/* * Copyright (c) 2001, 2021, 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. *
*/
void PSYoungGen::initialize_virtual_space(ReservedSpace rs,
size_t initial_size,
size_t alignment) {
assert(initial_size != 0, "Should have a finite size");
_virtual_space = new PSVirtualSpace(rs, alignment); if (!virtual_space()->expand_by(initial_size)) {
vm_exit_during_initialization("Could not reserve enough space for object heap");
}
}
if (ZapUnusedHeapArea) { // Mangle newly committed space immediately because it // can be done here more simply that after the new // spaces have been computed.
SpaceMangler::mangle_region(cmr);
}
if (UseNUMA) {
_eden_space = new MutableNUMASpace(virtual_space()->alignment());
} else {
_eden_space = new MutableSpace(virtual_space()->alignment());
}
_from_space = new MutableSpace(virtual_space()->alignment());
_to_space = new MutableSpace(virtual_space()->alignment());
// Compute maximum space sizes for performance counters
size_t alignment = SpaceAlignment;
size_t size = virtual_space()->reserved_size();
size_t max_survivor_size;
size_t max_eden_size;
if (UseAdaptiveSizePolicy) {
max_survivor_size = size / MinSurvivorRatio;
// round the survivor space size down to the nearest alignment // and make sure its size is greater than 0.
max_survivor_size = align_down(max_survivor_size, alignment);
max_survivor_size = MAX2(max_survivor_size, alignment);
// set the maximum size of eden to be the size of the young gen // less two times the minimum survivor size. The minimum survivor // size for UseAdaptiveSizePolicy is one alignment.
max_eden_size = size - 2 * alignment;
} else {
max_survivor_size = size / InitialSurvivorRatio;
// round the survivor space size down to the nearest alignment // and make sure its size is greater than 0.
max_survivor_size = align_down(max_survivor_size, alignment);
max_survivor_size = MAX2(max_survivor_size, alignment);
// set the maximum size of eden to be the size of the young gen // less two times the survivor size when the generation is 100% // committed. The minimum survivor size for -UseAdaptiveSizePolicy // is dependent on the committed portion (current capacity) of the // generation - the less space committed, the smaller the survivor // space, possibly as small as an alignment. However, we are interested // in the case where the young generation is 100% committed, as this // is the point where eden reaches its maximum size. At this point, // the size of a survivor space is max_survivor_size.
max_eden_size = size - 2 * max_survivor_size;
}
_eden_counters = new SpaceCounters("eden", 0, max_eden_size, _eden_space,
_gen_counters);
_from_counters = new SpaceCounters("s0", 1, max_survivor_size, _from_space,
_gen_counters);
_to_counters = new SpaceCounters("s1", 2, max_survivor_size, _to_space,
_gen_counters);
compute_initial_space_boundaries();
}
void PSYoungGen::compute_initial_space_boundaries() { // Compute sizes
size_t size = virtual_space()->committed_size();
assert(size >= 3 * SpaceAlignment, "Young space is not large enough for eden + 2 survivors");
size_t survivor_size = size / InitialSurvivorRatio;
survivor_size = align_down(survivor_size, SpaceAlignment); // ... but never less than an alignment
survivor_size = MAX2(survivor_size, SpaceAlignment);
// Young generation is eden + 2 survivor spaces
size_t eden_size = size - (2 * survivor_size);
// Now go ahead and set 'em.
