When we switched the Bitmap code to operating 32 bits at a time,
we neglected to look in the trailing remainder bits after the last
full 32-bit word.
This patch fixes that and adds a couple of tests for Bitmap that I
hacked up while tracking down this bug.
I found this bug when noticing that the kernel would OOM while there
were still some pages left in the physical page allocator.
AK::Bitmap is extended with find_next_range_of_unset_bits().
The function is implemented using count_trailing_zeroes_32(), which is
optimized on many platforms, that gives a huge performance boost.
Functions find_longest_range_of_unset_bits() and find_first_fit() are
implemented with find_next_range_of_unset_bits(). According to
benchmarks, they are 60-100% faster.
We can use __builtin_memset() without including <string.h>.
This is pretty neat, as it will allow us to reduce the header deps
of AK templates a bit, if applied consistently.
Note that this is an enabling change for an upcoming #include removal.
This was causing some obvious-in-hindsight but hard to spot bugs where
we'd implicitly convert the bool to an integer type and carry on with
the number 1 instead of the actual value().
This implementation uses the new helper method of Bitmap called
find_longest_range_of_unset_bits. This method looks for the biggest
range of contiguous bits unset in the bitmap and returns the start of
the range back to the caller.
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.
Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.
sys$fork() now clones all writable regions with per-page COW bits.
The pages are then mapped read-only and we handle a PF by COWing the pages.
This is quite delightful. Obviously there's lots of work to do still,
and it needs better data structures, but the general concept works.
