From: Matthew Wilcox <mawil...@microsoft.com>

None of these four bits may be used for slab allocations, so we can
use them for flags as long as we mask them off before passing them
to the slab allocator.  Move the IDR flag from the top bits to the
bottom bits.

Signed-off-by: Matthew Wilcox <mawil...@microsoft.com>
---
 include/linux/idr.h                  | 3 ++-
 include/linux/radix-tree.h           | 7 ++++---
 lib/radix-tree.c                     | 3 ++-
 tools/testing/radix-tree/linux/gfp.h | 1 +
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 7d6a6313f0ab..913c335054f0 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -29,7 +29,8 @@ struct idr {
 #define IDR_FREE       0
 
 /* Set the IDR flag and the IDR_FREE tag */
-#define IDR_RT_MARKER          ((__force gfp_t)(3 << __GFP_BITS_SHIFT))
+#define IDR_RT_MARKER  (ROOT_IS_IDR | (__force gfp_t)                  \
+                                       (1 << (ROOT_TAG_SHIFT + IDR_FREE)))
 
 #define IDR_INIT_BASE(base) {                                          \
        .idr_rt = RADIX_TREE_INIT(IDR_RT_MARKER),                       \
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index fc55ff31eca7..6c4e2e716dac 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -104,9 +104,10 @@ struct radix_tree_node {
        unsigned long   tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
 };
 
-/* The top bits of gfp_mask are used to store the root tags and the IDR flag */
-#define ROOT_IS_IDR    ((__force gfp_t)(1 << __GFP_BITS_SHIFT))
-#define ROOT_TAG_SHIFT (__GFP_BITS_SHIFT + 1)
+/* The IDR tag is stored in the low bits of the GFP flags */
+#define ROOT_IS_IDR    ((__force gfp_t)4)
+/* The top bits of gfp_mask are used to store the root tags */
+#define ROOT_TAG_SHIFT (__GFP_BITS_SHIFT)
 
 struct radix_tree_root {
        gfp_t                   gfp_mask;
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 0a7ae3288a24..66732e2f9606 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -146,7 +146,7 @@ static unsigned int radix_tree_descend(const struct 
radix_tree_node *parent,
 
 static inline gfp_t root_gfp_mask(const struct radix_tree_root *root)
 {
-       return root->gfp_mask & __GFP_BITS_MASK;
+       return root->gfp_mask & ((__GFP_BITS_MASK >> 4) << 4);
 }
 
 static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
@@ -2285,6 +2285,7 @@ void __init radix_tree_init(void)
        int ret;
 
        BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
+       BUILD_BUG_ON(GFP_ZONEMASK != (__force gfp_t)15);
        radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
                        sizeof(struct radix_tree_node), 0,
                        SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
diff --git a/tools/testing/radix-tree/linux/gfp.h 
b/tools/testing/radix-tree/linux/gfp.h
index e9fff59dfd8a..a72007d9818b 100644
--- a/tools/testing/radix-tree/linux/gfp.h
+++ b/tools/testing/radix-tree/linux/gfp.h
@@ -18,6 +18,7 @@
 
 #define __GFP_RECLAIM  (__GFP_DIRECT_RECLAIM|__GFP_KSWAPD_RECLAIM)
 
+#define GFP_ZONEMASK   0x0fu
 #define GFP_ATOMIC     (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
 #define GFP_KERNEL     (__GFP_RECLAIM | __GFP_IO | __GFP_FS)
 #define GFP_NOWAIT     (__GFP_KSWAPD_RECLAIM)
-- 
2.16.1

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