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Remove rtree leading 0 bit optimization.

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A subsequent change instead ignores insignificant high bits.
This commit is contained in:
Jason Evans
2017-02-04 23:08:48 -08:00
parent cdc240d501
commit ff4db5014e
2 changed files with 16 additions and 84 deletions
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35
include/jemalloc/internal/rtree_structs.h
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@@ -19,32 +19,6 @@ struct rtree_elm_witness_tsd_s {
};
struct rtree_level_s {
/*
* A non-NULL subtree points to a subtree rooted along the hypothetical
* path to the leaf node corresponding to key 0. Depending on what keys
* have been used to store to the tree, an arbitrary combination of
* subtree pointers may remain NULL.
*
* Suppose keys comprise 48 bits, and LG_RTREE_BITS_PER_LEVEL is 4.
* This results in a 3-level tree, and the leftmost leaf can be directly
* accessed via levels[2], the subtree prefixed by 0x0000 (excluding
* 0x00000000) can be accessed via levels[1], and the remainder of the
* tree can be accessed via levels[0].
*
* levels[0] : [<unused> | 0x0001******** | 0x0002******** | ...]
*
* levels[1] : [<unused> | 0x00000001**** | 0x00000002**** | ... ]
*
* levels[2] : [extent(0x000000000000) | extent(0x000000000001) | ...]
*
* This has practical implications on x64, which currently uses only the
* lower 47 bits of virtual address space in userland, thus leaving
* levels[0] unused and avoiding a level of tree traversal.
*/
union {
void *subtree_pun;
rtree_elm_t *subtree;
};
/* Number of key bits distinguished by this level. */
unsigned bits;
/*
@@ -68,11 +42,10 @@ struct rtree_ctx_s {
struct rtree_s {
unsigned height;
/*
* Precomputed table used to convert from the number of leading 0 key
* bits to which subtree level to start at.
*/
unsigned start_level[RTREE_HEIGHT_MAX + 1];
union {
void *root_pun;
rtree_elm_t *root;
};
rtree_level_t levels[RTREE_HEIGHT_MAX];
malloc_mutex_t init_lock;
};