8231460: Performance issue (CodeHeap) with large free blocks
Reviewed-by: adinn, stuefe
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
#include "precompiled.hpp"
#include "memory/heap.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/os.hpp"
#include "services/memTracker.hpp"
#include "utilities/align.hpp"
size_t CodeHeap::header_size() {
return sizeof(HeapBlock);
}
// Implementation of Heap
CodeHeap::CodeHeap(const char* name, const int code_blob_type)
: _code_blob_type(code_blob_type) {
_name = name;
_number_of_committed_segments = 0;
_number_of_reserved_segments = 0;
_segment_size = 0;
_log2_segment_size = 0;
_next_segment = 0;
_freelist = NULL;
_last_insert_point = NULL;
_freelist_segments = 0;
_freelist_length = 0;
_max_allocated_capacity = 0;
_blob_count = 0;
_nmethod_count = 0;
_adapter_count = 0;
_full_count = 0;
_fragmentation_count = 0;
}
// Dummy initialization of template array.
char CodeHeap::segmap_template[] = {0};
// This template array is used to (re)initialize the segmap,
// replacing a 1..254 loop.
void CodeHeap::init_segmap_template() {
assert(free_sentinel == 255, "Segment map logic changed!");
for (int i = 0; i <= free_sentinel; i++) {
segmap_template[i] = i;
}
}
// The segmap is marked free for that part of the heap
// which has not been allocated yet (beyond _next_segment).
// The range of segments to be marked is given by [beg..end).
// "Allocated" space in this context means there exists a
// HeapBlock or a FreeBlock describing this space.
// This method takes segment map indices as range boundaries
void CodeHeap::mark_segmap_as_free(size_t beg, size_t end) {
assert( beg < _number_of_committed_segments, "interval begin out of bounds");
assert(beg < end && end <= _number_of_committed_segments, "interval end out of bounds");
// Don't do unpredictable things in PRODUCT build
if (beg < end) {
// setup _segmap pointers for faster indexing
address p = (address)_segmap.low() + beg;
address q = (address)_segmap.low() + end;
// initialize interval
memset(p, free_sentinel, q-p);
}
}
// Don't get confused here.
// All existing blocks, no matter if they are used() or free(),
// have their segmap marked as used. This allows to find the
// block header (HeapBlock or FreeBlock) for any pointer
// within the allocated range (upper limit: _next_segment).
// This method takes segment map indices as range boundaries.
// The range of segments to be marked is given by [beg..end).
void CodeHeap::mark_segmap_as_used(size_t beg, size_t end, bool is_FreeBlock_join) {
assert( beg < _number_of_committed_segments, "interval begin out of bounds");
assert(beg < end && end <= _number_of_committed_segments, "interval end out of bounds");
// Don't do unpredictable things in PRODUCT build
if (beg < end) {
// setup _segmap pointers for faster indexing
address p = (address)_segmap.low() + beg;
address q = (address)_segmap.low() + end;
// initialize interval
// If we are joining two free blocks, the segmap range for each
// block is consistent. To create a consistent segmap range for
// the blocks combined, we have three choices:
// 1 - Do a full init from beg to end. Not very efficient because
// the segmap range for the left block is potentially initialized
// over and over again.
// 2 - Carry over the last segmap element value of the left block
// and initialize the segmap range of the right block starting
// with that value. Saves initializing the left block's segmap
// over and over again. Very efficient if FreeBlocks mostly
// are appended to the right.
// 3 - Take full advantage of the segmap being almost correct with
// the two blocks combined. Lets assume the left block consists
// of m segments. The the segmap looks like
// ... (m-2) (m-1) (m) 0 1 2 3 ...
// By substituting the '0' by '1', we create a valid, but
// suboptimal, segmap range covering the two blocks combined.
// We introduced an extra hop for the find_block_for() iteration.
//
// When this method is called with is_FreeBlock_join == true, the
// segmap index beg must select the first segment of the right block.
// Otherwise, it has to select the first segment of the left block.
