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memory: copy sparse backing in one traversal

This commit is contained in:
nmzik 2026-10-07 23:17:53 +04:00
parent 7e011fa565
commit 45b6d2c597
2 changed files with 24 additions and 16 deletions
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22
src/kernel/memoryAddressSpace.inc
View File

@ -258,28 +258,18 @@ public:
g_test_backing_read(vaddr, size);
}
#endif
const auto end = vaddr + size;
auto first = m_maps.lower_bound(vaddr);
if (first != m_maps.begin()) {
auto previous = std::prev(first);
const auto end = vaddr + size;
auto mapping = m_maps.lower_bound(vaddr);
if (mapping != m_maps.begin()) {
auto previous = std::prev(mapping);
if (previous->second.vaddr + previous->second.size > vaddr) {
first = previous;
}
}
for (auto mapping = first; mapping != m_maps.end() && mapping->second.vaddr < end;
++mapping) {
const auto& entry = mapping->second;
const auto start = std::max(vaddr, entry.vaddr);
const auto bytes = std::min(end, entry.vaddr + entry.size) - start;
if (!RangeOk(entry.backing_offset + start - entry.vaddr, bytes)) {
return false;
mapping = previous;
}
}
auto* destination = static_cast<uint8_t*>(data);
auto cursor = vaddr;
for (auto mapping = first; mapping != m_maps.end() && mapping->second.vaddr < end;
++mapping) {
for (; mapping != m_maps.end() && mapping->second.vaddr < end; ++mapping) {
const auto& entry = mapping->second;
const auto start = std::max(vaddr, entry.vaddr);
const auto bytes = std::min(end, entry.vaddr + entry.size) - start;

18
tests/VirtualMemoryAllocationTests.cpp
View File

@ -465,6 +465,24 @@ void TestSparseBackingReadPreservesResidency() {
std::all_of(bytes.begin() + commit_size * 2, bytes.end(),
[](uint8_t value) { return value == 0xa7; }),
"sparse backing read did not copy resident pages and zero nonresident pages");
constexpr size_t prefix = 37, suffix = 53;
constexpr size_t clipped_size = prefix + commit_size + suffix;
std::fill(bytes.begin(), bytes.end(), 0x5a);
Check(test,
Libs::LibKernel::Memory::TryReadSparseBacking(
base + commit_size - prefix, bytes.data() + 1, clipped_size),
"sparse backing read rejected unaligned resident edges around a hole");
Check(test, bytes.front() == 0x5a && bytes[clipped_size + 1] == 0x5a,
"clipped sparse backing read overwrote destination canaries");
Check(test,
std::all_of(bytes.begin() + 1, bytes.begin() + 1 + prefix,
[](uint8_t value) { return value == 0x3c; }) &&
std::all_of(bytes.begin() + 1 + prefix, bytes.begin() + 1 + prefix + commit_size,
[](uint8_t value) { return value == 0; }) &&
std::all_of(bytes.begin() + 1 + prefix + commit_size,
bytes.begin() + 1 + clipped_size,
[](uint8_t value) { return value == 0xa7; }),
"clipped sparse backing read misplaced resident bytes or the intervening hole");
std::fill(bytes.begin(), bytes.end(), 0x5a);
Check(test, Libs::LibKernel::Memory::TryReadSparseBacking(base + commit_size, bytes.data(),
bytes.size()),