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5f2f31861c
This makes misses in the BlockBasedFS's LRU block cache faster by storing the cache entries in one of two doubly-linked list. Dirty and clean cache entries are kept in two separate lists, and move between them when their state changes. This can probably be improved upon further.
333 lines
11 KiB
C++
333 lines
11 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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#include <AK/IntrusiveList.h>
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#include <Kernel/FileSystem/BlockBasedFileSystem.h>
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#include <Kernel/Process.h>
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//#define BBFS_DEBUG
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namespace Kernel {
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struct CacheEntry {
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IntrusiveListNode list_node;
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u32 block_index { 0 };
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u8* data { nullptr };
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bool has_data { false };
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};
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class DiskCache {
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public:
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explicit DiskCache(BlockBasedFS& fs)
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: m_fs(fs)
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, m_cached_block_data(KBuffer::create_with_size(m_entry_count * m_fs.block_size()))
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, m_entries(KBuffer::create_with_size(m_entry_count * sizeof(CacheEntry)))
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{
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for (size_t i = 0; i < m_entry_count; ++i) {
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entries()[i].data = m_cached_block_data.data() + i * m_fs.block_size();
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m_clean_list.append(entries()[i]);
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}
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}
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~DiskCache() { }
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bool is_dirty() const { return m_dirty; }
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void set_dirty(bool b) { m_dirty = b; }
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void mark_all_clean()
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{
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while (auto* entry = m_dirty_list.first())
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m_clean_list.prepend(*entry);
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m_dirty = false;
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}
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void mark_dirty(CacheEntry& entry)
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{
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m_dirty_list.prepend(entry);
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m_dirty = true;
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}
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void mark_clean(CacheEntry& entry)
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{
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m_clean_list.prepend(entry);
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}
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CacheEntry& get(u32 block_index) const
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{
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if (auto it = m_hash.find(block_index); it != m_hash.end()) {
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auto& entry = const_cast<CacheEntry&>(*it->value);
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ASSERT(entry.block_index == block_index);
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return entry;
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}
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if (m_clean_list.is_empty()) {
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// Not a single clean entry! Flush writes and try again.
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// NOTE: We want to make sure we only call FileBackedFS flush here,
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// not some FileBackedFS subclass flush!
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m_fs.flush_writes_impl();
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return get(block_index);
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}
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ASSERT(m_clean_list.last());
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auto& new_entry = *m_clean_list.last();
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m_clean_list.prepend(new_entry);
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m_hash.remove(new_entry.block_index);
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m_hash.set(block_index, &new_entry);
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new_entry.block_index = block_index;
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new_entry.has_data = false;
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return new_entry;
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}
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const CacheEntry* entries() const { return (const CacheEntry*)m_entries.data(); }
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CacheEntry* entries() { return (CacheEntry*)m_entries.data(); }
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template<typename Callback>
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void for_each_clean_entry(Callback callback)
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{
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for (auto& entry : m_clean_list)
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callback(entry);
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}
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template<typename Callback>
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void for_each_dirty_entry(Callback callback)
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{
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for (auto& entry : m_dirty_list)
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callback(entry);
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}
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private:
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BlockBasedFS& m_fs;
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size_t m_entry_count { 10000 };
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mutable HashMap<u32, CacheEntry*> m_hash;
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mutable IntrusiveList<CacheEntry, &CacheEntry::list_node> m_clean_list;
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mutable IntrusiveList<CacheEntry, &CacheEntry::list_node> m_dirty_list;
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KBuffer m_cached_block_data;
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KBuffer m_entries;
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bool m_dirty { false };
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};
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BlockBasedFS::BlockBasedFS(FileDescription& file_description)
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: FileBackedFS(file_description)
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{
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ASSERT(file_description.file().is_seekable());
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}
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BlockBasedFS::~BlockBasedFS()
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{
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}
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int BlockBasedFS::write_block(unsigned index, const UserOrKernelBuffer& data, size_t count, size_t offset, bool allow_cache)
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{
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ASSERT(m_logical_block_size);
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ASSERT(offset + count <= block_size());
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#ifdef BBFS_DEBUG
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klog() << "BlockBasedFileSystem::write_block " << index << ", size=" << count;
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#endif
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if (!allow_cache) {
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flush_specific_block_if_needed(index);
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u32 base_offset = static_cast<u32>(index) * static_cast<u32>(block_size()) + offset;
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file_description().seek(base_offset, SEEK_SET);
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auto nwritten = file_description().write(data, count);
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if (nwritten.is_error())
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return -EIO; // TODO: Return error code as-is, could be -EFAULT!
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ASSERT(nwritten.value() == count);
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return 0;
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}
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auto& entry = cache().get(index);
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if (count < block_size()) {
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// Fill the cache first.
