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Kernel: Implement lazy committed page allocation

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By designating a committed page pool we can guarantee to have physical
pages available for lazy allocation in mappings. However, when forking
we will overcommit. The assumption is that worst-case it's better for
the fork to die due to insufficient physical memory on COW access than
the parent that created the region. If a fork wants to ensure that all
memory is available (trigger a commit) then it can use madvise.

This also means that fork now can gracefully fail if we don't have
enough physical pages available.
This commit is contained in:
Tom 2020-09-04 21:12:25 -06:00 • committed by Andreas Kling
parent e21cc4cff6
commit b2a52f6208
20 changed files with 329 additions and 67 deletions
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9
Kernel/Syscalls/fork.cpp
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@ -88,7 +88,14 @@ pid_t Process::sys$fork(RegisterState& regs)
#ifdef FORK_DEBUG
dbg() << "fork: cloning Region{" << &region << "} '" << region.name() << "' @ " << region.vaddr();
#endif
auto& child_region = child->add_region(region.clone());
auto region_clone = region.clone();
if (!region_clone) {
dbg() << "fork: Cannot clone region, insufficient memory";
// TODO: tear down new process?
return -ENOMEM;
}
auto& child_region = child->add_region(region_clone.release_nonnull());
child_region.map(child->page_directory());
if (&region == m_master_tls_region.unsafe_ptr())