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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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4
Kernel/Process.cpp
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@ -145,7 +145,9 @@ Region* Process::allocate_region(const Range& range, const String& name, int pro
{
ASSERT(range.is_valid());
auto vmobject = PurgeableVMObject::create_with_size(range.size());
auto region = Region::create_user_accessible(this, range, vmobject, 0, name, prot_to_region_access_flags(prot));
if (!vmobject)
return nullptr;
auto region = Region::create_user_accessible(this, range, vmobject.release_nonnull(), 0, name, prot_to_region_access_flags(prot));
if (!region->map(page_directory()))
return nullptr;
if (should_commit && region->can_commit() && !region->commit())