// Variant 3 is used for all FreeBlock joins.
if (is_FreeBlock_join && (beg > 0)) {
#ifndef PRODUCT
FreeBlock* pBlock = (FreeBlock*)block_at(beg);
assert(beg + pBlock->length() == end, "Internal error: (%d - %d) != %d", (unsigned int)end, (unsigned int)beg, (unsigned int)(pBlock->length()));
assert(*p == 0, "Begin index does not select a block start segment, *p = %2.2x", *p);
#endif
// If possible, extend the previous hop.
if (*(p-1) < (free_sentinel-1)) {
*p = *(p-1) + 1;
} else {
*p = 1;
}
if (_fragmentation_count++ >= fragmentation_limit) {
defrag_segmap(true);
_fragmentation_count = 0;
}
} else {
size_t n_bulk = free_sentinel-1; // bulk processing uses template indices [1..254].
// Use shortcut for blocks <= 255 segments.
// Special case bulk processing: [0..254].
if ((end - beg) <= n_bulk) {
memcpy(p, &segmap_template[0], end - beg);
} else {
*p++ = 0; // block header marker
while (p < q) {
if ((p+n_bulk) <= q) {
memcpy(p, &segmap_template[1], n_bulk);
p += n_bulk;
} else {
memcpy(p, &segmap_template[1], q-p);
p = q;
}
}
}
}
}
}
void CodeHeap::invalidate(size_t beg, size_t end, size_t hdr_size) {
#ifndef PRODUCT
// Fill the given range with some bad value.
// length is expected to be in segment_size units.
// This prevents inadvertent execution of code leftover from previous use.
char* p = low_boundary() + segments_to_size(beg) + hdr_size;
memset(p, badCodeHeapNewVal, segments_to_size(end-beg)-hdr_size);
#endif
}
void CodeHeap::clear(size_t beg, size_t end) {
mark_segmap_as_free(beg, end);
invalidate(beg, end, 0);
}
void CodeHeap::clear() {
_next_segment = 0;
clear(_next_segment, _number_of_committed_segments);
}
static size_t align_to_page_size(size_t size) {
const size_t alignment = (size_t)os::vm_page_size();
assert(is_power_of_2(alignment), "no kidding ???");
return (size + alignment - 1) & ~(alignment - 1);
}
void CodeHeap::on_code_mapping(char* base, size_t size) {
#ifdef LINUX
extern void linux_wrap_code(char* base, size_t size);
linux_wrap_code(base, size);
#endif
}
bool CodeHeap::reserve(ReservedSpace rs, size_t committed_size, size_t segment_size) {
assert(rs.size() >= committed_size, "reserved < committed");
assert(segment_size >= sizeof(FreeBlock), "segment size is too small");
assert(is_power_of_2(segment_size), "segment_size must be a power of 2");
_segment_size = segment_size;
_log2_segment_size = exact_log2(segment_size);
// Reserve and initialize space for _memory.
size_t page_size = os::vm_page_size();
if (os::can_execute_large_page_memory()) {
const size_t min_pages = 8;
page_size = MIN2(os::page_size_for_region_aligned(committed_size, min_pages),
os::page_size_for_region_aligned(rs.size(), min_pages));
}
const size_t granularity = os::vm_allocation_granularity();
const size_t c_size = align_up(committed_size, page_size);
os::trace_page_sizes(_name, committed_size, rs.size(), page_size,
rs.base(), rs.size());
if (!_memory.initialize(rs, c_size)) {
return false;
}
on_code_mapping(_memory.low(), _memory.committed_size());
_number_of_committed_segments = size_to_segments(_memory.committed_size());
_number_of_reserved_segments = size_to_segments(_memory.reserved_size());
assert(_number_of_reserved_segments >= _number_of_committed_segments, "just checking");
const size_t reserved_segments_alignment = MAX2((size_t)os::vm_page_size(), granularity);
const size_t reserved_segments_size = align_up(_number_of_reserved_segments, reserved_segments_alignment);
const size_t committed_segments_size = align_to_page_size(_number_of_committed_segments);
// reserve space for _segmap
if (!_segmap.initialize(reserved_segments_size, committed_segments_size)) {
return false;
}
MemTracker::record_virtual_memory_type((address)_segmap.low_boundary(), mtCode);
assert(_segmap.committed_size() >= (size_t) _number_of_committed_segments, "could not commit enough space for segment map");
