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Kernel: Optimize FileBackedRegion CoW

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Just copy data from the existing page instead of locking inode's shared
data, copying to temporary buffer and finally copying to destination
This commit is contained in:
Bananymous
2026-05-06 14:59:57 +03:00
parent 62f5292f38
commit 3ac955714b
1 changed files with 9 additions and 21 deletions
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30
kernel/kernel/Memory/FileBackedRegion.cpp
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@@ -106,7 +106,7 @@ namespace Kernel
LockGuard _(m_shared_data->mutex);
for (vaddr_t page_addr = first_page; page_addr < last_page; page_addr += PAGE_SIZE)
if (contains(page_addr))
m_shared_data->sync((page_addr - m_vaddr) / PAGE_SIZE);
m_shared_data->sync((m_offset + page_addr - m_vaddr) / PAGE_SIZE);
return {};
}
@@ -135,17 +135,17 @@ namespace Kernel
return BAN::Error::from_errno(ENOMEM);
const size_t offset = (vaddr - m_vaddr) + m_offset;
ASSERT(offset % 4096 == 0);
ASSERT(offset % PAGE_SIZE == 0);
const size_t bytes = BAN::Math::min<size_t>(m_inode->size() - offset, PAGE_SIZE);
memset(m_shared_data->page_buffer, 0x00, PAGE_SIZE);
TRY(m_inode->read(offset, BAN::ByteSpan(m_shared_data->page_buffer, bytes)));
shared_data_has_correct_page = true;
memset(m_shared_data->page_buffer + bytes, 0, PAGE_SIZE - bytes);
PageTable::with_fast_page(m_shared_data->pages[shared_page_index], [&] {
memcpy(PageTable::fast_page_as_ptr(), m_shared_data->page_buffer, PAGE_SIZE);
});
shared_data_has_correct_page = true;
}
if (m_type == Type::PRIVATE && wants_write)
@@ -176,29 +176,17 @@ namespace Kernel
}
else
{
// page does not need remappings
if (m_type != Type::PRIVATE || !wants_write)
return false;
ASSERT(writable());
// page is already mapped as writable
if (m_page_table.get_page_flags(vaddr) & PageTable::Flags::ReadWrite)
return false;
ASSERT(m_type == Type::PRIVATE && wants_write);
const paddr_t paddr = Heap::get().take_free_page();
if (paddr == 0)
return BAN::Error::from_errno(ENOMEM);
ASSERT(m_shared_data);
LockGuard _(m_shared_data->mutex);
ASSERT(m_shared_data->pages[shared_page_index]);
ASSERT(&m_page_table == &PageTable::current());
PageTable::with_fast_page(paddr, [vaddr] {
memcpy(PageTable::fast_page_as_ptr(), reinterpret_cast<void*>(vaddr), PAGE_SIZE);
});
PageTable::with_fast_page(m_shared_data->pages[shared_page_index], [&] {
memcpy(m_shared_data->page_buffer, PageTable::fast_page_as_ptr(), PAGE_SIZE);
});
PageTable::with_fast_page(paddr, [&] {
memcpy(PageTable::fast_page_as_ptr(), m_shared_data->page_buffer, PAGE_SIZE);
});
m_dirty_pages[local_page_index] = paddr;
m_page_table.map_page_at(paddr, vaddr, m_flags);
}