From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
We're already using a union of many fields here, so stop abusing the
_map_count and make page_type its own field. That implies renaming some
of the machinery that creates PageBuddy, PageBalloon and PageKmemcg;
bring back the PG_buddy, PG_balloon and PG_kmemcg names. Also, the
special values don't need to be (and probably shouldn't be) powers of two,
so renumber them to just start at -128.
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
---
include/linux/mm_types.h | 13 ++++++++-----
include/linux/page-flags.h | 36 +++++++++++++++++-------------------
2 files changed, 25 insertions(+), 24 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fd1af6b9591d..1c5dea402501 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -94,6 +94,14 @@ struct page {
};
union {
+ /*
+ * If the page is neither PageSlab nor PageAnon, the value
+ * stored here may help distinguish it from page cache pages.
+ * See page-flags.h for a list of page types which are
+ * currently stored here.
+ */
+ unsigned int page_type;
+
_slub_counter_t counters;
unsigned int active; /* SLAB */
struct { /* SLUB */
@@ -107,11 +115,6 @@ struct page {
/*
* 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;
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 50c2b8786831..ba6a7e883425 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -630,49 +630,47 @@ PAGEFLAG_FALSE(DoubleMap)
#endif
/*
- * For pages that are never mapped to userspace, page->mapcount may be
- * used for storing extra information about page type. Any value used
- * for this purpose must be <= -2, but it's better start not too close
- * to -2 so that an underflow of the page_mapcount() won't be mistaken
- * for a special page.
+ * For pages that are never mapped to userspace, page_type may be
+ * used. Values used for this purpose must be <= -2, but we leave a gap
+ * so that an underflow of page_mapcount() won't be mistaken for a
+ * special page.
*/
-#define PAGE_MAPCOUNT_OPS(uname, lname) \
+#define PAGE_TYPE_OPS(uname, lname) \
static __always_inline int Page##uname(struct page *page) \
{ \
- return atomic_read(&page->_mapcount) == \
- PAGE_##lname##_MAPCOUNT_VALUE; \
+ return page->page_type == PG_##lname; \
} \
static __always_inline void __SetPage##uname(struct page *page) \
{ \
- VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page); \
- atomic_set(&page->_mapcount, PAGE_##lname##_MAPCOUNT_VALUE); \
+ VM_BUG_ON_PAGE(page->page_type != -1, page); \
+ page->page_type = PG_##lname; \
} \
static __always_inline void __ClearPage##uname(struct page *page) \
{ \
VM_BUG_ON_PAGE(!Page##uname(page), page); \
- atomic_set(&page->_mapcount, -1); \
+ page->page_type = -1; \
}
/*
- * PageBuddy() indicate that the page is free and in the buddy system
+ * PageBuddy() indicates that the page is free and in the buddy system
* (see mm/page_alloc.c).
*/
-#define PAGE_BUDDY_MAPCOUNT_VALUE (-128)
-PAGE_MAPCOUNT_OPS(Buddy, BUDDY)
+#define PG_buddy (-128)
+PAGE_TYPE_OPS(Buddy, buddy)
/*
- * PageBalloon() is set on pages that are on the balloon page list
+ * PageBalloon() is true for pages that are on the balloon page list
* (see mm/balloon_compaction.c).
*/
-#define PAGE_BALLOON_MAPCOUNT_VALUE (-256)
-PAGE_MAPCOUNT_OPS(Balloon, BALLOON)
+#define PG_balloon (-129)
+PAGE_TYPE_OPS(Balloon, balloon)
/*
* If kmemcg is enabled, the buddy allocator will set PageKmemcg() on
* pages allocated with __GFP_ACCOUNT. It gets cleared on page free.
*/
-#define PAGE_KMEMCG_MAPCOUNT_VALUE (-512)
-PAGE_MAPCOUNT_OPS(Kmemcg, KMEMCG)
+#define PG_kmemcg (-130)
+PAGE_TYPE_OPS(Kmemcg, kmemcg)
extern bool is_free_buddy_page(struct page *page);
--
2.15.1
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