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b2a52f6208
By designating a committed page pool we can guarantee to have physical pages available for lazy allocation in mappings. However, when forking we will overcommit. The assumption is that worst-case it's better for the fork to die due to insufficient physical memory on COW access than the parent that created the region. If a fork wants to ensure that all memory is available (trigger a commit) then it can use madvise. This also means that fork now can gracefully fail if we don't have enough physical pages available.
82 lines
2.7 KiB
C++
82 lines
2.7 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/NonnullRefPtr.h>
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#include <Kernel/Arch/i386/CPU.h>
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#include <Kernel/Assertions.h>
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#include <Kernel/Heap/SlabAllocator.h>
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#include <Kernel/PhysicalAddress.h>
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namespace Kernel {
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class PhysicalPage {
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friend class MemoryManager;
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friend class PageDirectory;
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friend class VMObject;
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MAKE_SLAB_ALLOCATED(PhysicalPage);
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AK_MAKE_NONMOVABLE(PhysicalPage);
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public:
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PhysicalAddress paddr() const { return m_paddr; }
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void ref()
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{
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m_ref_count.fetch_add(1, AK::memory_order_acq_rel);
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}
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void unref()
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{
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if (m_ref_count.fetch_sub(1, AK::memory_order_acq_rel) == 1) {
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if (m_may_return_to_freelist)
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return_to_freelist();
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delete this;
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}
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}
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static NonnullRefPtr<PhysicalPage> create(PhysicalAddress, bool supervisor, bool may_return_to_freelist = true);
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u32 ref_count() const { return m_ref_count.load(AK::memory_order_consume); }
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bool is_shared_zero_page() const;
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bool is_lazy_committed_page() const;
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private:
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PhysicalPage(PhysicalAddress paddr, bool supervisor, bool may_return_to_freelist = true);
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~PhysicalPage() { }
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void return_to_freelist() const;
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Atomic<u32> m_ref_count { 1 };
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bool m_may_return_to_freelist { true };
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bool m_supervisor { false };
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PhysicalAddress m_paddr;
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};
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}
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