truffle: src/share/vm/runtime/virtualspace.cpp comparison

comparison src/share/vm/runtime/virtualspace.cpp @ 0:a61af66fc99e jdk7-b24

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author	duke
date	Sat, 01 Dec 2007 00:00:00 +0000
parents
children	1fdb98a17101 37f87013dfd8

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--1:000000000000
+:a61af66fc99e
+/*
+* Copyright 1997-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+* CA 95054 USA or visit www.sun.com if you need additional information or
+* have any questions.
+*
+*/
+#include "incls/_precompiled.incl"
+#include "incls/_virtualspace.cpp.incl"
+// ReservedSpace
+ReservedSpace::ReservedSpace(size_t size) {
+initialize(size, 0, false, NULL);
+}
+ReservedSpace::ReservedSpace(size_t size, size_t alignment,
+bool large, char* requested_address) {
+initialize(size, alignment, large, requested_address);
+}
+char *
+ReservedSpace::align_reserved_region(char* addr, const size_t len,
+const size_t prefix_size,
+const size_t prefix_align,
+const size_t suffix_size,
+const size_t suffix_align)
+{
+assert(addr != NULL, "sanity");
+const size_t required_size = prefix_size + suffix_size;
+assert(len >= required_size, "len too small");
+const size_t s = size_t(addr);
+const size_t beg_ofs = s + prefix_size & suffix_align - 1;
+const size_t beg_delta = beg_ofs == 0 ? 0 : suffix_align - beg_ofs;
+if (len < beg_delta + required_size) {
+return NULL; // Cannot do proper alignment.
+}
+const size_t end_delta = len - (beg_delta + required_size);
+if (beg_delta != 0) {
+os::release_memory(addr, beg_delta);
+}
+if (end_delta != 0) {
+char* release_addr = (char*) (s + beg_delta + required_size);
+os::release_memory(release_addr, end_delta);
+}
+return (char*) (s + beg_delta);
+}
+char* ReservedSpace::reserve_and_align(const size_t reserve_size,
+const size_t prefix_size,
+const size_t prefix_align,
+const size_t suffix_size,
+const size_t suffix_align)
+{
+assert(reserve_size > prefix_size + suffix_size, "should not be here");
+char* raw_addr = os::reserve_memory(reserve_size, NULL, prefix_align);
+if (raw_addr == NULL) return NULL;
+char* result = align_reserved_region(raw_addr, reserve_size, prefix_size,
+prefix_align, suffix_size,
+suffix_align);
+if (result == NULL && !os::release_memory(raw_addr, reserve_size)) {
+fatal("os::release_memory failed");
+}
+#ifdef ASSERT
+if (result != NULL) {
+const size_t raw = size_t(raw_addr);
+const size_t res = size_t(result);
+assert(res >= raw, "alignment decreased start addr");
+assert(res + prefix_size + suffix_size <= raw + reserve_size,
+"alignment increased end addr");
+assert((res & prefix_align - 1) == 0, "bad alignment of prefix");
+assert((res + prefix_size & suffix_align - 1) == 0,
+"bad alignment of suffix");
+}
+#endif
+return result;
+}
+ReservedSpace::ReservedSpace(const size_t prefix_size,
+const size_t prefix_align,
+const size_t suffix_size,
+const size_t suffix_align)
+{
+assert(prefix_size != 0, "sanity");
+assert(prefix_align != 0, "sanity");
+assert(suffix_size != 0, "sanity");
+assert(suffix_align != 0, "sanity");
+assert((prefix_size & prefix_align - 1) == 0,
+"prefix_size not divisible by prefix_align");
+assert((suffix_size & suffix_align - 1) == 0,
+"suffix_size not divisible by suffix_align");
+assert((suffix_align & prefix_align - 1) == 0,
+"suffix_align not divisible by prefix_align");
+// On systems where the entire region has to be reserved and committed up
+// front, the compound alignment normally done by this method is unnecessary.
+const bool try_reserve_special = UseLargePages &&
+prefix_align == os::large_page_size();
+if (!os::can_commit_large_page_memory() && try_reserve_special) {
+initialize(prefix_size + suffix_size, prefix_align, true);
+return;
+}
+_base = NULL;
+_size = 0;
+_alignment = 0;
+_special = false;
+// Optimistically try to reserve the exact size needed.
