pp[4] = 0;
+ _pp[3] = 0;
+ _pp[2] = 0;
+ _pp[1] = 0;
+ _pp[0] = 0;
+ }
+}
+#else
#define mm_zero_struct_page(pp) ((void)memset((pp), 0, sizeof(struct page)))
#endif
+#endif

/*
* Default maximum number of active map areas, this limits the number of vmas
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