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Kernel: Only update page tables for faulting region

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When a page fault led to the mapping of a new physical page, we were
updating the page tables for *every* region that shared the same
underlying VMObject.

Let's just not do that, avoiding a bunch of unnecessary page table
updates and TLB invalidations.
This commit is contained in:
Andreas Kling 2022-02-02 00:51:45 +01:00
parent 4389c7de25
commit 1c5ffaae41
Notes: sideshowbarker 2024-07-17 19:53:11 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/1c5ffaae41b
2 changed files with 11 additions and 29 deletions
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37
Kernel/Memory/Region.cpp
View File

@ -220,33 +220,18 @@ bool Region::map_individual_page_impl(size_t page_index)
return true;
}
bool Region::do_remap_vmobject_page(size_t page_index, bool with_flush)
bool Region::remap_individual_page(size_t page_index, ShouldFlushTLB should_flush_tlb)
{
if (!m_page_directory)
return true; // not an error, region may have not yet mapped it
if (!translate_vmobject_page(page_index))
return true; // not an error, region doesn't map this page
VERIFY(m_page_directory);
SpinlockLocker page_lock(m_page_directory->get_lock());
SpinlockLocker lock(s_mm_lock);
VERIFY(physical_page(page_index));
bool success = map_individual_page_impl(page_index);
if (with_flush)
if (should_flush_tlb == ShouldFlushTLB::Yes)
MemoryManager::flush_tlb(m_page_directory, vaddr_from_page_index(page_index));
return success;
}
bool Region::remap_vmobject_page(size_t page_index, bool with_flush)
{
auto& vmobject = this->vmobject();
bool success = true;
SpinlockLocker lock(vmobject.m_lock);
vmobject.for_each_region([&](auto& region) {
if (!region.do_remap_vmobject_page(page_index, with_flush))
success = false;
});
return success;
}
void Region::unmap(ShouldDeallocateVirtualRange should_deallocate_range, ShouldFlushTLB should_flush_tlb)
{
if (!m_page_directory)
@ -358,10 +343,9 @@ PageFaultResponse Region::handle_fault(PageFault const& fault)
auto& page_slot = physical_page_slot(page_index_in_region);
if (page_slot->is_lazy_committed_page()) {
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
VERIFY(m_vmobject->is_anonymous());
page_slot = static_cast<AnonymousVMObject&>(*m_vmobject).allocate_committed_page({});
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_individual_page(page_index_in_region))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -388,13 +372,12 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
VERIFY(vmobject().is_anonymous());
auto& page_slot = physical_page_slot(page_index_in_region);
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
SpinlockLocker locker(vmobject().m_lock);
if (!page_slot.is_null() && !page_slot->is_shared_zero_page() && !page_slot->is_lazy_committed_page()) {
dbgln_if(PAGE_FAULT_DEBUG, "MM: zero_page() but page already present. Fine with me!");
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_individual_page(page_index_in_region))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -417,7 +400,7 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
dbgln_if(PAGE_FAULT_DEBUG, " >> ALLOCATED {}", page_slot->paddr());
}
if (!remap_vmobject_page(page_index_in_vmobject)) {
if (!remap_individual_page(page_index_in_region)) {
dmesgln("MM: handle_zero_fault was unable to allocate a page table to map {}", page_slot);
return PageFaultResponse::OutOfMemory;
}
@ -436,7 +419,7 @@ PageFaultResponse Region::handle_cow_fault(size_t page_index_in_region)
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
auto response = reinterpret_cast<AnonymousVMObject&>(vmobject()).handle_cow_fault(page_index_in_vmobject, vaddr().offset(page_index_in_region * PAGE_SIZE));
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_individual_page(page_index_in_region))
return PageFaultResponse::OutOfMemory;
return response;
}
@ -457,7 +440,7 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_entry.is_null()) {
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else before reading, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_individual_page(page_index_in_region))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -492,7 +475,7 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
// Someone else faulted in this page while we were reading from the inode.
// No harm done (other than some duplicate work), remap the page here and return.
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_individual_page(page_index_in_region))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
@ -511,7 +494,7 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
MM.unquickmap_page();
}
if (!remap_vmobject_page(page_index_in_vmobject))
if (!remap_individual_page(page_index_in_region))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;

3
Kernel/Memory/Region.h
View File

@ -196,8 +196,7 @@ public:
private:
Region(VirtualRange const&, NonnullRefPtr<VMObject>, size_t offset_in_vmobject, OwnPtr<KString>, Region::Access access, Cacheable, bool shared);
[[nodiscard]] bool remap_vmobject_page(size_t page_index, bool with_flush = true);
[[nodiscard]] bool do_remap_vmobject_page(size_t page_index, bool with_flush = true);
[[nodiscard]] bool remap_individual_page(size_t page_index, ShouldFlushTLB = ShouldFlushTLB::Yes);
void set_access_bit(Access access, bool b)
{