When constructing an AnonymousVMObject with the AllocateNow allocation
strategy we accidentally allocated the committed pages directly through
MemoryManager instead of taking them from our m_unused_physical_pages
CommittedPhysicalPageSet, which meant they were counted as allocated in
MemoryManager, but were still counted as unallocated in the PageSet,
who would then try to uncommit them on destruction, resulting in a
failed assertion.
To help prevent similar issues in the future a Badge<T> was added to
MM::allocate_committed_user_physical_page to prevent allocation of
commited pages not via a CommittedPhysicalPageSet.
An svg layout element without a `SVGSVGElement` ancestor caused a failed
assertion before, because the svg context does not exist when `paint()`
is called
When it is called inside `box.for_each_child`, then it may not be called
for the root element. By missing `SVGSVGBox::before_children_paint`
the svg context is not created
When we hit a COW fault and discover than no other process is sharing
the physical page, we simply remap it r/w and save ourselves the
trouble. When this happens, we can also give back (uncommit) one of our
shared committed COW pages, since we won't be needing it.
We had this optimization before, but I mistakenly removed it in
50472fd69f since I had misunderstood
it to be the reason for a panic.
We currently overcommit for COW when forking a process and cloning its
memory regions. Both the parent and child process share a set of.
committed COW pages.
If there's COW sharing across more than two processeses within a lineage
(e.g parent, child & grandchild), it's possible to exhaust these pages.
When the shared set is emptied, the next COW fault in each process must
detach from the shared set and fall back to on demand allocation.
This patch makes sure that we detach from the shared set once we
discover it to be empty (during COW fault handling). This fixes an issue
where we'd try to allocate from an exhausted shared set while building
GNU binutils inside SerenityOS.
It was doing a bunch of things it didn't need to do. I think we had
misunderstood the base class as having copied m_lock in its copy
constructor but it's actually default initialized.
We had issues with committed physical pages getting miscounted in some
situations, and instead of figuring out what was going wrong and making
sure all the commits had matching uncommits, this patch makes the
problem go away by adding an RAII class to manage this instead. :^)
MemoryManager::commit_user_physical_pages() now returns an (optional)
CommittedPhysicalPageSet. You can then allocate pages from the page set
by calling take_one() on it. Any unallocated pages are uncommitted upon
destruction of the page set.
This allows running QEMU inside WSL2 for hosts which have nested KVM
and WSLg support (e.g. Windows 11).
Running QEMU inside the WSL2 VM is slightly slower than running QEMU
on Windows, probably because of how WSLg handles screen updates.