assert(_segmap.reserved_size() >= (size_t) _number_of_reserved_segments , "could not reserve enough space for segment map");
assert(_segmap.reserved_size() >= _segmap.committed_size() , "just checking");
// initialize remaining instance variables, heap memory and segmap
clear();
init_segmap_template();
return true;
}
bool CodeHeap::expand_by(size_t size) {
// expand _memory space
size_t dm = align_to_page_size(_memory.committed_size() + size) - _memory.committed_size();
if (dm > 0) {
// Use at least the available uncommitted space if 'size' is larger
if (_memory.uncommitted_size() != 0 && dm > _memory.uncommitted_size()) {
dm = _memory.uncommitted_size();
}
char* base = _memory.low() + _memory.committed_size();
if (!_memory.expand_by(dm)) return false;
on_code_mapping(base, dm);
size_t i = _number_of_committed_segments;
_number_of_committed_segments = size_to_segments(_memory.committed_size());
assert(_number_of_reserved_segments == size_to_segments(_memory.reserved_size()), "number of reserved segments should not change");
assert(_number_of_reserved_segments >= _number_of_committed_segments, "just checking");
// expand _segmap space
size_t ds = align_to_page_size(_number_of_committed_segments) - _segmap.committed_size();
if ((ds > 0) && !_segmap.expand_by(ds)) {
return false;
}
assert(_segmap.committed_size() >= (size_t) _number_of_committed_segments, "just checking");
// initialize additional space (heap memory and segmap)
clear(i, _number_of_committed_segments);
}
return true;
}
void* CodeHeap::allocate(size_t instance_size) {
size_t number_of_segments = size_to_segments(instance_size + header_size());
assert(segments_to_size(number_of_segments) >= sizeof(FreeBlock), "not enough room for FreeList");
// First check if we can satisfy request from freelist
NOT_PRODUCT(verify());
HeapBlock* block = search_freelist(number_of_segments);
NOT_PRODUCT(verify());
if (block != NULL) {
assert(!block->free(), "must not be marked free");
guarantee((char*) block >= _memory.low_boundary() && (char*) block < _memory.high(),
"The newly allocated block " INTPTR_FORMAT " is not within the heap "
"starting with " INTPTR_FORMAT " and ending with " INTPTR_FORMAT,
p2i(block), p2i(_memory.low_boundary()), p2i(_memory.high()));
_max_allocated_capacity = MAX2(_max_allocated_capacity, allocated_capacity());
_blob_count++;
return block->allocated_space();
}
// Ensure minimum size for allocation to the heap.
number_of_segments = MAX2((int)CodeCacheMinBlockLength, (int)number_of_segments);
if (_next_segment + number_of_segments <= _number_of_committed_segments) {
mark_segmap_as_used(_next_segment, _next_segment + number_of_segments, false);
block = block_at(_next_segment);
block->initialize(number_of_segments);
_next_segment += number_of_segments;
guarantee((char*) block >= _memory.low_boundary() && (char*) block < _memory.high(),
"The newly allocated block " INTPTR_FORMAT " is not within the heap "
"starting with " INTPTR_FORMAT " and ending with " INTPTR_FORMAT,
p2i(block), p2i(_memory.low_boundary()), p2i(_memory.high()));
_max_allocated_capacity = MAX2(_max_allocated_capacity, allocated_capacity());
_blob_count++;
return block->allocated_space();
} else {
return NULL;
}
}
// Split the given block into two at the given segment.
// This is helpful when a block was allocated too large
// to trim off the unused space at the end (interpreter).
// It also helps with splitting a large free block during allocation.
// Usage state (used or free) must be set by caller since
// we don't know if the resulting blocks will be used or free.
// split_at is the segment number (relative to segment_for(b))
// where the split happens. The segment with relative
// number split_at is the first segment of the split-off block.
