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Improve XPath allocator performance

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When allocating new pages, make sure that the page has at least 1/4 of the
base page size free. This makes sure that we can do small allocations after
big allocations (i.e. huge node lists) without doing a heap alloc.

This is important because XPath stack code always reclaims extra pages after
evaluating sub-expressions, so allocating a small chunk of memory and then
rolling the state back is a common case (filtering a node list using a
predicate usually does this).

A better solution involves smarter allocation rollback strategy, but the
implemented solution is simple and practical.

git-svn-id: https://pugixml.googlecode.com/svn/trunk@999 99668b35-9821-0410-8761-19e4c4f06640
This commit is contained in:
Arseny Kapoulkine 2014-06-01 19:12:36 +00:00
parent 6d43ad2870
commit 757c494340
2 changed files with 13 additions and 7 deletions
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16
src/pugixml.cpp
View File

@ -6069,6 +6069,7 @@ PUGI__NS_BEGIN
struct xpath_memory_block struct xpath_memory_block
{ {
xpath_memory_block* next; xpath_memory_block* next;
size_t capacity;
char data[ char data[
#ifdef PUGIXML_MEMORY_XPATH_PAGE_SIZE #ifdef PUGIXML_MEMORY_XPATH_PAGE_SIZE
@ -6098,12 +6099,10 @@ PUGI__NS_BEGIN
void* allocate_nothrow(size_t size) void* allocate_nothrow(size_t size)
{ {
const size_t block_capacity = sizeof(_root->data);
// align size so that we're able to store pointers in subsequent blocks // align size so that we're able to store pointers in subsequent blocks
size = (size + sizeof(void*) - 1) & ~(sizeof(void*) - 1); size = (size + sizeof(void*) - 1) & ~(sizeof(void*) - 1);
if (_root_size + size <= block_capacity) if (_root_size + size <= _root->capacity)
{ {
void* buf = _root->data + _root_size; void* buf = _root->data + _root_size;
_root_size += size; _root_size += size;
@ -6111,13 +6110,18 @@ PUGI__NS_BEGIN
} }
else else
{ {
size_t block_data_size = (size > block_capacity) ? size : block_capacity; // make sure we have at least 1/4th of the page free after allocation to satisfy subsequent allocation requests
size_t block_size = block_data_size + offsetof(xpath_memory_block, data); size_t block_capacity_base = sizeof(_root->data);
size_t block_capacity_req = size + block_capacity_base / 4;
size_t block_capacity = (block_capacity_base > block_capacity_req) ? block_capacity_base : block_capacity_req;
size_t block_size = block_capacity + offsetof(xpath_memory_block, data);
xpath_memory_block* block = static_cast<xpath_memory_block*>(xml_memory::allocate(block_size)); xpath_memory_block* block = static_cast<xpath_memory_block*>(xml_memory::allocate(block_size));
if (!block) return 0; if (!block) return 0;
block->next = _root; block->next = _root;
block->capacity = block_capacity;
_root = block; _root = block;
_root_size = size; _root_size = size;
@ -6258,6 +6262,7 @@ PUGI__NS_BEGIN
xpath_stack_data(): result(blocks + 0), temp(blocks + 1) xpath_stack_data(): result(blocks + 0), temp(blocks + 1)
{ {
blocks[0].next = blocks[1].next = 0; blocks[0].next = blocks[1].next = 0;
blocks[0].capacity = blocks[1].capacity = sizeof(blocks[0].data);
stack.result = &result; stack.result = &result;
stack.temp = &temp; stack.temp = &temp;
@ -9990,6 +9995,7 @@ PUGI__NS_BEGIN
xpath_query_impl(): root(0), alloc(&block) xpath_query_impl(): root(0), alloc(&block)
{ {
block.next = 0; block.next = 0;
block.capacity = sizeof(block.data);
} }
xpath_ast_node* root; xpath_ast_node* root;

4
tests/test_xpath.cpp
View File

@ -328,7 +328,7 @@ TEST(xpath_large_node_set)
TEST(xpath_out_of_memory_evaluate_concat) TEST(xpath_out_of_memory_evaluate_concat)
{ {
test_runner::_memory_fail_threshold = 4096 * 2 * sizeof(char_t) + 4096 * 2; test_runner::_memory_fail_threshold = 4196 * sizeof(char_t) + 4096 * 2;
std::basic_string<char_t> query = STR("concat(\"a\", \""); std::basic_string<char_t> query = STR("concat(\"a\", \"");
@ -354,7 +354,7 @@ TEST(xpath_out_of_memory_evaluate_concat)
TEST(xpath_out_of_memory_evaluate_substring) TEST(xpath_out_of_memory_evaluate_substring)
{ {
test_runner::_memory_fail_threshold = 4096 * 2 * sizeof(char_t) + 4096 * 2; test_runner::_memory_fail_threshold = 4196 * sizeof(char_t) + 4096 * 2;
std::basic_string<char_t> query = STR("substring(\""); std::basic_string<char_t> query = STR("substring(\"");