Mercurial > hg > truffle
view src/os_cpu/linux_x86/vm/threadLS_linux_x86.cpp @ 453:c96030fff130
6684579: SoftReference processing can be made more efficient
Summary: For current soft-ref clearing policies, we can decide at marking time if a soft-reference will definitely not be cleared, postponing the decision of whether it will definitely be cleared to the final reference processing phase. This can be especially beneficial in the case of concurrent collectors where the marking is usually concurrent but reference processing is usually not.
Reviewed-by: jmasa
author | ysr |
---|---|
date | Thu, 20 Nov 2008 16:56:09 -0800 |
parents | a61af66fc99e |
children | c18cbe5936b8 |
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/* * Copyright 1999-2003 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/_threadLS_linux_x86.cpp.incl" // Map stack pointer (%esp) to thread pointer for faster TLS access // // Here we use a flat table for better performance. Getting current thread // is down to one memory access (read _sp_map[%esp>>12]) in generated code // and two in runtime code (-fPIC code needs an extra load for _sp_map). // // This code assumes stack page is not shared by different threads. It works // in 32-bit VM when page size is 4K (or a multiple of 4K, if that matters). // // Notice that _sp_map is allocated in the bss segment, which is ZFOD // (zero-fill-on-demand). While it reserves 4M address space upfront, // actual memory pages are committed on demand. // // If an application creates and destroys a lot of threads, usually the // stack space freed by a thread will soon get reused by new thread // (this is especially true in NPTL or LinuxThreads in fixed-stack mode). // No memory page in _sp_map is wasted. // // However, it's still possible that we might end up populating & // committing a large fraction of the 4M table over time, but the actual // amount of live data in the table could be quite small. The max wastage // is less than 4M bytes. If it becomes an issue, we could use madvise() // with MADV_DONTNEED to reclaim unused (i.e. all-zero) pages in _sp_map. // MADV_DONTNEED on Linux keeps the virtual memory mapping, but zaps the // physical memory page (i.e. similar to MADV_FREE on Solaris). #ifndef AMD64 Thread* ThreadLocalStorage::_sp_map[1UL << (SP_BITLENGTH - PAGE_SHIFT)]; #endif // !AMD64 void ThreadLocalStorage::generate_code_for_get_thread() { // nothing we can do here for user-level thread } void ThreadLocalStorage::pd_init() { #ifndef AMD64 assert(align_size_down(os::vm_page_size(), PAGE_SIZE) == os::vm_page_size(), "page size must be multiple of PAGE_SIZE"); #endif // !AMD64 } void ThreadLocalStorage::pd_set_thread(Thread* thread) { os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread); #ifndef AMD64 address stack_top = os::current_stack_base(); size_t stack_size = os::current_stack_size(); for (address p = stack_top - stack_size; p < stack_top; p += PAGE_SIZE) { // pd_set_thread() is called with non-NULL value when a new thread is // created/attached, or with NULL value when a thread is about to exit. // If both "thread" and the corresponding _sp_map[] entry are non-NULL, // they should have the same value. Otherwise it might indicate that the // stack page is shared by multiple threads. However, a more likely cause // for this assertion to fail is that an attached thread exited without // detaching itself from VM, which is a program error and could cause VM // to crash. assert(thread == NULL || _sp_map[(uintptr_t)p >> PAGE_SHIFT] == NULL || thread == _sp_map[(uintptr_t)p >> PAGE_SHIFT], "thread exited without detaching from VM??"); _sp_map[(uintptr_t)p >> PAGE_SHIFT] = thread; } #endif // !AMD64 }