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Replace rtree path cache with LRU cache.

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Rework rtree_ctx_t to encapsulate an rtree leaf LRU lookup cache rather
than a single-path element lookup cache.  The replacement is logically
much simpler, as well as slightly faster in the fast path case and less
prone to degraded performance during non-trivial sequences of lookups.
This commit is contained in:
Jason Evans 2017-02-03 20:21:56 -08:00
parent 0ecf692726
commit 4a346f5593
4 changed files with 107 additions and 123 deletions
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2
include/jemalloc/internal/private_symbols.txt
View File

@ -419,7 +419,6 @@ rtree_child_read
rtree_child_read_hard
rtree_child_tryread
rtree_clear
rtree_ctx_start_level
rtree_delete
rtree_elm_acquire
rtree_elm_lookup
@ -431,6 +430,7 @@ rtree_elm_witness_acquire
rtree_elm_witness_release
rtree_elm_write
rtree_elm_write_acquired
rtree_leafkey
rtree_new
rtree_node_alloc
rtree_node_dalloc

166
include/jemalloc/internal/rtree_inlines.h
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@ -3,8 +3,7 @@
#ifndef JEMALLOC_ENABLE_INLINE
unsigned rtree_start_level(const rtree_t *rtree, uintptr_t key);
unsigned rtree_ctx_start_level(const rtree_t *rtree,
const rtree_ctx_t *rtree_ctx, uintptr_t key);
uintptr_t rtree_leafkey(rtree_t *rtree, uintptr_t key);
uintptr_t rtree_subkey(rtree_t *rtree, uintptr_t key, unsigned level);
bool rtree_node_valid(rtree_elm_t *node);
@ -50,31 +49,24 @@ rtree_start_level(const rtree_t *rtree, uintptr_t key) {
return start_level;
}
JEMALLOC_ALWAYS_INLINE unsigned
rtree_ctx_start_level(const rtree_t *rtree, const rtree_ctx_t *rtree_ctx,
uintptr_t key) {
unsigned start_level;
uintptr_t key_diff;
/* Compute the difference between old and new lookup keys. */
key_diff = key ^ rtree_ctx->key;
assert(key_diff != 0); /* Handled in rtree_elm_lookup(). */
/*
* Compute the last traversal path element at which the keys' paths
* are the same.
*/
start_level = rtree->start_level[(lg_floor(key_diff) + 1) >>
LG_RTREE_BITS_PER_LEVEL];
assert(start_level < rtree->height);
return start_level;
JEMALLOC_ALWAYS_INLINE uintptr_t
rtree_leafkey(rtree_t *rtree, uintptr_t key) {
unsigned ptrbits = ZU(1) << (LG_SIZEOF_PTR+3);
unsigned cumbits = (rtree->levels[rtree->height-1].cumbits -
rtree->levels[rtree->height-1].bits);
unsigned maskbits = ptrbits - cumbits;
uintptr_t mask = ~((ZU(1) << maskbits) - 1);
return (key & mask);
}
JEMALLOC_ALWAYS_INLINE uintptr_t
rtree_subkey(rtree_t *rtree, uintptr_t key, unsigned level) {
return ((key >> ((ZU(1) << (LG_SIZEOF_PTR+3)) -
rtree->levels[level].cumbits)) & ((ZU(1) <<
rtree->levels[level].bits) - 1));
unsigned ptrbits = ZU(1) << (LG_SIZEOF_PTR+3);
unsigned cumbits = rtree->levels[level].cumbits;
unsigned shiftbits = ptrbits - cumbits;
unsigned maskbits = rtree->levels[level].bits;
unsigned mask = (ZU(1) << maskbits) - 1;
return ((key >> shiftbits) & mask);
}
JEMALLOC_ALWAYS_INLINE bool
@ -170,103 +162,89 @@ rtree_subtree_read(tsdn_t *tsdn, rtree_t *rtree, unsigned level,
JEMALLOC_ALWAYS_INLINE rtree_elm_t *
rtree_elm_lookup(tsdn_t *tsdn, rtree_t *rtree, rtree_ctx_t *rtree_ctx,
uintptr_t key, bool dependent, bool init_missing) {
uintptr_t subkey;
unsigned start_level;
rtree_elm_t *node;
assert(!dependent || !init_missing);
if (dependent || init_missing) {
if (likely(rtree_ctx->valid)) {
if (key == rtree_ctx->key) {
return rtree_ctx->elms[rtree->height];
} else {
unsigned no_ctx_start_level =
rtree_start_level(rtree, key);
unsigned ctx_start_level;
if (likely(no_ctx_start_level <=
rtree_ctx->start_level && (ctx_start_level =
rtree_ctx_start_level(rtree, rtree_ctx,
key)) >= rtree_ctx->start_level)) {
start_level = ctx_start_level;
node = rtree_ctx->elms[ctx_start_level];
} else {
start_level = no_ctx_start_level;
node = init_missing ?
rtree_subtree_read(tsdn, rtree,
no_ctx_start_level, dependent) :
rtree_subtree_tryread(rtree,