+const size_t size = prefix_size + suffix_size;
+char* addr = os::reserve_memory(size, NULL, prefix_align);
+if (addr == NULL) return;
+// Check whether the result has the needed alignment (unlikely unless
+// prefix_align == suffix_align).
+const size_t ofs = size_t(addr) + prefix_size & suffix_align - 1;
+if (ofs != 0) {
+// Wrong alignment.  Release, allocate more space and do manual alignment.
+//
+// On most operating systems, another allocation with a somewhat larger size
+// will return an address "close to" that of the previous allocation.  The
+// result is often the same address (if the kernel hands out virtual
+// addresses from low to high), or an address that is offset by the increase
+// in size.  Exploit that to minimize the amount of extra space requested.
+if (!os::release_memory(addr, size)) {
+fatal("os::release_memory failed");
+}
+const size_t extra = MAX2(ofs, suffix_align - ofs);
+addr = reserve_and_align(size + extra, prefix_size, prefix_align,
+suffix_size, suffix_align);
+if (addr == NULL) {
+// Try an even larger region.  If this fails, address space is exhausted.
+addr = reserve_and_align(size + suffix_align, prefix_size,
+prefix_align, suffix_size, suffix_align);
+}
+}
+_base = addr;
+_size = size;
+_alignment = prefix_align;
+}
+void ReservedSpace::initialize(size_t size, size_t alignment, bool large,
+char* requested_address) {
+const size_t granularity = os::vm_allocation_granularity();
+assert((size & granularity - 1) == 0,
+"size not aligned to os::vm_allocation_granularity()");
+assert((alignment & granularity - 1) == 0,
+"alignment not aligned to os::vm_allocation_granularity()");
+assert(alignment == 0 || is_power_of_2((intptr_t)alignment),
+"not a power of 2");
+_base = NULL;
+_size = 0;
+_special = false;
+_alignment = 0;
+if (size == 0) {
+return;
+}
+// If OS doesn't support demand paging for large page memory, we need
+// to use reserve_memory_special() to reserve and pin the entire region.
+bool special = large && !os::can_commit_large_page_memory();
+char* base = NULL;
+if (special) {
+// It's not hard to implement reserve_memory_special() such that it can
+// allocate at fixed address, but there seems no use of this feature
+// for now, so it's not implemented.
+assert(requested_address == NULL, "not implemented");
+base = os::reserve_memory_special(size);
+if (base != NULL) {
+// Check alignment constraints
+if (alignment > 0) {
+assert((uintptr_t) base % alignment == 0,
+"Large pages returned a non-aligned address");
+}
+_special = true;
+} else {
+// failed; try to reserve regular memory below
+}
+}
+if (base == NULL) {
+// Optimistically assume that the OSes returns an aligned base pointer.
+// When reserving a large address range, most OSes seem to align to at
+// least 64K.
+// If the memory was requested at a particular address, use
+// os::attempt_reserve_memory_at() to avoid over mapping something
+// important.  If available space is not detected, return NULL.
