[PATCH v2 mmotm 1/3] mm, page_alloc: add unlikely macro to help compiler optimization

[PATCH v2 mmotm 1/3] mm, page_alloc: add unlikely macro to help compiler optimization

[Joonsoo Kim]

We rarely allocate a page with ALLOC_NO_WATERMARKS and it is used
in slow path. For helping compiler optimization, add unlikely macro to
ALLOC_NO_WATERMARKS checking.

This patch doesn't have any effect now, because gcc already optimize
this properly. But we cannot assume that gcc always does right and nobody
re-evaluate if gcc do proper optimization with their change, for example,
it is not optimized properly on v3.10. So adding compiler hint here
is reasonable.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f5c549c..04bec49 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1901,7 +1901,7 @@ zonelist_scan:
 			!cpuset_zone_allowed_softwall(zone, gfp_mask))
 				continue;
 		BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
-		if (alloc_flags & ALLOC_NO_WATERMARKS)
+		if (unlikely(alloc_flags & ALLOC_NO_WATERMARKS))
 			goto try_this_zone;
 		/*
 		 * Distribute pages in proportion to the individual
-- 
1.7.9.5

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[PATCH v2 mmotm 2/3] mm: move pgtable related functions to right place

[Joonsoo Kim]

pgtable related functions are mostly in pgtable-generic.c.
So move remaining functions from memory.c to pgtable-generic.c.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/mm/memory.c b/mm/memory.c
index f2ab2a8..8fd4d42 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -374,30 +374,6 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table)
 #endif /* CONFIG_HAVE_RCU_TABLE_FREE */
 
 /*
- * If a p?d_bad entry is found while walking page tables, report
- * the error, before resetting entry to p?d_none.  Usually (but
- * very seldom) called out from the p?d_none_or_clear_bad macros.
- */
-
-void pgd_clear_bad(pgd_t *pgd)
-{
-	pgd_ERROR(*pgd);
-	pgd_clear(pgd);
-}
-
-void pud_clear_bad(pud_t *pud)
-{
-	pud_ERROR(*pud);
-	pud_clear(pud);
-}
-
-void pmd_clear_bad(pmd_t *pmd)
-{
-	pmd_ERROR(*pmd);
-	pmd_clear(pmd);
-}
-
-/*
  * Note: this doesn't free the actual pages themselves. That
  * has been handled earlier when unmapping all the memory regions.
  */
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index e1a6e4f..3929a40 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -10,6 +10,30 @@
 #include <asm/tlb.h>
 #include <asm-generic/pgtable.h>
 
+/*
+ * If a p?d_bad entry is found while walking page tables, report
+ * the error, before resetting entry to p?d_none.  Usually (but
+ * very seldom) called out from the p?d_none_or_clear_bad macros.
+ */
+
+void pgd_clear_bad(pgd_t *pgd)
+{
+	pgd_ERROR(*pgd);
+	pgd_clear(pgd);
+}
+
+void pud_clear_bad(pud_t *pud)
+{
+	pud_ERROR(*pud);
+	pud_clear(pud);
+}
+
+void pmd_clear_bad(pmd_t *pmd)
+{
+	pmd_ERROR(*pmd);
+	pmd_clear(pmd);
+}
+
 #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
 /*
  * Only sets the access flags (dirty, accessed), as well as write 
-- 
1.7.9.5

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[PATCH v2 mmotm 3/3] swap: clean-up #ifdef in page_mapping()

[Joonsoo Kim]

PageSwapCache() is always false when !CONFIG_SWAP, so compiler
properly discard related code. Therefore, we don't need #ifdef explicitly.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 24db914..c03c139 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -447,6 +447,7 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
 
 #else /* CONFIG_SWAP */
 
+#define swap_address_space(entry)		(NULL)
 #define get_nr_swap_pages()			0L
 #define total_swap_pages			0L
 #define total_swapcache_pages()			0UL
diff --git a/mm/util.c b/mm/util.c
index 7441c41..eaf63fc2 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -388,15 +388,12 @@ struct address_space *page_mapping(struct page *page)
 	struct address_space *mapping = page->mapping;
 
 	VM_BUG_ON(PageSlab(page));
-#ifdef CONFIG_SWAP
 	if (unlikely(PageSwapCache(page))) {
 		swp_entry_t entry;
 
 		entry.val = page_private(page);
 		mapping = swap_address_space(entry);
-	} else
-#endif
-	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
+	} else if ((unsigned long)mapping & PAGE_MAPPING_ANON)
 		mapping = NULL;
 	return mapping;
 }
-- 
1.7.9.5

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