HeapBlock* CodeHeap::split_block(HeapBlock *b, size_t split_at) {
if (b == NULL) return NULL;
// After the split, both blocks must have a size of at least CodeCacheMinBlockLength
assert((split_at >= CodeCacheMinBlockLength) && (split_at + CodeCacheMinBlockLength <= b->length()),
"split position(%d) out of range [0..%d]", (int)split_at, (int)b->length());
size_t split_segment = segment_for(b) + split_at;
size_t b_size = b->length();
size_t newb_size = b_size - split_at;
HeapBlock* newb = block_at(split_segment);
newb->set_length(newb_size);
mark_segmap_as_used(segment_for(newb), segment_for(newb) + newb_size, false);
b->set_length(split_at);
return newb;
}
void CodeHeap::deallocate_tail(void* p, size_t used_size) {
assert(p == find_start(p), "illegal deallocation");
// Find start of HeapBlock
HeapBlock* b = (((HeapBlock *)p) - 1);
assert(b->allocated_space() == p, "sanity check");
size_t actual_number_of_segments = b->length();
size_t used_number_of_segments = size_to_segments(used_size + header_size());
size_t unused_number_of_segments = actual_number_of_segments - used_number_of_segments;
guarantee(used_number_of_segments <= actual_number_of_segments, "Must be!");
HeapBlock* f = split_block(b, used_number_of_segments);
add_to_freelist(f);
NOT_PRODUCT(verify());
}
void CodeHeap::deallocate(void* p) {
assert(p == find_start(p), "illegal deallocation");
// Find start of HeapBlock
HeapBlock* b = (((HeapBlock *)p) - 1);
assert(b->allocated_space() == p, "sanity check");
guarantee((char*) b >= _memory.low_boundary() && (char*) b < _memory.high(),
"The block to be deallocated " INTPTR_FORMAT " is not within the heap "
"starting with " INTPTR_FORMAT " and ending with " INTPTR_FORMAT,
p2i(b), p2i(_memory.low_boundary()), p2i(_memory.high()));
add_to_freelist(b);
NOT_PRODUCT(verify());
}
/**
* The segment map is used to quickly find the the start (header) of a
* code block (e.g. nmethod) when only a pointer to a location inside the
* code block is known. This works as follows:
* - The storage reserved for the code heap is divided into 'segments'.
* - The size of a segment is determined by -XX:CodeCacheSegmentSize=<#bytes>.
* - The size must be a power of two to allow the use of shift operations
* to quickly convert between segment index and segment address.
* - Segment start addresses should be aligned to be multiples of CodeCacheSegmentSize.
* - It seems beneficial for CodeCacheSegmentSize to be equal to os::page_size().
* - Allocation in the code cache can only happen at segment start addresses.
* - Allocation in the code cache is in units of CodeCacheSegmentSize.
* - A pointer in the code cache can be mapped to a segment by calling
* segment_for(addr).
* - The segment map is a byte array where array element [i] is related
* to the i-th segment in the code heap.
* - Each time memory is allocated/deallocated from the code cache,
* the segment map is updated accordingly.
* Note: deallocation does not cause the memory to become "free", as
* indicated by the segment map state "free_sentinel". Deallocation
* just changes the block state from "used" to "free".
* - Elements of the segment map (byte) array are interpreted
* as unsigned integer.
* - Element values normally identify an offset backwards (in segment
* size units) from the associated segment towards the start of
* the block.
* - Some values have a special meaning:
* 0 - This segment is the start of a block (HeapBlock or FreeBlock).
* 255 - The free_sentinel value. This is a free segment, i.e. it is
* not yet allocated and thus does not belong to any block.
* - The value of the current element has to be subtracted from the
* current index to get closer to the start.
* - If the value of the then current element is zero, the block start
* segment is found and iteration stops. Otherwise, start over with the
* previous step.
*
* The following example illustrates a possible state of code cache
* and the segment map: (seg -> segment, nm ->nmethod)
*
* code cache segmap
* ----------- ---------
* seg 1 | nm 1 | -> | 0 |
* seg 2 | nm 1 | -> | 1 |
* ... | nm 1 | -> | .. |
* seg m-1 | nm 1 | -> | m-1 |
* seg m | nm 2 | -> | 0 |
* seg m+1 | nm 2 | -> | 1 |
* ... | nm 2 | -> | 2 |
* ... | nm 2 | -> | .. |
* ... | nm 2 | -> | 0xFE | (free_sentinel-1)
* ... | nm 2 | -> | 1 |
* seg m+n | nm 2 | -> | 2 |
* ... | nm 2 | -> | |
*
* How to read:
* A value of '0' in the segmap indicates that this segment contains the
* beginning of a CodeHeap block. Let's walk through a simple example:
*
* We want to find the start of the block that contains nm 1, and we are
* given a pointer that points into segment m-2. We then read the value
* of segmap[m-2]. The value is an offset that points to the segment
* which contains the start of the block.
*
* Another example: We want to locate the start of nm 2, and we happen to
* get a pointer that points into seg m+n. We first read seg[n+m], which
* returns '2'. So we have to update our segment map index (ix -= segmap[n+m])
* and start over.
*/
// Find block which contains the passed pointer,
// regardless of the block being used or free.
// NULL is returned if anything invalid is detected.
void* CodeHeap::find_block_for(void* p) const {
// Check the pointer to be in committed range.
if (!contains(p)) {
return NULL;
}
address seg_map = (address)_segmap.low();
size_t seg_idx = segment_for(p);
// This may happen in special cases. Just ignore.