+if (requested_address != 0) {
+base = os::attempt_reserve_memory_at(size, requested_address);
+} else {
+base = os::reserve_memory(size, NULL, alignment);
+}
+if (base == NULL) return;
+// Check alignment constraints
+if (alignment > 0 && ((size_t)base & alignment - 1) != 0) {
+// Base not aligned, retry
+if (!os::release_memory(base, size)) fatal("os::release_memory failed");
+// Reserve size large enough to do manual alignment and
+// increase size to a multiple of the desired alignment
+size = align_size_up(size, alignment);
+size_t extra_size = size + alignment;
+char* extra_base = os::reserve_memory(extra_size, NULL, alignment);
+if (extra_base == NULL) return;
+// Do manual alignement
+base = (char*) align_size_up((uintptr_t) extra_base, alignment);
+assert(base >= extra_base, "just checking");
+// Release unused areas
+size_t unused_bottom_size = base - extra_base;
+size_t unused_top_size = extra_size - size - unused_bottom_size;
+assert(unused_bottom_size % os::vm_allocation_granularity() == 0,
+"size not allocation aligned");
+assert(unused_top_size % os::vm_allocation_granularity() == 0,
+"size not allocation aligned");
+if (unused_bottom_size > 0) {
+os::release_memory(extra_base, unused_bottom_size);
+}
+if (unused_top_size > 0) {
+os::release_memory(base + size, unused_top_size);
+}
+}
+}
+// Done
+_base = base;
+_size = size;
+_alignment = MAX2(alignment, (size_t) os::vm_page_size());
+assert(markOopDesc::encode_pointer_as_mark(_base)->decode_pointer() == _base,
+"area must be distinguisable from marks for mark-sweep");
+assert(markOopDesc::encode_pointer_as_mark(&_base[size])->decode_pointer() == &_base[size],
+"area must be distinguisable from marks for mark-sweep");
+}
+ReservedSpace::ReservedSpace(char* base, size_t size, size_t alignment,
+bool special) {
+assert((size % os::vm_allocation_granularity()) == 0,
+"size not allocation aligned");
+_base = base;
+_size = size;
+_alignment = alignment;
+_special = special;
+}
+ReservedSpace ReservedSpace::first_part(size_t partition_size, size_t alignment,
+bool split, bool realloc) {
+assert(partition_size <= size(), "partition failed");
+if (split) {
+os::split_reserved_memory(_base, _size, partition_size, realloc);
+}
+ReservedSpace result(base(), partition_size, alignment, special());
+return result;
+}
+ReservedSpace
+ReservedSpace::last_part(size_t partition_size, size_t alignment) {
+assert(partition_size <= size(), "partition failed");
+ReservedSpace result(base() + partition_size, size() - partition_size,
+alignment, special());
+return result;
+}
+size_t ReservedSpace::page_align_size_up(size_t size) {
+return align_size_up(size, os::vm_page_size());
+}
+size_t ReservedSpace::page_align_size_down(size_t size) {
+return align_size_down(size, os::vm_page_size());
+}
+size_t ReservedSpace::allocation_align_size_up(size_t size) {
+return align_size_up(size, os::vm_allocation_granularity());
+}
+size_t ReservedSpace::allocation_align_size_down(size_t size) {
+return align_size_down(size, os::vm_allocation_granularity());
+}
+void ReservedSpace::release() {
+if (is_reserved()) {
+if (special()) {
+os::release_memory_special(_base, _size);
+} else{
+os::release_memory(_base, _size);
+}
+_base = NULL;
+_size = 0;
+_special = false;
+}
+}
+// VirtualSpace
+VirtualSpace::VirtualSpace() {
+_low_boundary           = NULL;
+_high_boundary          = NULL;
+_low                    = NULL;
+_high                   = NULL;
+_lower_high             = NULL;
+_middle_high            = NULL;
+_upper_high             = NULL;
+_lower_high_boundary    = NULL;
+_middle_high_boundary   = NULL;
+_upper_high_boundary    = NULL;
+_lower_alignment        = 0;
+_middle_alignment       = 0;
+_upper_alignment        = 0;
+}
+bool VirtualSpace::initialize(ReservedSpace rs, size_t committed_size) {
+if(!rs.is_reserved()) return false;  // allocation failed.
+assert(_low_boundary == NULL, "VirtualSpace already initialized");
+_low_boundary  = rs.base();
+_high_boundary = low_boundary() + rs.size();
+_low = low_boundary();
+_high = low();
+_special = rs.special();
+// When a VirtualSpace begins life at a large size, make all future expansion
+// and shrinking occur aligned to a granularity of large pages.  This avoids
+// fragmentation of physical addresses that inhibits the use of large pages
+// by the OS virtual memory system.  Empirically,  we see that with a 4MB
+// page size, the only spaces that get handled this way are codecache and
+// the heap itself, both of which provide a substantial performance
+// boost in many benchmarks when covered by large pages.
+//
+// No attempt is made to force large page alignment at the very top and
+// bottom of the space if they are not aligned so already.
