mm: fold page->_last_nid into page->flags where possible

page->_last_nid fits into page->flags on 64-bit.  The unlikely 32-bit
NUMA configuration with NUMA Balancing will still need an extra page
field.  As Peter notes "Completely dropping 32bit support for
CONFIG_NUMA_BALANCING would simplify things, but it would also remove
the warning if we grow enough 64bit only page-flags to push the last-cpu
out."

[mgorman@suse.de: minor modifications]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Simon Jeons <simon.jeons@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 32 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c2d7d5993b14..473abbda942e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -581,10 +581,11 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
  * sets it, so none of the operations on it need to be atomic.
  */
 
-/* Page flags: | [SECTION] | [NODE] | ZONE | ... | FLAGS | */
+/* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_NID] | ... | FLAGS | */
 #define SECTIONS_PGOFF          ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
 #define NODES_PGOFF             (SECTIONS_PGOFF - NODES_WIDTH)
 #define ZONES_PGOFF             (NODES_PGOFF - ZONES_WIDTH)
+#define LAST_NID_PGOFF          (ZONES_PGOFF - LAST_NID_WIDTH)
 
 /*
  * Define the bit shifts to access each section.  For non-existent
@@ -594,6 +595,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 #define SECTIONS_PGSHIFT        (SECTIONS_PGOFF * (SECTIONS_WIDTH != 0))
 #define NODES_PGSHIFT           (NODES_PGOFF * (NODES_WIDTH != 0))
 #define ZONES_PGSHIFT           (ZONES_PGOFF * (ZONES_WIDTH != 0))
+#define LAST_NID_PGSHIFT        (LAST_NID_PGOFF * (LAST_NID_WIDTH != 0))
 
 /* NODE:ZONE or SECTION:ZONE is used to ID a zone for the buddy allocator */
 #ifdef NODE_NOT_IN_PAGE_FLAGS
@@ -615,6 +617,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 #define ZONES_MASK              ((1UL << ZONES_WIDTH) - 1)
 #define NODES_MASK              ((1UL << NODES_WIDTH) - 1)
 #define SECTIONS_MASK           ((1UL << SECTIONS_WIDTH) - 1)
+#define LAST_NID_MASK           ((1UL << LAST_NID_WIDTH) - 1)
 #define ZONEID_MASK             ((1UL << ZONEID_SHIFT) - 1)
 
 static inline enum zone_type page_zonenum(const struct page *page)
@@ -654,6 +657,7 @@ static inline int page_to_nid(const struct page *page)
 #endif
 
 #ifdef CONFIG_NUMA_BALANCING
+#ifdef LAST_NID_NOT_IN_PAGE_FLAGS
 static inline int page_xchg_last_nid(struct page *page, int nid)
 {
         return xchg(&page->_last_nid, nid);
@@ -668,6 +672,33 @@ static inline void reset_page_last_nid(struct page *page)
         page->_last_nid = -1;
 }
 #else
+static inline int page_last_nid(struct page *page)
+{
+        return (page->flags >> LAST_NID_PGSHIFT) & LAST_NID_MASK;
+}
+
+static inline int page_xchg_last_nid(struct page *page, int nid)
+{
+        unsigned long old_flags, flags;
+        int last_nid;
+
+        do {
+                old_flags = flags = page->flags;
+                last_nid = page_last_nid(page);
+
+                flags &= ~(LAST_NID_MASK << LAST_NID_PGSHIFT);
+                flags |= (nid & LAST_NID_MASK) << LAST_NID_PGSHIFT;
+        } while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));
+
+        return last_nid;
+}
+
+static inline void reset_page_last_nid(struct page *page)
+{
+        page_xchg_last_nid(page, (1 << LAST_NID_SHIFT) - 1);
+}
+#endif /* LAST_NID_NOT_IN_PAGE_FLAGS */
+#else
 static inline int page_xchg_last_nid(struct page *page, int nid)
 {
         return page_to_nid(page);