no_ctx_start_level, dependent);
rtree_ctx->start_level =
no_ctx_start_level;
rtree_ctx->elms[no_ctx_start_level] =
node;
/* Search the cache. */
uintptr_t leafkey = rtree_leafkey(rtree, key);
if (likely(key != 0)) {
#define RTREE_CACHE_CHECK(i) do { \
if (likely(rtree_ctx->cache[i].leafkey == leafkey)) { \
rtree_elm_t *leaf = rtree_ctx->cache[i].leaf; \
if (likely(leaf != NULL)) { \
/* Reorder. */ \
memmove(&rtree_ctx->cache[1], \
&rtree_ctx->cache[0], \
sizeof(rtree_ctx_cache_elm_t) * i); \
rtree_ctx->cache[0].leafkey = leafkey; \
rtree_ctx->cache[0].leaf = leaf; \
\
uintptr_t subkey = rtree_subkey(rtree, \
key, rtree->height-1); \
return &leaf[subkey]; \
} \
} \
} while (0)
/* Check the MRU cache entry. */
RTREE_CACHE_CHECK(0);
/*
* Search the remaining cache elements, and on success move the
* matching element to the front. Unroll the first iteration to
* avoid calling memmove() (the compiler typically optimizes it
* into raw moves).
*/
if (RTREE_CTX_NCACHE > 1) {
RTREE_CACHE_CHECK(1);
}
for (unsigned i = 2; i < RTREE_CTX_NCACHE; i++) {
RTREE_CACHE_CHECK(i);
}
#undef RTREE_CACHE_CHECK
}
} else {
unsigned no_ctx_start_level = rtree_start_level(rtree,
key);
start_level = no_ctx_start_level;
node = init_missing ? rtree_subtree_read(tsdn, rtree,
no_ctx_start_level, dependent) :
rtree_subtree_tryread(rtree, no_ctx_start_level,
unsigned start_level = rtree_start_level(rtree, key);
rtree_elm_t *node = init_missing ? rtree_subtree_read(tsdn, rtree,
start_level, dependent) : rtree_subtree_tryread(rtree, start_level,
dependent);
rtree_ctx->valid = true;
rtree_ctx->start_level = no_ctx_start_level;
rtree_ctx->elms[no_ctx_start_level] = node;
}
rtree_ctx->key = key;
} else {
start_level = rtree_start_level(rtree, key);
node = init_missing ? rtree_subtree_read(tsdn, rtree,
start_level, dependent) : rtree_subtree_tryread(rtree,
start_level, dependent);
}
#define RTREE_GET_BIAS (RTREE_HEIGHT_MAX - rtree->height)
switch (start_level + RTREE_GET_BIAS) {
#define RTREE_GET_SUBTREE(level) \
case level: \
case level: { \
assert(level < (RTREE_HEIGHT_MAX-1)); \
if (!dependent && unlikely(!rtree_node_valid(node))) { \
if (init_missing) { \
rtree_ctx->valid = false; \
} \
return NULL; \
} \
subkey = rtree_subkey(rtree, key, level - \
uintptr_t subkey = rtree_subkey(rtree, key, level - \
RTREE_GET_BIAS); \
node = init_missing ? rtree_child_read(tsdn, rtree, \
&node[subkey], level - RTREE_GET_BIAS, dependent) : \
rtree_child_tryread(&node[subkey], dependent); \
if (dependent || init_missing) { \
rtree_ctx->elms[level - RTREE_GET_BIAS + 1] = \
node; \
} \
/* Fall through. */
/* Fall through. */ \
}
#define RTREE_GET_LEAF(level) \
case level: \
case level: { \
assert(level == (RTREE_HEIGHT_MAX-1)); \
if (!dependent && unlikely(!rtree_node_valid(node))) { \
if (init_missing) { \
rtree_ctx->valid = false; \
} \
return NULL; \
} \
subkey = rtree_subkey(rtree, key, level - \
RTREE_GET_BIAS); \
/* \
* node is a leaf, so it contains values rather than \
* child pointers. \
*/ \
node = &node[subkey]; \
if (dependent || init_missing) { \
rtree_ctx->elms[level - RTREE_GET_BIAS + 1] = \
node; \
if (likely(key != 0)) { \
if (RTREE_CTX_NCACHE > 1) { \
memmove(&rtree_ctx->cache[1], \
&rtree_ctx->cache[0], \
sizeof(rtree_ctx_cache_elm_t) * \
(RTREE_CTX_NCACHE-1)); \
} \
return node;
rtree_ctx->cache[0].leafkey = leafkey; \
rtree_ctx->cache[0].leaf = node; \
} \
uintptr_t subkey = rtree_subkey(rtree, key, level - \
RTREE_GET_BIAS); \
return &node[subkey]; \
}
#if RTREE_HEIGHT_MAX > 1
RTREE_GET_SUBTREE(0)
#endif
@ -365,16 +343,14 @@ rtree_elm_acquire(tsdn_t *tsdn, rtree_t *rtree, rtree_ctx_t *rtree_ctx,
if (!dependent && elm == NULL) {
return NULL;
}
{
extent_t *extent;
void *s;
do {
extent = rtree_elm_read(elm, false);
/* The least significant bit serves as a lock. */
s = (void *)((uintptr_t)extent | (uintptr_t)0x1);
} while (atomic_cas_p(&elm->pun, (void *)extent, s));
}
if (config_debug) {
rtree_elm_witness_acquire(tsdn, rtree, key, elm);

