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Ext2FS: Cache block bitmaps instead of always reading/writing disk

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Add a simple cache to Ext2FS where we keep block bitmaps along with a
dirty bit. This allows us to coalesce bitmap flushes, giving us a nice
~3x improvement in disk_benchmark write speeds.
This commit is contained in:
Andreas Kling 2019-11-02 12:18:43 +01:00
parent 3a8b5b405c
commit 1ae9d85de9
2 changed files with 52 additions and 19 deletions
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54
Kernel/FileSystem/Ext2FileSystem.cpp
View file

@ -502,6 +502,15 @@ void Ext2FS::flush_writes()
flush_block_group_descriptor_table();
m_block_group_descriptors_dirty = false;
}
for (auto& cached_bitmap : m_cached_bitmaps) {
if (cached_bitmap->dirty) {
write_block(cached_bitmap->bitmap_block_index, cached_bitmap->buffer.data());
cached_bitmap->dirty = false;
#ifdef EXT2_DEBUG
dbg() << "Flushed bitmap block " << cached_bitmap->bitmap_block_index;
#endif
}
}
DiskBackedFS::flush_writes();
}
@ -1006,11 +1015,11 @@ Ext2FS::BlockIndex Ext2FS::allocate_block(GroupIndex preferred_group_index)
}
ASSERT(found_a_group);
auto& bgd = group_descriptor(group_index);
auto& cached_bitmap = get_block_bitmap(bgd.bg_block_bitmap);
auto bitmap_block = ByteBuffer::create_uninitialized(block_size());
read_block(bgd.bg_block_bitmap, bitmap_block.data());
int blocks_in_group = min(blocks_per_group(), super_block().s_blocks_count);
auto block_bitmap = Bitmap::wrap(bitmap_block.data(), blocks_in_group);
auto block_bitmap = Bitmap::wrap(cached_bitmap.buffer.data(), blocks_in_group);
BlockIndex first_block_in_group = (group_index - 1) * blocks_per_group() + first_block_index();
int first_unset_bit_index = block_bitmap.find_first_unset();
ASSERT(first_unset_bit_index != -1);
@ -1200,29 +1209,37 @@ Ext2FS::BlockIndex Ext2FS::first_block_index() const
return block_size() == 1024 ? 1 : 0;
}
Ext2FS::CachedBitmap& Ext2FS::get_block_bitmap(BlockIndex bitmap_block_index)
{
for (auto& cached_bitmap : m_cached_bitmaps) {
if (cached_bitmap->bitmap_block_index == bitmap_block_index)
return *cached_bitmap;
}
auto block = ByteBuffer::create_uninitialized(block_size());
bool success = read_block(bitmap_block_index, block.data());
ASSERT(success);
m_cached_bitmaps.append(make<CachedBitmap>(bitmap_block_index, move(block)));
return *m_cached_bitmaps.last();
}
bool Ext2FS::set_block_allocation_state(BlockIndex block_index, bool new_state)
{
LOCKER(m_lock);
#ifdef EXT2_DEBUG
dbgprintf("Ext2FS: set_block_allocation_state(block=%u, state=%u)\n", block_index, new_state);
#endif
unsigned group_index = group_index_from_block_index(block_index);
GroupIndex group_index = group_index_from_block_index(block_index);
auto& bgd = group_descriptor(group_index);
BlockIndex index_in_group = (block_index - first_block_index()) - ((group_index - 1) * blocks_per_group());
unsigned bit_index = index_in_group % blocks_per_group();
auto& cached_bitmap = get_block_bitmap(bgd.bg_block_bitmap);
bool current_state = cached_bitmap.bitmap(blocks_per_group()).get(bit_index);
#ifdef EXT2_DEBUG
dbgprintf(" index_in_group: %u\n", index_in_group);
dbgprintf(" blocks_per_group: %u\n", blocks_per_group());
dbgprintf(" bit_index: %u\n", bit_index);
dbgprintf(" read_block(%u)\n", bgd.bg_block_bitmap);
#endif
auto block = ByteBuffer::create_uninitialized(block_size());
bool success = read_block(bgd.bg_block_bitmap, block.data());
ASSERT(success);
auto bitmap = Bitmap::wrap(block.data(), blocks_per_group());
bool current_state = bitmap.get(bit_index);
#ifdef EXT2_DEBUG
dbgprintf("Ext2FS: block %u state: %u -> %u\n", block_index, current_state, new_state);
dbgprintf("Ext2FS: block %u state: %u -> %u (in bitmap block %u)\n", block_index, current_state, new_state, bgd.bg_block_bitmap);
#endif
if (current_state == new_state) {
@ -1230,9 +1247,8 @@ bool Ext2FS::set_block_allocation_state(BlockIndex block_index, bool new_state)
return true;
}
bitmap.set(bit_index, new_state);
success = write_block(bgd.bg_block_bitmap, block.data());
ASSERT(success);
cached_bitmap.bitmap(blocks_per_group()).set(bit_index, new_state);
cached_bitmap.dirty = true;
// Update superblock
#ifdef EXT2_DEBUG