The previous allocator was very naive and kept the state of all pages
in one big bitmap. When allocating, we had to scan through the bitmap
until we found an unset bit.
This patch introduces a new binary buddy allocator that manages the
physical memory pages.
Each PhysicalRegion is divided into zones (PhysicalZone) of 16MB each.
Any extra pages at the end of physical RAM that don't fit into a 16MB
zone are turned into 15 or fewer 1MB zones.
Each zone starts out with one full-sized block, which is then
recursively subdivided into halves upon allocation, until a block of
the request size can be returned.
There are more opportunities for improvement here: the way zone objects
are allocated and stored is non-optimal. Same goes for the allocation
of buddy block state bitmaps.
Instead of each PhysicalPage knowing whether it comes from the
supervisor pages or from the user pages, we can just check in both
sets when freeing a page.
It's just a handful of pointer range checks, nothing expensive.
By making sure the PhysicalPage instance is fully destructed the
allocators will have a chance to reclaim the PhysicalPageEntry for
free-list purposes. Just pass them the physical address of the page
that was freed, which is enough to lookup the PhysicalPageEntry later.
By moving the PhysicalPage classes out of the kernel heap into a static
array, one for each physical page, we can avoid the added overhead and
easily find them by indexing into an array.
This also wraps the PhysicalPage into a PhysicalPageEntry, which allows
us to re-use each slot with information where to find the next free
page.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
(...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.
A 16-bit refcount is just begging for trouble right nowl.
A 32-bit refcount will be begging for trouble later down the line,
so we'll have to revisit this eventually. :^)
As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
This makes no functional difference, but it makes it clear that
MemoryManager and PhysicalRegion take over the actual physical
page represented by this PhysicalPage instance.
Pages created with PhysicalPage::create_eternal() should *not* be
returnable to the freelist; and pages created with the regular
PhysicalPage::create() should be; not the other way around.
This significantly reduces the pressure on the kernel heap when
allocating a lot of pages.
Previously at about 250MB allocated, the free page list would outgrow
the kernel's heap. Given that there is no longer a page list, this does
not happen.
The next barrier will be the kernel memory used by the page records for
in-use memory. This kicks in at about 1GB.
