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Kernel: Release page tables when no longer needed

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When unmapping regions, check if page tables can be freed.

This is a follow-up change for #3254.
This commit is contained in:
Tom 2020-08-27 21:29:17 -06:00 • committed by Andreas Kling
parent 88319b188e
commit 67dbb56444
5 changed files with 50 additions and 7 deletions
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44
Kernel/VM/MemoryManager.cpp
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@ -188,7 +188,7 @@ void MemoryManager::parse_memory_map()
ASSERT(m_user_physical_pages > 0);
}
const PageTableEntry* MemoryManager::pte(const PageDirectory& page_directory, VirtualAddress vaddr)
PageTableEntry* MemoryManager::pte(const PageDirectory& page_directory, VirtualAddress vaddr)
{
ASSERT_INTERRUPTS_DISABLED();
ASSERT(s_mm_lock.own_lock());
@ -227,13 +227,53 @@ PageTableEntry& MemoryManager::ensure_pte(PageDirectory& page_directory, Virtual
pde.set_present(true);
pde.set_writable(true);
pde.set_global(&page_directory == m_kernel_page_directory.ptr());
auto result = page_directory.m_physical_pages.set(move(page_table));
// Use page_directory_table_index and page_directory_index as key
// This allows us to release the page table entry when no longer needed
auto result = page_directory.m_page_tables.set(vaddr.get() & ~0x1fffff, move(page_table));
ASSERT(result == AK::HashSetResult::InsertedNewEntry);
}
return quickmap_pt(PhysicalAddress((FlatPtr)pde.page_table_base()))[page_table_index];
}
void MemoryManager::release_pte(PageDirectory& page_directory, VirtualAddress vaddr, bool is_last_release)
{
ASSERT_INTERRUPTS_DISABLED();
ASSERT(s_mm_lock.own_lock());
u32 page_directory_table_index = (vaddr.get() >> 30) & 0x3;
u32 page_directory_index = (vaddr.get() >> 21) & 0x1ff;
u32 page_table_index = (vaddr.get() >> 12) & 0x1ff;
auto* pd = quickmap_pd(page_directory, page_directory_table_index);
PageDirectoryEntry& pde = pd[page_directory_index];
if (pde.is_present()) {
auto* page_table = quickmap_pt(PhysicalAddress((FlatPtr)pde.page_table_base()));
auto& pte = page_table[page_table_index];
pte.clear();
if (is_last_release || page_table_index == 0x1ff) {
// If this is the last PTE in a region or the last PTE in a page table then
// check if we can also release the page table
bool all_clear = true;
for (u32 i = 0; i <= 0x1ff; i++) {
if (!page_table[i].is_null()) {
all_clear = false;
break;
}
}
if (all_clear) {
pde.clear();
auto result = page_directory.m_page_tables.remove(vaddr.get() & ~0x1fffff);
ASSERT(result);
#ifdef MM_DEBUG
dbg() << "MM: Released page table for " << VirtualAddress(vaddr.get() & ~0x1fffff);
#endif
}
}
}
}
void MemoryManager::initialize(u32 cpu)
{
auto mm_data = new MemoryManagerData;