+_lower_alignment  = os::vm_page_size();
+_middle_alignment = os::page_size_for_region(rs.size(), rs.size(), 1);
+_upper_alignment  = os::vm_page_size();
+// End of each region
+_lower_high_boundary = (char*) round_to((intptr_t) low_boundary(), middle_alignment());
+_middle_high_boundary = (char*) round_down((intptr_t) high_boundary(), middle_alignment());
+_upper_high_boundary = high_boundary();
+// High address of each region
+_lower_high = low_boundary();
+_middle_high = lower_high_boundary();
+_upper_high = middle_high_boundary();
+// commit to initial size
+if (committed_size > 0) {
+if (!expand_by(committed_size)) {
+return false;
+}
+}
+return true;
+}
+VirtualSpace::~VirtualSpace() {
+release();
+}
+void VirtualSpace::release() {
+(void)os::release_memory(low_boundary(), reserved_size());
+_low_boundary           = NULL;
+_high_boundary          = NULL;
+_low                    = NULL;
+_high                   = NULL;
+_lower_high             = NULL;
+_middle_high            = NULL;
+_upper_high             = NULL;
+_lower_high_boundary    = NULL;
+_middle_high_boundary   = NULL;
+_upper_high_boundary    = NULL;
+_lower_alignment        = 0;
+_middle_alignment       = 0;
+_upper_alignment        = 0;
+_special                = false;
+}
+size_t VirtualSpace::committed_size() const {
+return pointer_delta(high(), low(), sizeof(char));
+}
+size_t VirtualSpace::reserved_size() const {
+return pointer_delta(high_boundary(), low_boundary(), sizeof(char));
+}
+size_t VirtualSpace::uncommitted_size()  const {
+return reserved_size() - committed_size();
+}
+bool VirtualSpace::contains(const void* p) const {
+return low() <= (const char*) p && (const char*) p < high();
+}
+/*
+First we need to determine if a particular virtual space is using large
+pages.  This is done at the initialize function and only virtual spaces
+that are larger than LargePageSizeInBytes use large pages.  Once we
+have determined this, all expand_by and shrink_by calls must grow and
+shrink by large page size chunks.  If a particular request
+is within the current large page, the call to commit and uncommit memory
+can be ignored.  In the case that the low and high boundaries of this
+space is not large page aligned, the pages leading to the first large
+page address and the pages after the last large page address must be
+allocated with default pages.
+*/
+bool VirtualSpace::expand_by(size_t bytes, bool pre_touch) {
+if (uncommitted_size() < bytes) return false;
+if (special()) {
+// don't commit memory if the entire space is pinned in memory
+_high += bytes;
+return true;
+}
+char* previous_high = high();
+char* unaligned_new_high = high() + bytes;
+assert(unaligned_new_high <= high_boundary(),
+"cannot expand by more than upper boundary");
+// Calculate where the new high for each of the regions should be.  If
+// the low_boundary() and high_boundary() are LargePageSizeInBytes aligned
+// then the unaligned lower and upper new highs would be the
+// lower_high() and upper_high() respectively.
+char* unaligned_lower_new_high =
+MIN2(unaligned_new_high, lower_high_boundary());
+char* unaligned_middle_new_high =
+MIN2(unaligned_new_high, middle_high_boundary());
+char* unaligned_upper_new_high =
+MIN2(unaligned_new_high, upper_high_boundary());
+// Align the new highs based on the regions alignment.  lower and upper
+// alignment will always be default page size.  middle alignment will be
+// LargePageSizeInBytes if the actual size of the virtual space is in
+// fact larger than LargePageSizeInBytes.
+char* aligned_lower_new_high =
+(char*) round_to((intptr_t) unaligned_lower_new_high, lower_alignment());
+char* aligned_middle_new_high =
+(char*) round_to((intptr_t) unaligned_middle_new_high, middle_alignment());
+char* aligned_upper_new_high =
+(char*) round_to((intptr_t) unaligned_upper_new_high, upper_alignment());
+// Determine which regions need to grow in this expand_by call.
+// If you are growing in the lower region, high() must be in that
+// region so calcuate the size based on high().  For the middle and
+// upper regions, determine the starting point of growth based on the
+// location of high().  By getting the MAX of the region's low address
+// (or the prevoius region's high address) and high(), we can tell if it
+// is an intra or inter region growth.