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read_block(index, nullptr, block_size());
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}
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if (!data.read(entry.data + offset, count))
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return -EFAULT;
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cache().mark_dirty(entry);
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entry.has_data = true;
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return 0;
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}
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bool BlockBasedFS::raw_read(unsigned index, UserOrKernelBuffer& buffer)
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{
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u32 base_offset = static_cast<u32>(index) * static_cast<u32>(m_logical_block_size);
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file_description().seek(base_offset, SEEK_SET);
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auto nread = file_description().read(buffer, m_logical_block_size);
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ASSERT(!nread.is_error());
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ASSERT(nread.value() == m_logical_block_size);
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return true;
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}
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bool BlockBasedFS::raw_write(unsigned index, const UserOrKernelBuffer& buffer)
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{
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u32 base_offset = static_cast<u32>(index) * static_cast<u32>(m_logical_block_size);
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file_description().seek(base_offset, SEEK_SET);
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auto nwritten = file_description().write(buffer, m_logical_block_size);
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ASSERT(!nwritten.is_error());
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ASSERT(nwritten.value() == m_logical_block_size);
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return true;
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}
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bool BlockBasedFS::raw_read_blocks(unsigned index, size_t count, UserOrKernelBuffer& buffer)
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{
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auto current = buffer;
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for (unsigned block = index; block < (index + count); block++) {
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if (!raw_read(block, current))
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return false;
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current = current.offset(logical_block_size());
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}
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return true;
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}
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bool BlockBasedFS::raw_write_blocks(unsigned index, size_t count, const UserOrKernelBuffer& buffer)
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{
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auto current = buffer;
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for (unsigned block = index; block < (index + count); block++) {
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if (!raw_write(block, current))
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return false;
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current = current.offset(logical_block_size());
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}
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return true;
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}
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int BlockBasedFS::write_blocks(unsigned index, unsigned count, const UserOrKernelBuffer& data, bool allow_cache)
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{
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ASSERT(m_logical_block_size);
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#ifdef BBFS_DEBUG
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klog() << "BlockBasedFileSystem::write_blocks " << index << " x" << count;
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#endif
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for (unsigned i = 0; i < count; ++i)
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write_block(index + i, data.offset(i * block_size()), block_size(), 0, allow_cache);
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return 0;
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}
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int BlockBasedFS::read_block(unsigned index, UserOrKernelBuffer* buffer, size_t count, size_t offset, bool allow_cache) const
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{
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ASSERT(m_logical_block_size);
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ASSERT(offset + count <= block_size());
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#ifdef BBFS_DEBUG
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klog() << "BlockBasedFileSystem::read_block " << index;
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#endif
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if (!allow_cache) {
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const_cast<BlockBasedFS*>(this)->flush_specific_block_if_needed(index);
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u32 base_offset = static_cast<u32>(index) * static_cast<u32>(block_size()) + static_cast<u32>(offset);
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file_description().seek(base_offset, SEEK_SET);
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auto nread = file_description().read(*buffer, count);
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if (nread.is_error())
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return -EIO;
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ASSERT(nread.value() == count);
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return 0;
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}
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auto& entry = cache().get(index);
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if (!entry.has_data) {
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u32 base_offset = static_cast<u32>(index) * static_cast<u32>(block_size());
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file_description().seek(base_offset, SEEK_SET);
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auto entry_data_buffer = UserOrKernelBuffer::for_kernel_buffer(entry.data);
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auto nread = file_description().read(entry_data_buffer, block_size());
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if (nread.is_error())
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return -EIO;
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ASSERT(nread.value() == block_size());
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entry.has_data = true;
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}
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if (buffer && !buffer->write(entry.data + offset, count))
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return -EFAULT;
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return 0;
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}
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int BlockBasedFS::read_blocks(unsigned index, unsigned count, UserOrKernelBuffer& buffer, bool allow_cache) const
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{
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ASSERT(m_logical_block_size);
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if (!count)
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return false;
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if (count == 1)
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return read_block(index, &buffer, block_size(), 0, allow_cache);
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auto out = buffer;
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for (unsigned i = 0; i < count; ++i) {
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auto err = read_block(index + i, &out, block_size(), 0, allow_cache);
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if (err < 0)
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return err;
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out = out.offset(block_size());
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}
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return 0;
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}
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void BlockBasedFS::flush_specific_block_if_needed(unsigned index)
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{
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LOCKER(m_lock);
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if (!cache().is_dirty())
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return;
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Vector<CacheEntry*, 32> cleaned_entries;
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cache().for_each_dirty_entry([&](CacheEntry& entry) {
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if (entry.block_index != index) {
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u32 base_offset = static_cast<u32>(entry.block_index) * static_cast<u32>(block_size());
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file_description().seek(base_offset, SEEK_SET);
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// FIXME: Should this error path be surfaced somehow?
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auto entry_data_buffer = UserOrKernelBuffer::for_kernel_buffer(entry.data);
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(void)file_description().write(entry_data_buffer, block_size());
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cleaned_entries.append(&entry);
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}
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});
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// NOTE: We make a separate pass to mark entries clean since marking them clean
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// moves them out of the dirty list which would disturb the iteration above.
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for (auto* entry : cleaned_entries)
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cache().mark_clean(*entry);
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}
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void BlockBasedFS::flush_writes_impl()
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{
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LOCKER(m_lock);
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if (!cache().is_dirty())
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return;
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u32 count = 0;
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cache().for_each_dirty_entry([&](CacheEntry& entry) {
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u32 base_offset = static_cast<u32>(entry.block_index) * static_cast<u32>(block_size());
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file_description().seek(base_offset, SEEK_SET);
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// FIXME: Should this error path be surfaced somehow?
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auto entry_data_buffer = UserOrKernelBuffer::for_kernel_buffer(entry.data);
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(void)file_description().write(entry_data_buffer, block_size());
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++count;
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});
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cache().mark_all_clean();
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dbg() << class_name() << ": Flushed " << count << " blocks to disk";
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}
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void BlockBasedFS::flush_writes()
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{
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flush_writes_impl();
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}
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DiskCache& BlockBasedFS::cache() const
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{
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if (!m_cache)
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m_cache = make<DiskCache>(const_cast<BlockBasedFS&>(*this));
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return *m_cache;
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}
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}
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