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Microsoft allows you to coalesce multiple free placeholders in one VirtualFreeEx call, so we can perform the VirtualFreeEx after coalescing with neighboring regions to eliminate a VirtualFreeEx call in some situations.
This commit is contained in:
Stephen Miller 2026-01-21 21:27:42 -06:00
parent 0d5c5f81a6
commit e451f516d9
1 changed files with 29 additions and 21 deletions
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50
src/core/address_space.cpp
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@ -367,14 +367,19 @@ struct AddressSpace::Impl {
}
}
void* Map(VAddr virtual_addr, PAddr phys_addr, u64 size, ULONG prot, s32 fd = -1) {
// Split surrounding regions to create a placeholder
SplitRegion(virtual_addr, size);
// Get the region this range covers
void* Map(VAddr virtual_addr, PAddr phys_addr, u64 size, ULONG prot, s32 fd = -1,
bool is_shared = false) {
// Get a pointer to the region containing virtual_addr
auto it = std::prev(regions.upper_bound(virtual_addr));
auto& [base, region] = *it;
// If needed, split surrounding regions to create a placeholder
if (it->first != virtual_addr || it->second.size != size) {
SplitRegion(virtual_addr, size);
it = std::prev(regions.upper_bound(virtual_addr));
}
// Get the address and region for this range.
auto& [base, region] = *it;
ASSERT_MSG(!region.is_mapped, "Cannot overwrite mapped region");
// Now we have a region matching the requested region, perform the actual mapping.
@ -391,30 +396,33 @@ struct AddressSpace::Impl {
ASSERT_MSG(!it->second.is_mapped, "Cannot coalesce mapped regions");
// Check if a placeholder exists right before us.
bool can_coalesce = false;
auto it_prev = it != regions.begin() ? std::prev(it) : regions.end();
if (it_prev != regions.end() && !it_prev->second.is_mapped) {
const u64 total_size = it_prev->second.size + it->second.size;
if (!VirtualFreeEx(process, LPVOID(it_prev->first), total_size,
MEM_RELEASE | MEM_COALESCE_PLACEHOLDERS)) {
UNREACHABLE_MSG("Region coalescing failed: {}", Common::GetLastErrorMsg());
}
it_prev->second.size = total_size;
// If there is an earlier region, move our iterator to that and increase size.
it_prev->second.size = it_prev->second.size + it->second.size;
regions.erase(it);
it = it_prev;
// Mark this region as coalesce-able.
can_coalesce = true;
}
// Check if a placeholder exists right after us.
auto it_next = std::next(it);
if (it_next != regions.end() && !it_next->second.is_mapped) {
const u64 total_size = it->second.size + it_next->second.size;
if (!VirtualFreeEx(process, LPVOID(it->first), total_size,
// If there is a later region, increase our current region's size
it->second.size = it->second.size + it_next->second.size;
regions.erase(it_next);
// Mark this region as coalesce-able.
can_coalesce = true;
}
// If there are placeholders to coalesce, then coalesce them.
if (can_coalesce) {
if (!VirtualFreeEx(process, LPVOID(it->first), it->second.size,
MEM_RELEASE | MEM_COALESCE_PLACEHOLDERS)) {
UNREACHABLE_MSG("Region coalescing failed: {}", Common::GetLastErrorMsg());
}
it->second.size = total_size;
regions.erase(it_next);
}
}
@ -423,7 +431,7 @@ struct AddressSpace::Impl {
u64 remaining_size = size;
VAddr current_addr = virtual_addr;
while (remaining_size > 0) {
// Get the region containing our current address.
// Get a pointer to the region containing virtual_addr
auto it = std::prev(regions.upper_bound(current_addr));
// If necessary, split regions to ensure a valid unmap.
@ -432,10 +440,10 @@ struct AddressSpace::Impl {
u64 size_to_unmap = std::min<u64>(it->second.size - base_offset, remaining_size);
if (current_addr != it->second.base || size_to_unmap != it->second.size) {
SplitRegion(current_addr, size_to_unmap);
it = std::prev(regions.upper_bound(current_addr));
}
// Repair the region pointer, as SplitRegion modifies the regions map.
it = std::prev(regions.upper_bound(current_addr));
// Get the address and region corresponding to this range.
auto& [base, region] = *it;
// Unmap the region if it was previously mapped