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Kernel: Implement a simple virtual address range allocator.

This replaces the previous virtual address allocator which was basically
just "m_next_address += size;"

With this in place, virtual addresses can get reused, which cuts down on
the number of page tables created. When we implement ASLR some day, we'll
probably have to do page table deallocation, but for now page tables are
only deallocated once the process dies.
This commit is contained in:
Andreas Kling 2019-05-17 03:40:15 +02:00
parent c56e3ebee1
commit c414e65498
5 changed files with 231 additions and 22 deletions

View file

@ -0,0 +1,137 @@
#include <Kernel/VM/RangeAllocator.h>
#include <Kernel/kstdio.h>
#include <AK/QuickSort.h>
RangeAllocator::RangeAllocator(LinearAddress base, size_t size)
{
m_available_ranges.append({ base, size });
}
RangeAllocator::~RangeAllocator()
{
}
void RangeAllocator::dump() const
{
dbgprintf("RangeAllocator{%p}\n", this);
for (auto& range : m_available_ranges) {
dbgprintf(" %x -> %x\n", range.base().get(), range.end().get() - 1);
}
}
Vector<Range, 2> Range::carve(const Range& taken)
{
Vector<Range, 2> parts;
if (taken == *this)
return { };
if (taken.base() > base())
parts.append({ base(), taken.base().get() - base().get() });
if (taken.end() < end())
parts.append({ taken.end(), end().get() - taken.end().get() });
#ifdef VRA_DEBUG
dbgprintf("VRA: carve: remaining parts:\n");
for (int i = 0; i < parts.size(); ++i)
dbgprintf(" %x-%x\n", parts[i].base().get(), parts[i].end().get() - 1);
#endif
return parts;
}
void RangeAllocator::carve_at_index(int index, const Range& range)
{
auto remaining_parts = m_available_ranges[index].carve(range);
ASSERT(remaining_parts.size() >= 1);
m_available_ranges[index] = remaining_parts[0];
if (remaining_parts.size() == 2)
m_available_ranges.insert(index + 1, move(remaining_parts[1]));
}
Range RangeAllocator::allocate_anywhere(size_t size)
{
for (int i = 0; i < m_available_ranges.size(); ++i) {
auto& available_range = m_available_ranges[i];
if (available_range.size() < size)
continue;
Range allocated_range(available_range.base(), size);
if (available_range.size() == size) {
#ifdef VRA_DEBUG
dbgprintf("VRA: Allocated perfect-fit anywhere(%u): %x\n", size, allocated_range.base().get());
#endif
m_available_ranges.remove(i);
return allocated_range;
}
carve_at_index(i, allocated_range);
#ifdef VRA_DEBUG
dbgprintf("VRA: Allocated anywhere(%u): %x\n", size, allocated_range.base().get());
dump();
#endif
return allocated_range;
}
kprintf("VRA: Failed to allocate anywhere: %u\n", size);
return { };
}
Range RangeAllocator::allocate_specific(LinearAddress base, size_t size)
{
Range allocated_range(base, size);
for (int i = 0; i < m_available_ranges.size(); ++i) {
auto& available_range = m_available_ranges[i];
if (!available_range.contains(base, size))
continue;
if (available_range == allocated_range) {
m_available_ranges.remove(i);
return allocated_range;
}
carve_at_index(i, allocated_range);
#ifdef VRA_DEBUG
dbgprintf("VRA: Allocated specific(%u): %x\n", size, available_range.base().get());
dump();
#endif
return allocated_range;
}
kprintf("VRA: Failed to allocate specific range: %x(%u)\n", base.get(), size);
return { };
}
void RangeAllocator::deallocate(Range range)
{
#ifdef VRA_DEBUG
dbgprintf("VRA: Deallocate: %x(%u)\n", range.base().get(), range.size());
dump();
#endif
for (auto& available_range : m_available_ranges) {
if (available_range.end() == range.base()) {
available_range.m_size += range.size();
goto sort_and_merge;
}
}
m_available_ranges.append(range);
sort_and_merge:
// FIXME: We don't have to sort if we insert at the right position immediately.
quick_sort(m_available_ranges.begin(), m_available_ranges.end(), [] (auto& a, auto& b) {
return a.base() < b.base();
});
Vector<Range> merged_ranges;
merged_ranges.ensure_capacity(m_available_ranges.size());
for (auto& range : m_available_ranges) {
if (merged_ranges.is_empty()) {
merged_ranges.append(range);
continue;
}
if (range.base() == merged_ranges.last().end()) {
merged_ranges.last().m_size += range.size();
continue;
}
merged_ranges.append(range);
}
m_available_ranges = move(merged_ranges);
#ifdef VRA_DEBUG
dbgprintf("VRA: After deallocate\n");
dump();
#endif
}