koda@google.com
6c4eff32c9
If GC sweeper finds a truncated large object, the page is shrunk to fit. Allows reclaiming memory when a large string is externalized. R=iposva@google.com Review URL: https://codereview.chromium.org//355123002 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@37842 260f80e4-7a28-3924-810f-c04153c831b5
100 lines
3.0 KiB
C++
100 lines
3.0 KiB
C++
// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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#ifndef VM_VIRTUAL_MEMORY_H_
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#define VM_VIRTUAL_MEMORY_H_
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#include "platform/utils.h"
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#include "vm/globals.h"
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#include "vm/memory_region.h"
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namespace dart {
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class VirtualMemory {
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public:
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enum Protection {
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kNoAccess,
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kReadOnly,
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kReadWrite,
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kReadExecute,
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kReadWriteExecute
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};
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// The reserved memory is unmapped on destruction.
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~VirtualMemory();
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uword start() const { return region_.start(); }
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uword end() const { return region_.end(); }
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void* address() const { return region_.pointer(); }
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intptr_t size() const { return region_.size(); }
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static void InitOnce();
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bool Contains(uword addr) const {
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return region_.Contains(addr);
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}
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// Commits the virtual memory area.
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bool Commit(bool is_executable) {
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return Commit(start(), size(), is_executable);
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}
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// Changes the protection of the virtual memory area.
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static bool Protect(void* address, intptr_t size, Protection mode);
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bool Protect(Protection mode) {
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return Protect(address(), size(), mode);
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}
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// Reserves a virtual memory segment with size. If a segment of the requested
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// size cannot be allocated NULL is returned.
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static VirtualMemory* Reserve(intptr_t size);
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// Reserves a virtual memory segment with the start address being aligned to
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// the requested power of two.
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static VirtualMemory* ReserveAligned(intptr_t size, intptr_t alignment);
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static intptr_t PageSize() {
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ASSERT(page_size_ != 0);
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ASSERT(Utils::IsPowerOfTwo(page_size_));
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return page_size_;
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}
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static bool InSamePage(uword address0, uword address1);
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// Truncate this virtual memory segment.
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void Truncate(uword new_start, intptr_t size);
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private:
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// Free a sub segment. On operating systems that support it this
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// can give back the virtual memory to the system.
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void FreeSubSegment(void* address, intptr_t size);
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// This constructor is only used internally when reserving new virtual spaces.
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// It does not reserve any virtual address space on its own.
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VirtualMemory(const MemoryRegion& region, void* reserved_pointer) :
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region_(region.pointer(), region.size()),
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reserved_pointer_(reserved_pointer) { }
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// Commit a reserved memory area, so that the memory can be accessed.
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bool Commit(uword addr, intptr_t size, bool is_executable);
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MemoryRegion region_;
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// The original pointer returned by the OS for this virtual memory
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// allocation or NULL. reserved_pointer_ is non-NULL only for
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// platforms where virtual memory subregions cannot be given back to
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// the OS. When non-null it might not coincide with
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// region_.pointer() if the virtual memory region has been
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// truncated.
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void* reserved_pointer_;
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static uword page_size_;
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DISALLOW_IMPLICIT_CONSTRUCTORS(VirtualMemory);
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};
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} // namespace dart
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#endif // VM_VIRTUAL_MEMORY_H_
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