set_space_boundaries(eden_size, survivor_size);
space_invariants();
if (UsePerfData) {
_eden_counters->update_capacity();
_from_counters->update_capacity();
_to_counters->update_capacity();
}
}
// Initial layout is Eden, to, from. After swapping survivor spaces, // that leaves us with Eden, from, to, which is step one in our two // step resize-with-live-data procedure. char *eden_start = virtual_space()->low(); char *to_start = eden_start + eden_size; char *from_start = to_start + survivor_size; char *from_end = from_start + survivor_size;
#ifndef PRODUCT void PSYoungGen::space_invariants() { // Currently, our eden size cannot shrink to zero
guarantee(eden_space()->capacity_in_bytes() >= SpaceAlignment, "eden too small");
guarantee(from_space()->capacity_in_bytes() >= SpaceAlignment, "from too small");
guarantee(to_space()->capacity_in_bytes() >= SpaceAlignment, "to too small");
// Relationship of spaces to each other char* eden_start = (char*)eden_space()->bottom(); char* eden_end = (char*)eden_space()->end(); char* from_start = (char*)from_space()->bottom(); char* from_end = (char*)from_space()->end(); char* to_start = (char*)to_space()->bottom(); char* to_end = (char*)to_space()->end();
guarantee(eden_start >= virtual_space()->low(), "eden bottom");
guarantee(eden_start < eden_end, "eden space consistency");
guarantee(from_start < from_end, "from space consistency");
guarantee(to_start < to_end, "to space consistency");
// Check whether from space is below to space if (from_start < to_start) { // Eden, from, to
guarantee(eden_end <= from_start, "eden/from boundary");
guarantee(from_end <= to_start, "from/to boundary");
guarantee(to_end <= virtual_space()->high(), "to end");
} else { // Eden, to, from
guarantee(eden_end <= to_start, "eden/to boundary");
guarantee(to_end <= from_start, "to/from boundary");
guarantee(from_end <= virtual_space()->high(), "from end");
}
// More checks that the virtual space is consistent with the spaces
assert(virtual_space()->committed_size() >=
(eden_space()->capacity_in_bytes() +
to_space()->capacity_in_bytes() +
from_space()->capacity_in_bytes()), "Committed size is inconsistent");
assert(virtual_space()->committed_size() <= virtual_space()->reserved_size(), "Space invariant"); char* eden_top = (char*)eden_space()->top(); char* from_top = (char*)from_space()->top(); char* to_top = (char*)to_space()->top();
assert(eden_top <= virtual_space()->high(), "eden top");
assert(from_top <= virtual_space()->high(), "from top");
assert(to_top <= virtual_space()->high(), "to top");
virtual_space()->verify();
} #endif
void PSYoungGen::resize(size_t eden_size, size_t survivor_size) { // Resize the generation if needed. If the generation resize // reports false, do not attempt to resize the spaces. if (resize_generation(eden_size, survivor_size)) { // Then we lay out the spaces inside the generation
resize_spaces(eden_size, survivor_size);
// There used to be this guarantee there. // guarantee ((eden_size + 2*survivor_size) <= max_gen_size(), "incorrect input arguments"); // Code below forces this requirement. In addition the desired eden // size and desired survivor sizes are desired goals and may // exceed the total generation size.
if (desired_size > orig_size) { // Grow the generation
size_t change = desired_size - orig_size;
assert(change % alignment == 0, "just checking");
HeapWord* prev_high = (HeapWord*) virtual_space()->high(); if (!virtual_space()->expand_by(change)) { returnfalse; // Error if we fail to resize!
} if (ZapUnusedHeapArea) { // Mangle newly committed space immediately because it // can be done here more simply that after the new // spaces have been computed.
HeapWord* new_high = (HeapWord*) virtual_space()->high();
MemRegion mangle_region(prev_high, new_high);
SpaceMangler::mangle_region(mangle_region);
}
size_changed = true;
} elseif (desired_size < orig_size) {
size_t desired_change = orig_size - desired_size;
assert(desired_change % alignment == 0, "just checking");
#ifndef PRODUCT // In the numa case eden is not mangled so a survivor space // moving into a region previously occupied by a survivor // may find an unmangled region. Also in the PS case eden // to-space and from-space may not touch (i.e., there may be // gaps between them due to movement while resizing the // spaces). Those gaps must be mangled. void PSYoungGen::mangle_survivors(MutableSpace* s1,
MemRegion s1MR,
MutableSpace* s2,
MemRegion s2MR) { // Check eden and gap between eden and from-space, in deciding // what to mangle in from-space. Check the gap between from-space // and to-space when deciding what to mangle. // // +--------+ +----+ +---+ // | eden | |s1 | |s2 | // +--------+ +----+ +---+ // +-------+ +-----+ // |s1MR | |s2MR | // +-------+ +-----+ // All of survivor-space is properly mangled so find the // upper bound on the mangling for any portion above current s1.
HeapWord* delta_end = MIN2(s1->bottom(), s1MR.end());
MemRegion delta1_left; if (s1MR.start() < delta_end) {
delta1_left = MemRegion(s1MR.start(), delta_end);
s1->mangle_region(delta1_left);
} // Find any portion to the right of the current s1.
