This may seem like a no-op change, however it shrinks down the Kernel by a bit:
.text -432
.unmap_after_init -60
.data -480
.debug_info -673
.debug_aranges 8
.debug_ranges -232
.debug_line -558
.debug_str -308
.debug_frame -40
With '= default', the compiler can do more inlining, hence the savings.
I intentionally omitted some opportunities for '= default', because they
would increase the Kernel size.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
When the ExpandableHeap calls the remove_memory function, the
subheap is assumed to be removed and freed entirely. remove_memory
may drop the underlying memory at any time, but it also may cause
further allocation requests. Not removing it from the list before
calling remove_memory could cause a memory allocation in that
subheap while remove_memory is executing. which then causes issues
once the underlying memory is actually freed.
By being a bit too greedy and only allocating how much we need for
the failing allocation, we can end up in an infinite loop trying
to expand the heap further. That's because there are other allocations
(e.g. logging, vmobjects, regions, ...) that happen before we finally
retry the failed allocation request.
Also fix allocating in page size increments, which lead to an assertion
when the heap had to grow more than the 1 MiB backup.
The process of expanding memory requires allocations and deallocations
on the heap itself. So, while we're trying to expand the heap, don't
remove memory just because we might briefly not need it. Also prevent
recursive expansion attempts.
Add an ExpandableHeap and switch kmalloc to use it, which allows
for the kmalloc heap to grow as needed.
In order to make heap expansion to work, we keep around a 1 MiB backup
memory region, because creating a region would require space in the
same heap. This means, the heap will grow as soon as the reported
utilization is less than 1 MiB. It will also return memory if an entire
subheap is no longer needed, although that is rarely possible.