24
include/jemalloc/internal/rtree_structs.h
View File

@ -54,22 +54,16 @@ struct rtree_level_s {
unsigned cumbits;
};
struct rtree_ctx_cache_elm_s {
uintptr_t leafkey;
rtree_elm_t *leaf;
};
struct rtree_ctx_s {
/* If false, key/elms have not yet been initialized by a lookup. */
bool valid;
/* Key that corresponds to the tree path recorded in elms. */
uintptr_t key;
/* Memoized rtree_start_level(key). */
unsigned start_level;
/*
* A path through rtree, driven by key. Only elements that could
* actually be used for subsequent lookups are initialized, i.e. if
* start_level = rtree_start_level(key) is non-zero, the first
* start_level elements are uninitialized. The last element contains a
* pointer to the leaf node element that corresponds to key, so that
* exact matches require no tree node offset computation.
*/
rtree_elm_t *elms[RTREE_HEIGHT_MAX + 1];
#ifndef _MSC_VER
JEMALLOC_ALIGNED(CACHELINE)
#endif
rtree_ctx_cache_elm_t cache[RTREE_CTX_NCACHE];
};
struct rtree_s {

22
include/jemalloc/internal/rtree_types.h
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@ -12,6 +12,7 @@ typedef struct rtree_elm_s rtree_elm_t;
typedef struct rtree_elm_witness_s rtree_elm_witness_t;
typedef struct rtree_elm_witness_tsd_s rtree_elm_witness_tsd_t;
typedef struct rtree_level_s rtree_level_t;
typedef struct rtree_ctx_cache_elm_s rtree_ctx_cache_elm_t;
typedef struct rtree_ctx_s rtree_ctx_t;
typedef struct rtree_s rtree_t;
@ -25,11 +26,24 @@ typedef struct rtree_s rtree_t;
#define RTREE_HEIGHT_MAX \
((1U << (LG_SIZEOF_PTR+3)) / RTREE_BITS_PER_LEVEL)
/*
* Number of leafkey/leaf pairs to cache. Each entry supports an entire leaf,
* so the cache hit rate is typically high even with a small number of entries.
* In rare cases extent activity will straddle the boundary between two leaf
* nodes. Furthermore, an arena may use a combination of dss and mmap. Four
* entries covers both of these considerations as long as locality of reference
* is high, and/or total memory usage doesn't exceed the range supported by
* those entries. Note that as memory usage grows past the amount that this
* cache can directly cover, the cache will become less effective if locality of
* reference is low, but the consequence is merely cache misses while traversing
* the tree nodes, and the cache will itself suffer cache misses if made overly
* large, not to mention the cost of linear search.
*/
#define RTREE_CTX_NCACHE 8
/* Static initializer for rtree_ctx_t. */
#define RTREE_CTX_INITIALIZER { \
false, \
0, \
0, \
{NULL /* C initializes all trailing elements to NULL. */} \
{{0, NULL} /* C initializes all trailing elements to NULL. */} \
}
/*