Since both the parent process and child process hold a reference to the
COW committed set, once the child process exits, the committed COW
pages are effectively leaked, only being slowly re-claimed each time
the parent process writes to one of them, realizing it's no longer
shared, and uncommitting it.
In order to mitigate this we now hold a weak reference the parent
VMObject from which the pages are cloned, and we use it on destruction
when available to drop the reference to the committed set from it as
well.
This commit moves the allocation of the resources required for
AnonymousVMObject from its constructors to its factory functions.
We're making this change to expose the fallibility of the allocation.
We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.
Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)
The default template argument is only used in one place, and it
looks like it was probably just an oversight. The rest of the Kernel
code all uses u8 as the type. So lets make that the default and remove
the unused template argument, as there doesn't seem to be a reason to
allow the size to be customizable.
This makes for nicer handling of errors compared to checking whether a
RefPtr is null. Additionally, this will give way to return different
types of errors in the future.
