/* * Copyright (c) 1997, 2022, Oracle and/or its affiliates. All rights reserved. * 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 * or visit www.oracle.com if you need additional information or have any * questions. *
*/
// 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 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", (unsignedint)end, (unsignedint)beg, (unsignedint)(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
}
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");
assert_locked_or_safepoint(CodeCache_lock);
// 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 " PTR_FORMAT " is not within the heap " "starting with " PTR_FORMAT " and ending with " PTR_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 " PTR_FORMAT " is not within the heap " "starting with " PTR_FORMAT " and ending with " PTR_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;
// 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 " PTR_FORMAT " is not within the heap " "starting with " PTR_FORMAT " and ending with " PTR_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 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;
}
// 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(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). returnsizeof(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;
}
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);
}
// 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--; returntrue;
} returnfalse;
}
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;
// 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;
} elseif ((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);
}
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
= checked_cast<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;
}
void CodeHeap::verify() { if (VerifyCodeCache) {
assert_locked_or_safepoint(CodeCache_lock);
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((unsignedchar)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(extra_hops <= _fragmentation_count, "CodeHeap: extra hops wrong. fragmentation: %d, extra hops: %d.", _fragmentation_count, extra_hops); if (extra_hops >= (16 + 2 * count)) {
warning("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. staticint 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
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