// Example: PPC ICache stub generation.
if (is_segment_unused(seg_map[seg_idx])) {
return NULL;
}
// Iterate the segment map chain to find the start of the block.
while (seg_map[seg_idx] > 0) {
// Don't check each segment index to refer to a used segment.
// This method is called extremely often. Therefore, any checking
// has a significant impact on performance. Rely on CodeHeap::verify()
// to do the job on request.
seg_idx -= (int)seg_map[seg_idx];
}
return address_for(seg_idx);
}
// Find block which contains the passed pointer.
// The block must be used, i.e. must not be a FreeBlock.
// Return a pointer that points past the block header.
void* CodeHeap::find_start(void* p) const {
HeapBlock* h = (HeapBlock*)find_block_for(p);
return ((h == NULL) || h->free()) ? NULL : h->allocated_space();
}
// Find block which contains the passed pointer.
// Same as find_start(p), but with additional safety net.
CodeBlob* CodeHeap::find_blob_unsafe(void* start) const {
CodeBlob* result = (CodeBlob*)CodeHeap::find_start(start);
return (result != NULL && result->blob_contains((address)start)) ? result : NULL;
}
size_t CodeHeap::alignment_unit() const {
// this will be a power of two
return _segment_size;
}
size_t CodeHeap::alignment_offset() const {
// The lowest address in any allocated block will be
// equal to alignment_offset (mod alignment_unit).
return sizeof(HeapBlock) & (_segment_size - 1);
}
// Returns the current block if available and used.
// If not, it returns the subsequent block (if available), NULL otherwise.
// Free blocks are merged, therefore there is at most one free block
// between two used ones. As a result, the subsequent block (if available) is
// guaranteed to be used.
// The returned pointer points past the block header.
void* CodeHeap::next_used(HeapBlock* b) const {
if (b != NULL && b->free()) b = next_block(b);
assert(b == NULL || !b->free(), "must be in use or at end of heap");
return (b == NULL) ? NULL : b->allocated_space();
}
// Returns the first used HeapBlock
// The returned pointer points to the block header.
HeapBlock* CodeHeap::first_block() const {
if (_next_segment > 0)
return block_at(0);
return NULL;
}
// The returned pointer points to the block header.
HeapBlock* CodeHeap::block_start(void* q) const {
HeapBlock* b = (HeapBlock*)find_start(q);
if (b == NULL) return NULL;
return b - 1;
}
// Returns the next Heap block.
// The returned pointer points to the block header.
HeapBlock* CodeHeap::next_block(HeapBlock *b) const {
if (b == NULL) return NULL;
size_t i = segment_for(b) + b->length();
if (i < _next_segment)
return block_at(i);
return NULL;
}
// Returns current capacity
size_t CodeHeap::capacity() const {
return _memory.committed_size();
}
size_t CodeHeap::max_capacity() const {
return _memory.reserved_size();
}
int CodeHeap::allocated_segments() const {
return (int)_next_segment;
}
size_t CodeHeap::allocated_capacity() const {
// size of used heap - size on freelist
return segments_to_size(_next_segment - _freelist_segments);
}
// Returns size of the unallocated heap block
size_t CodeHeap::heap_unallocated_capacity() const {
// Total number of segments - number currently used
return segments_to_size(_number_of_reserved_segments - _next_segment);
}
// Free list management
FreeBlock* CodeHeap::following_block(FreeBlock *b) {
return (FreeBlock*)(((address)b) + _segment_size * b->length());
}
// Inserts block b after a
void CodeHeap::insert_after(FreeBlock* a, FreeBlock* b) {
assert(a != NULL && b != NULL, "must be real pointers");
// Link b into the list after a
b->set_link(a->link());
a->set_link(b);
// See if we can merge blocks
merge_right(b); // Try to make b bigger
merge_right(a); // Try to make a include b
}
// Try to merge this block with the following block
bool CodeHeap::merge_right(FreeBlock* a) {
assert(a->free(), "must be a free block");
if (following_block(a) == a->link()) {
assert(a->link() != NULL && a->link()->free(), "must be free too");
// Remember linked (following) block. invalidate should only zap header of this block.
size_t follower = segment_for(a->link());
// Merge block a to include the following block.
a->set_length(a->length() + a->link()->length());
a->set_link(a->link()->link());
// Update the segment map and invalidate block contents.
mark_segmap_as_used(follower, segment_for(a) + a->length(), true);
// Block contents has already been invalidated by add_to_freelist.
