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Kernel: Shorten time under spinlocks while handling inode faults

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- Instead of holding the VMObject lock across physical page allocation
  and quick-map + copy, we now only hold it when updating the VMObject's
  physical page slot.
This commit is contained in:
Andreas Kling 2022-08-18 14:43:36 +02:00
parent 03e9697975
commit 45e6123de8
1 changed files with 21 additions and 16 deletions
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37
Kernel/Memory/Region.cpp
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@ -471,11 +471,12 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
auto& inode_vmobject = static_cast<InodeVMObject&>(vmobject());
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
auto& vmobject_physical_page_entry = inode_vmobject.physical_pages()[page_index_in_vmobject];
auto& vmobject_physical_page_slot = inode_vmobject.physical_pages()[page_index_in_vmobject];
{
// NOTE: The VMObject lock is required when manipulating the VMObject's physical page slot.
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_entry.is_null()) {
if (!vmobject_physical_page_slot.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))
return PageFaultResponse::OutOfMemory;
@ -506,9 +507,25 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
memset(page_buffer + nread, 0, PAGE_SIZE - nread);
}
// Allocate a new physical page, and copy the read inode contents into it.
auto new_physical_page_or_error = MM.allocate_physical_page(MemoryManager::ShouldZeroFill::No);
if (new_physical_page_or_error.is_error()) {
dmesgln("MM: handle_inode_fault was unable to allocate a physical page");
return PageFaultResponse::OutOfMemory;
}
auto new_physical_page = new_physical_page_or_error.release_value();
{
// NOTE: The MM lock is required for quick-mapping.
SpinlockLocker mm_locker(s_mm_lock);
u8* dest_ptr = MM.quickmap_page(*new_physical_page);
memcpy(dest_ptr, page_buffer, PAGE_SIZE);
MM.unquickmap_page();
}
// NOTE: The VMObject lock is required when manipulating the VMObject's physical page slot.
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_entry.is_null()) {
if (!vmobject_physical_page_slot.is_null()) {
// 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.");
@ -517,19 +534,7 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
return PageFaultResponse::Continue;
}
auto vmobject_physical_page_or_error = MM.allocate_physical_page(MemoryManager::ShouldZeroFill::No);
if (vmobject_physical_page_or_error.is_error()) {
dmesgln("MM: handle_inode_fault was unable to allocate a physical page");
return PageFaultResponse::OutOfMemory;
}
vmobject_physical_page_entry = vmobject_physical_page_or_error.release_value();
{
SpinlockLocker mm_locker(s_mm_lock);
u8* dest_ptr = MM.quickmap_page(*vmobject_physical_page_entry);
memcpy(dest_ptr, page_buffer, PAGE_SIZE);
MM.unquickmap_page();
}
vmobject_physical_page_slot = move(new_physical_page);
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;