+size_t lower_needs = 0;
+if (aligned_lower_new_high > lower_high()) {
+lower_needs =
+pointer_delta(aligned_lower_new_high, lower_high(), sizeof(char));
+}
+size_t middle_needs = 0;
+if (aligned_middle_new_high > middle_high()) {
+middle_needs =
+pointer_delta(aligned_middle_new_high, middle_high(), sizeof(char));
+}
+size_t upper_needs = 0;
+if (aligned_upper_new_high > upper_high()) {
+upper_needs =
+pointer_delta(aligned_upper_new_high, upper_high(), sizeof(char));
+}
+// Check contiguity.
+assert(low_boundary() <= lower_high() &&
+lower_high() <= lower_high_boundary(),
+"high address must be contained within the region");
+assert(lower_high_boundary() <= middle_high() &&
+middle_high() <= middle_high_boundary(),
+"high address must be contained within the region");
+assert(middle_high_boundary() <= upper_high() &&
+upper_high() <= upper_high_boundary(),
+"high address must be contained within the region");
+// Commit regions
+if (lower_needs > 0) {
+assert(low_boundary() <= lower_high() &&
+lower_high() + lower_needs <= lower_high_boundary(),
+"must not expand beyond region");
+if (!os::commit_memory(lower_high(), lower_needs)) {
+debug_only(warning("os::commit_memory failed"));
+return false;
+} else {
+_lower_high += lower_needs;
+}
+}
+if (middle_needs > 0) {
+assert(lower_high_boundary() <= middle_high() &&
+middle_high() + middle_needs <= middle_high_boundary(),
+"must not expand beyond region");
+if (!os::commit_memory(middle_high(), middle_needs, middle_alignment())) {
+debug_only(warning("os::commit_memory failed"));
+return false;
+}
+_middle_high += middle_needs;
+}
+if (upper_needs > 0) {
+assert(middle_high_boundary() <= upper_high() &&
+upper_high() + upper_needs <= upper_high_boundary(),
+"must not expand beyond region");
+if (!os::commit_memory(upper_high(), upper_needs)) {
+debug_only(warning("os::commit_memory failed"));
+return false;
+} else {
+_upper_high += upper_needs;
+}
+}
+if (pre_touch || AlwaysPreTouch) {
+int vm_ps = os::vm_page_size();
+for (char* curr = previous_high;
+curr < unaligned_new_high;
+curr += vm_ps) {
+// Note the use of a write here; originally we tried just a read, but
+// since the value read was unused, the optimizer removed the read.
+// If we ever have a concurrent touchahead thread, we'll want to use
+// a read, to avoid the potential of overwriting data (if a mutator
+// thread beats the touchahead thread to a page).  There are various
+// ways of making sure this read is not optimized away: for example,
+// generating the code for a read procedure at runtime.
+*curr = 0;
+}
+}
+_high += bytes;
+return true;
+}
+// A page is uncommitted if the contents of the entire page is deemed unusable.
+// Continue to decrement the high() pointer until it reaches a page boundary
+// in which case that particular page can now be uncommitted.
+void VirtualSpace::shrink_by(size_t size) {
+if (committed_size() < size)
+fatal("Cannot shrink virtual space to negative size");
+if (special()) {
+// don't uncommit if the entire space is pinned in memory
+_high -= size;
+return;
+}
+char* unaligned_new_high = high() - size;
+assert(unaligned_new_high >= low_boundary(), "cannot shrink past lower boundary");
+// Calculate new unaligned address
+char* unaligned_upper_new_high =
+MAX2(unaligned_new_high, middle_high_boundary());
+char* unaligned_middle_new_high =
+MAX2(unaligned_new_high, lower_high_boundary());
+char* unaligned_lower_new_high =
+MAX2(unaligned_new_high, low_boundary());
+// Align address to region's alignment
+char* aligned_upper_new_high =
+(char*) round_to((intptr_t) unaligned_upper_new_high, upper_alignment());
+char* aligned_middle_new_high =
+(char*) round_to((intptr_t) unaligned_middle_new_high, middle_alignment());
+char* aligned_lower_new_high =
+(char*) round_to((intptr_t) unaligned_lower_new_high, lower_alignment());
+// Determine which regions need to shrink
+size_t upper_needs = 0;
+if (aligned_upper_new_high < upper_high()) {
+upper_needs =
+pointer_delta(upper_high(), aligned_upper_new_high, sizeof(char));
+}
+size_t middle_needs = 0;
+if (aligned_middle_new_high < middle_high()) {
+middle_needs =
+pointer_delta(middle_high(), aligned_middle_new_high, sizeof(char));
+}
+size_t lower_needs = 0;
+if (aligned_lower_new_high < lower_high()) {
+lower_needs =
+pointer_delta(lower_high(), aligned_lower_new_high, sizeof(char));
+}
+// Check contiguity.
