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Decreasing the size of radix_tree_node #242

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Decreasing the size of radix_tree_node #242

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4654af4
Decreasing the size of radix_tree_node
mzer0-yu Jan 9, 2016
2f150ef
Update radix-tree.h
mzer0-yu Jan 9, 2016
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26 changes: 24 additions & 2 deletions include/linux/radix-tree.h
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Original file line number Diff line number Diff line change
Expand Up @@ -76,17 +76,39 @@ static inline int radix_tree_is_indirect_ptr(void *ptr)
#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
RADIX_TREE_MAP_SHIFT))

/* log2(RADIX_TREE_INDEX_BITS) will not above 10. */
#if sizeof(unsigned long) == 16
#define RADIX_TREE_INDEX_BITS_LOG2 (4 + 3)
#elif sizeof(unsigned long) == 32
#define RADIX_TREE_INDEX_BITS_LOG2 (5 + 3)
#elif sizeof(unsigned long) == 64
#define RADIX_TREE_INDEX_BITS_LOG2 (6 + 3)
#elif sizeof(unsigned long) == 128
#define RADIX_TREE_INDEX_BITS_LOG2 (7 + 3)
#endif
/* log2(RADIX_TREE_MAX_PATH) will not above 9. */
#if RADIX_TREE_MAP_SHIFT == 6
#define RADIX_TREE_MAX_PATH_LOG2 (RADIX_TREE_INDEX_BITS_LOG2 - 2)
#else
#define RADIX_TREE_MAX_PATH_LOG2 (RADIX_TREE_INDEX_BITS_LOG2 - 1)
#endif

/* Height component in node->path */
#define RADIX_TREE_HEIGHT_SHIFT (RADIX_TREE_MAX_PATH + 1)
#define RADIX_TREE_HEIGHT_SHIFT (RADIX_TREE_MAX_PATH_LOG2 + 1)
#define RADIX_TREE_HEIGHT_MASK ((1UL << RADIX_TREE_HEIGHT_SHIFT) - 1)

/* Internally used bits of node->count */
#define RADIX_TREE_COUNT_SHIFT (RADIX_TREE_MAP_SHIFT + 1)
#define RADIX_TREE_COUNT_MASK ((1UL << RADIX_TREE_COUNT_SHIFT) - 1)

/*
* The number of bits of height and offset will not above 12, which is only
* achieved in case of sizeof(unsigned long) == 16 and RADIX_TREE_MAP_SHIFT == 6.
* So unsigned short is enough to store them two, which has 18 bits at least.
*/
struct radix_tree_node {
unsigned int path; /* Offset in parent & height from the bottom */
unsigned int count;
unsigned short path; /* Offset in parent & height from the bottom */
union {
struct {
/* Used when ascending tree */
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