// What's left is the header of the following block which now is
// in the middle of the merged block. Just zap one segment.
invalidate(follower, follower + 1, 0);
_freelist_length--;
return true;
}
return false;
}
void CodeHeap::add_to_freelist(HeapBlock* a) {
FreeBlock* b = (FreeBlock*)a;
size_t bseg = segment_for(b);
_freelist_length++;
assert(b != _freelist, "cannot be removed twice");
// Mark as free and update free space count
_freelist_segments += b->length();
b->set_free();
invalidate(bseg, bseg + b->length(), sizeof(FreeBlock));
// First element in list?
if (_freelist == NULL) {
b->set_link(NULL);
_freelist = b;
return;
}
// Since the freelist is ordered (smaller addresses -> larger addresses) and the
// element we want to insert into the freelist has a smaller address than the first
// element, we can simply add 'b' as the first element and we are done.
if (b < _freelist) {
// Insert first in list
b->set_link(_freelist);
_freelist = b;
merge_right(_freelist);
return;
}
// Scan for right place to put into list.
// List is sorted by increasing addresses.
FreeBlock* prev = _freelist;
FreeBlock* cur = _freelist->link();
if ((_freelist_length > freelist_limit) && (_last_insert_point != NULL)) {
_last_insert_point = (FreeBlock*)find_block_for(_last_insert_point);
if ((_last_insert_point != NULL) && _last_insert_point->free() && (_last_insert_point < b)) {
prev = _last_insert_point;
cur = prev->link();
}
}
while(cur != NULL && cur < b) {
assert(prev < cur, "Freelist must be ordered");
prev = cur;
cur = cur->link();
}
assert((prev < b) && (cur == NULL || b < cur), "free-list must be ordered");
insert_after(prev, b);
_last_insert_point = prev;
}
/**
* Search freelist for an entry on the list with the best fit.
* @return NULL, if no one was found
*/
HeapBlock* CodeHeap::search_freelist(size_t length) {
FreeBlock* found_block = NULL;
FreeBlock* found_prev = NULL;
size_t found_length = _next_segment; // max it out to begin with
HeapBlock* res = NULL;
FreeBlock* prev = NULL;
FreeBlock* cur = _freelist;
length = length < CodeCacheMinBlockLength ? CodeCacheMinBlockLength : length;
// Search for best-fitting block
while(cur != NULL) {
size_t cur_length = cur->length();
if (cur_length == length) {
// We have a perfect fit
found_block = cur;
found_prev = prev;
found_length = cur_length;
break;
} else if ((cur_length > length) && (cur_length < found_length)) {
// This is a new, closer fit. Remember block, its previous element, and its length
found_block = cur;
found_prev = prev;
found_length = cur_length;
}
// Next element in list
prev = cur;
cur = cur->link();
}
if (found_block == NULL) {
// None found
return NULL;
}
// Exact (or at least good enough) fit. Remove from list.
// Don't leave anything on the freelist smaller than CodeCacheMinBlockLength.
if (found_length - length < CodeCacheMinBlockLength) {
_freelist_length--;
length = found_length;
if (found_prev == NULL) {
assert(_freelist == found_block, "sanity check");
_freelist = _freelist->link();
} else {
assert((found_prev->link() == found_block), "sanity check");
// Unmap element
found_prev->set_link(found_block->link());
}
res = (HeapBlock*)found_block;
// sizeof(HeapBlock) < sizeof(FreeBlock).
// Invalidate the additional space that FreeBlock occupies.
// The rest of the block should already be invalidated.
// This is necessary due to a dubious assert in nmethod.cpp(PcDescCache::reset_to()).
// Can't use invalidate() here because it works on segment_size units (too coarse).