+assert(middle_high_boundary() <= upper_high() &&
+upper_high() <= upper_high_boundary(),
+"high address must be contained within the region");
+assert(lower_high_boundary() <= middle_high() &&
+middle_high() <= middle_high_boundary(),
+"high address must be contained within the region");
+assert(low_boundary() <= lower_high() &&
+lower_high() <= lower_high_boundary(),
+"high address must be contained within the region");
+// Uncommit
+if (upper_needs > 0) {
+assert(middle_high_boundary() <= aligned_upper_new_high &&
+aligned_upper_new_high + upper_needs <= upper_high_boundary(),
+"must not shrink beyond region");
+if (!os::uncommit_memory(aligned_upper_new_high, upper_needs)) {
+debug_only(warning("os::uncommit_memory failed"));
+return;
+} else {
+_upper_high -= upper_needs;
+}
+}
+if (middle_needs > 0) {
+assert(lower_high_boundary() <= aligned_middle_new_high &&
+aligned_middle_new_high + middle_needs <= middle_high_boundary(),
+"must not shrink beyond region");
+if (!os::uncommit_memory(aligned_middle_new_high, middle_needs)) {
+debug_only(warning("os::uncommit_memory failed"));
+return;
+} else {
+_middle_high -= middle_needs;
+}
+}
+if (lower_needs > 0) {
+assert(low_boundary() <= aligned_lower_new_high &&
+aligned_lower_new_high + lower_needs <= lower_high_boundary(),
+"must not shrink beyond region");
+if (!os::uncommit_memory(aligned_lower_new_high, lower_needs)) {
+debug_only(warning("os::uncommit_memory failed"));
+return;
+} else {
+_lower_high -= lower_needs;
+}
+}
+_high -= size;
+}
+#ifndef PRODUCT
+void VirtualSpace::check_for_contiguity() {
+// Check contiguity.
+assert(low_boundary() <= lower_high() &&
+lower_high() <= lower_high_boundary(),
+"high address must be contained within the region");
+assert(lower_high_boundary() <= middle_high() &&
+middle_high() <= middle_high_boundary(),
+"high address must be contained within the region");
+assert(middle_high_boundary() <= upper_high() &&
+upper_high() <= upper_high_boundary(),
+"high address must be contained within the region");
+assert(low() >= low_boundary(), "low");
+assert(low_boundary() <= lower_high_boundary(), "lower high boundary");
+assert(upper_high_boundary() <= high_boundary(), "upper high boundary");
+assert(high() <= upper_high(), "upper high");
+}
+void VirtualSpace::print() {
+tty->print   ("Virtual space:");
+if (special()) tty->print(" (pinned in memory)");
+tty->cr();
+tty->print_cr(" - committed: %ld", committed_size());
+tty->print_cr(" - reserved:  %ld", reserved_size());
+tty->print_cr(" - [low, high]:     [" INTPTR_FORMAT ", " INTPTR_FORMAT "]",  low(), high());
+tty->print_cr(" - [low_b, high_b]: [" INTPTR_FORMAT ", " INTPTR_FORMAT "]",  low_boundary(), high_boundary());
+}
+#endif

Mercurial > hg > truffle

comparison src/share/vm/runtime/virtualspace.cpp @ 0:a61af66fc99e jdk7-b24