HeapWord* delta_start = MAX2(s1->end(), s1MR.start());
MemRegion delta1_right; if (delta_start < s1MR.end()) {
delta1_right = MemRegion(delta_start, s1MR.end());
s1->mangle_region(delta1_right);
}
// Similarly for the second survivor space except that // any of the new region that overlaps with the current // region of the first survivor space has already been // mangled.
delta_end = MIN2(s2->bottom(), s2MR.end());
delta_start = MAX2(s2MR.start(), s1->end());
MemRegion delta2_left; if (s2MR.start() < delta_end) {
delta2_left = MemRegion(s2MR.start(), delta_end);
s2->mangle_region(delta2_left);
}
delta_start = MAX2(s2->end(), s2MR.start());
MemRegion delta2_right; if (delta_start < s2MR.end()) {
s2->mangle_region(delta2_right);
}
// There's nothing to do if the new sizes are the same as the current if (requested_survivor_size == to_space()->capacity_in_bytes() &&
requested_survivor_size == from_space()->capacity_in_bytes() &&
requested_eden_size == eden_space()->capacity_in_bytes()) {
log_trace(gc, ergo)(" capacities are the right sizes, returning"); return;
}
bool eden_from_to_order = from_start < to_start; // Check whether from space is below to space if (eden_from_to_order) { // Eden, from, to
eden_from_to_order = true;
log_trace(gc, ergo)(" Eden, from, to:");
// Set eden // "requested_eden_size" is a goal for the size of eden // and may not be attainable. "eden_size" below is // calculated based on the location of from-space and // the goal for the size of eden. from-space is // fixed in place because it contains live data. // The calculation is done this way to avoid 32bit // overflow (i.e., eden_start + requested_eden_size // may too large for representation in 32bits).
size_t eden_size; if (maintain_minimum) { // Only make eden larger than the requested size if // the minimum size of the generation has to be maintained. // This could be done in general but policy at a higher // level is determining a requested size for eden and that // should be honored unless there is a fundamental reason.
eden_size = pointer_delta(from_start,
eden_start, sizeof(char));
} else {
eden_size = MIN2(requested_eden_size,
pointer_delta(from_start, eden_start, sizeof(char)));
}
// To may resize into from space as long as it is clear of live data. // From space must remain page aligned, though, so we need to do some // extra calculations.
// First calculate an optimal to-space
to_end = (char*)virtual_space()->high();
to_start = (char*)pointer_delta(to_end, (char*)requested_survivor_size, sizeof(char));
// Does the optimal to-space overlap from-space? if (to_start < (char*)from_space()->end()) { // Calculate the minimum offset possible for from_end
size_t from_size = pointer_delta(from_space()->top(), from_start, sizeof(char));
// Should we be in this method if from_space is empty? Why not the set_space method? FIX ME! if (from_size == 0) {
from_size = SpaceAlignment;
} else {
from_size = align_up(from_size, SpaceAlignment);
}
// To space gets priority over eden resizing. Note that we position // to space as if we were able to resize from space, even though from // space is not modified. // Giving eden priority was tried and gave poorer performance.
to_end = (char*)pointer_delta(virtual_space()->high(),
(char*)requested_survivor_size, sizeof(char));
to_end = MIN2(to_end, from_start);
to_start = (char*)pointer_delta(to_end, (char*)requested_survivor_size, sizeof(char)); // if the space sizes are to be increased by several times then // 'to_start' will point beyond the young generation. In this case // 'to_start' should be adjusted.
to_start = MAX2(to_start, eden_start + SpaceAlignment);
// Compute how big eden can be, then adjust end. // See comments above on calculating eden_end.
size_t eden_size; if (maintain_minimum) {
eden_size = pointer_delta(to_start, eden_start, sizeof(char));
} else {
eden_size = MIN2(requested_eden_size,
pointer_delta(to_start, eden_start, sizeof(char)));
}
eden_end = eden_start + eden_size;
assert(eden_end >= eden_start, "addition overflowed");
// Could choose to not let eden shrink // to_start = MAX2(to_start, eden_end);
// Don't let eden shrink down to 0 or less.
eden_end = MAX2(eden_end, eden_start + SpaceAlignment);
to_start = MAX2(to_start, eden_end);
guarantee((HeapWord*)from_start <= from_space()->bottom(), "from start moved to the right");
guarantee((HeapWord*)from_end >= from_space()->top(), "from end moved into live data");
assert(is_object_aligned(eden_start), "checking alignment");
assert(is_object_aligned(from_start), "checking alignment");
assert(is_object_aligned(to_start), "checking alignment");
if (ZapUnusedHeapArea) { // NUMA is a special case because a numa space is not mangled // in order to not prematurely bind its address to memory to // the wrong memory (i.e., don't want the GC thread to first // touch the memory). The survivor spaces are not numa // spaces and are mangled. if (UseNUMA) { if (eden_from_to_order) {
mangle_survivors(from_space(), fromMR, to_space(), toMR);
} else {
mangle_survivors(to_space(), toMR, from_space(), fromMR);
}
}
// If not mangling the spaces, do some checking to verify that // the spaces are already mangled. // The spaces should be correctly mangled at this point so // do some checking here. Note that they are not being mangled // in the calls to initialize(). // Must check mangling before the spaces are reshaped. Otherwise, // the bottom or end of one space may have moved into an area // covered by another space and a failure of the check may // not correctly indicate which space is not properly mangled.