DEBUG_ONLY(memset((void*)res->allocated_space(), badCodeHeapNewVal, sizeof(FreeBlock) - sizeof(HeapBlock)));
} else {
// Truncate the free block and return the truncated part
// as new HeapBlock. The remaining free block does not
// need to be updated, except for it's length. Truncating
// the segment map does not invalidate the leading part.
res = split_block(found_block, found_length - length);
}
res->set_used();
_freelist_segments -= length;
return res;
}
int CodeHeap::defrag_segmap(bool do_defrag) {
int extra_hops_used = 0;
int extra_hops_free = 0;
int blocks_used = 0;
int blocks_free = 0;
for(HeapBlock* h = first_block(); h != NULL; h = next_block(h)) {
size_t beg = segment_for(h);
size_t end = segment_for(h) + h->length();
int extra_hops = segmap_hops(beg, end);
if (h->free()) {
extra_hops_free += extra_hops;
blocks_free++;
} else {
extra_hops_used += extra_hops;
blocks_used++;
}
if (do_defrag && (extra_hops > 0)) {
mark_segmap_as_used(beg, end, false);
}
}
return extra_hops_used + extra_hops_free;
}
// Count the hops required to get from the last segment of a
// heap block to the block header segment. For the optimal case,
// #hops = ((#segments-1)+(free_sentinel-2))/(free_sentinel-1)
// The range of segments to be checked is given by [beg..end).
// Return the number of extra hops required. There may be extra hops
// due to the is_FreeBlock_join optimization in mark_segmap_as_used().
int CodeHeap::segmap_hops(size_t beg, size_t end) {
if (beg < end) {
// setup _segmap pointers for faster indexing
address p = (address)_segmap.low() + beg;
int hops_expected = (int)(((end-beg-1)+(free_sentinel-2))/(free_sentinel-1));
int nhops = 0;
size_t ix = end-beg-1;
while (p[ix] > 0) {
ix -= p[ix];
nhops++;
}
return (nhops > hops_expected) ? nhops - hops_expected : 0;
}
return 0;
}
//----------------------------------------------------------------------------
// Non-product code
#ifndef PRODUCT
void CodeHeap::print() {
tty->print_cr("The Heap");
}
void CodeHeap::verify() {
if (VerifyCodeCache) {
size_t len = 0;
int count = 0;
for(FreeBlock* b = _freelist; b != NULL; b = b->link()) {
len += b->length();
count++;
// Check if we have merged all free blocks
assert(merge_right(b) == false, "Missed merging opportunity");
}
// Verify that freelist contains the right amount of free space
assert(len == _freelist_segments, "wrong freelist");
for(HeapBlock* h = first_block(); h != NULL; h = next_block(h)) {
if (h->free()) count--;
}
// Verify that the freelist contains the same number of blocks
// than free blocks found on the full list.
assert(count == 0, "missing free blocks");
//---< all free block memory must have been invalidated >---
for(FreeBlock* b = _freelist; b != NULL; b = b->link()) {
for (char* c = (char*)b + sizeof(FreeBlock); c < (char*)b + segments_to_size(b->length()); c++) {
assert(*c == (char)badCodeHeapNewVal, "FreeBlock@" PTR_FORMAT "(" PTR_FORMAT ") not invalidated @byte %d", p2i(b), b->length(), (int)(c - (char*)b));
}
}
address seg_map = (address)_segmap.low();
size_t nseg = 0;
int extra_hops = 0;
count = 0;
for(HeapBlock* b = first_block(); b != NULL; b = next_block(b)) {
size_t seg1 = segment_for(b);
size_t segn = seg1 + b->length();
extra_hops += segmap_hops(seg1, segn);
count++;
for (size_t i = seg1; i < segn; i++) {
nseg++;
//---< Verify segment map marking >---
// All allocated segments, no matter if in a free or used block,
// must be marked "in use".
assert(!is_segment_unused(seg_map[i]), "CodeHeap: unused segment. seg_map[%d]([%d..%d]) = %d, %s block", (int)i, (int)seg1, (int)segn, seg_map[i], b->free()? "free":"used");
assert((unsigned char)seg_map[i] < free_sentinel, "CodeHeap: seg_map[%d]([%d..%d]) = %d (out of range)", (int)i, (int)seg1, (int)segn, seg_map[i]);
}
}
assert(nseg == _next_segment, "CodeHeap: segment count mismatch. found %d, expected %d.", (int)nseg, (int)_next_segment);
assert((count == 0) || (extra_hops < (16 + 2*count)), "CodeHeap: many extra hops due to optimization. blocks: %d, extra hops: %d.", count, extra_hops);
// Verify that the number of free blocks is not out of hand.
static int free_block_threshold = 10000;
if (count > free_block_threshold) {
warning("CodeHeap: # of free blocks > %d", free_block_threshold);
// Double the warning limit
free_block_threshold *= 2;
}
}
}
#endif