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Ext2FS: allocate_blocks allocates contiguous blocks (#1095)

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This implementation uses the new helper method of Bitmap called
find_longest_range_of_unset_bits. This method looks for the biggest 
range of contiguous bits unset in the bitmap and returns the start of
the range back to the caller.
This commit is contained in:
Marios Prokopakis 2020-01-26 10:48:24 +02:00 committed by Andreas Kling
parent d847368c88
commit da296f5865
2 changed files with 81 additions and 5 deletions
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41
AK/Bitmap.h
View File

@ -157,6 +157,46 @@ public:
return -1;
}
int find_longest_range_of_unset_bits(int max_length, int& found_range_size) const
{
int first_index = find_first_unset();
if (first_index == -1)
return -1;
int free_region_start = first_index;
int free_region_size = 1;
int max_region_start = free_region_start;
int max_region_size = free_region_size;
// Let's try and find the best fit possible
for (int j = first_index + 1; j < m_size && free_region_size < max_length; j++) {
if (!get(j)) {
if (free_region_size == 0)
free_region_start = j;
free_region_size++;
} else {
if (max_region_size < free_region_size) {
max_region_size = free_region_size;
max_region_start = free_region_start;
}
free_region_start = 0;
free_region_size = 0;
}
}
if (max_region_size < free_region_size) {
max_region_size = free_region_size;
max_region_start = free_region_start;
}
found_range_size = max_region_size;
if (max_region_size > 1)
return max_region_start;
// if the max free region size is one, then return the earliest one found
return first_index;
}
explicit Bitmap()
: m_size(0)
, m_owned(true)
@ -181,7 +221,6 @@ public:
}
private:
int size_in_bytes() const { return ceil_div(m_size, 8); }
u8* m_data { nullptr };

45
Kernel/FileSystem/Ext2FileSystem.cpp
View File

@ -1080,12 +1080,49 @@ Vector<Ext2FS::BlockIndex> Ext2FS::allocate_blocks(GroupIndex preferred_group_in
dbg() << "Ext2FS: allocate_blocks:";
#endif
blocks.ensure_capacity(count);
for (int i = 0; i < count; ++i) {
auto block_index = allocate_block(preferred_group_index);
blocks.unchecked_append(block_index);
bool found_a_group = false;
GroupIndex group_index = preferred_group_index;
if (!group_descriptor(preferred_group_index).bg_free_blocks_count) {
group_index = 1;
}
while (blocks.size() < count) {
if (group_descriptor(group_index).bg_free_blocks_count) {
found_a_group = true;
} else {
if (group_index == preferred_group_index)
group_index = 1;
for (; group_index < m_block_group_count; ++group_index) {
if (group_descriptor(group_index).bg_free_blocks_count) {
found_a_group = true;
break;
}
}
}
ASSERT(found_a_group);
auto& bgd = group_descriptor(group_index);
auto& cached_bitmap = get_bitmap_block(bgd.bg_block_bitmap);
int blocks_in_group = min(blocks_per_group(), super_block().s_blocks_count);
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 free_region_size = 0;
int first_unset_bit_index = block_bitmap.find_longest_range_of_unset_bits(count - blocks.size(), free_region_size);
ASSERT(first_unset_bit_index != -1);
#ifdef EXT2_DEBUG
dbg() << " > " << block_index;
dbg() << "Ext2FS: allocating free region of size: " << free_region_size << "[" << group_index << "]";
#endif
for (int i = 0; i < free_region_size; ++i) {
BlockIndex block_index = (unsigned)(first_unset_bit_index + i) + first_block_in_group;
set_block_allocation_state(block_index, true);
blocks.unchecked_append(block_index);
#ifdef EXT2_DEBUG
dbg() << " allocated > " << block_index;
#endif
}
}
ASSERT(blocks.size() == count);