HeapWord* limit = (HeapWord*) virtual_space()->high();
eden_space()->check_mangled_unused_area(limit);
from_space()->check_mangled_unused_area(limit);
to_space()->check_mangled_unused_area(limit);
}
// When an existing space is being initialized, it is not // mangled because the space has been previously mangled.
eden_space()->initialize(edenMR,
SpaceDecorator::Clear,
SpaceDecorator::DontMangle,
MutableSpace::SetupPages,
workers);
to_space()->initialize(toMR,
SpaceDecorator::Clear,
SpaceDecorator::DontMangle,
MutableSpace::SetupPages,
workers);
from_space()->initialize(fromMR,
SpaceDecorator::DontClear,
SpaceDecorator::DontMangle,
MutableSpace::SetupPages,
workers);
assert(from_space()->top() == old_from_top, "from top changed!");
size_t PSYoungGen::capacity_in_bytes() const { return eden_space()->capacity_in_bytes()
+ from_space()->capacity_in_bytes(); // to_space() is only used during scavenge
}
size_t PSYoungGen::used_in_bytes() const { return eden_space()->used_in_bytes()
+ from_space()->used_in_bytes(); // to_space() is only used during scavenge
}
size_t PSYoungGen::free_in_bytes() const { return eden_space()->free_in_bytes()
+ from_space()->free_in_bytes(); // to_space() is only used during scavenge
}
size_t PSYoungGen::capacity_in_words() const { return eden_space()->capacity_in_words()
+ from_space()->capacity_in_words(); // to_space() is only used during scavenge
}
size_t PSYoungGen::used_in_words() const { return eden_space()->used_in_words()
+ from_space()->used_in_words(); // to_space() is only used during scavenge
}
size_t PSYoungGen::free_in_words() const { return eden_space()->free_in_words()
+ from_space()->free_in_words(); // to_space() is only used during scavenge
}
// This method assumes that from-space has live data and that // any shrinkage of the young gen is limited by location of // from-space.
size_t PSYoungGen::available_to_live() {
size_t delta_in_survivor = 0;
MutableSpace* space_shrinking = NULL; if (from_space()->end() > to_space()->end()) {
space_shrinking = from_space();
} else {
space_shrinking = to_space();
}
// Include any space that is committed but not included in // the survivor spaces.
assert(((HeapWord*)virtual_space()->high()) >= space_shrinking->end(), "Survivor space beyond high end");
size_t unused_committed = pointer_delta(virtual_space()->high(),
space_shrinking->end(), sizeof(char));
if (space_shrinking->is_empty()) { // Don't let the space shrink to 0
assert(space_shrinking->capacity_in_bytes() >= SpaceAlignment, "Space is too small");
delta_in_survivor = space_shrinking->capacity_in_bytes() - SpaceAlignment;
} else {
delta_in_survivor = pointer_delta(space_shrinking->end(),
space_shrinking->top(), sizeof(char));
}
// Return the number of bytes available for resizing down the young // generation. This is the minimum of // input "bytes" // bytes to the minimum young gen size // bytes to the size currently being used + some small extra
size_t PSYoungGen::limit_gen_shrink(size_t bytes) { // Allow shrinkage into the current eden but keep eden large enough // to maintain the minimum young gen size
bytes = MIN3(bytes, available_to_min_gen(), available_to_live()); return align_down(bytes, virtual_space()->alignment());
}
HeapWord* new_end = (HeapWord*)virtual_space()->high();
assert(new_end >= space_shrinking->bottom(), "Shrink was too large"); // Was there a shrink of the survivor space? if (new_end < space_shrinking->end()) {
MemRegion mr(space_shrinking->bottom(), new_end);
// This method currently does not expect to expand into eden (i.e., // the virtual space boundaries is expected to be consistent // with the eden boundaries.. void PSYoungGen::post_resize() {
assert_locked_or_safepoint(Heap_lock);
assert((eden_space()->bottom() < to_space()->bottom()) &&
(eden_space()->bottom() < from_space()->bottom()), "Eden is assumed to be below the survivor spaces");
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