[PATCH v5 04/17] mm: Switch s_mem and slab_cache in struct page

[Matthew Wilcox <willy@infradead.org>]

From: Matthew Wilcox <mawilcox@microsoft.com>

This will allow us to store slub's counters in the same bits as slab's
s_mem.  slub now needs to set page->mapping to NULL as it frees the page,
just like slab does.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 include/linux/mm_types.h | 4 ++--
 mm/slub.c                | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 41828fb34860..e97a310a6abe 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -83,7 +83,7 @@ struct page {
 		/* See page-flags.h for the definition of PAGE_MAPPING_FLAGS */
 		struct address_space *mapping;
 
-		void *s_mem;			/* slab first object */
+		struct kmem_cache *slab_cache;	/* SL[AU]B: Pointer to slab */
 		atomic_t compound_mapcount;	/* first tail page */
 		/* page_deferred_list().next	 -- second tail page */
 	};
@@ -194,7 +194,7 @@ struct page {
 		spinlock_t ptl;
 #endif
 #endif
-		struct kmem_cache *slab_cache;	/* SL[AU]B: Pointer to slab */
+		void *s_mem;			/* slab first object */
 	};
 
 #ifdef CONFIG_MEMCG
diff --git a/mm/slub.c b/mm/slub.c
index e938184ac847..7fc13c46e975 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1690,6 +1690,7 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
 	__ClearPageSlab(page);
 
 	page_mapcount_reset(page);
+	page->mapping = NULL;
 	if (current->reclaim_state)
 		current->reclaim_state->reclaimed_slab += pages;
 	memcg_uncharge_slab(page, order, s);
-- 
2.17.0