Added more consistency checking to the slab allocator, which is built if DEBUG is defined in "stdlib_slab.c".
Memory allocations are no longer guaranteed to be aligned to 64 bit word boundaries. In fact, this has not even worked reliably in the past 10 years.
Memory allocation request sizes are now rounded to multiples of 32 bit words (the size of an address pointer) instead to the size of a 64 bit word.
Reduced the memory footprint of the memory allocation management data structures by reusing the most significant bit of the memory allocation size. This allows many more allocations to fit into the 32 byte chunk slabs, but limits the maximum memory allocation size to a little less than 2 GBytes.
Added integer overflow checks to the memory management code.
Reduced the memory management overhead further. This cuts an additional 8 bytes per allocation, unless neither the slab allocator nor memory pools are available. With this reduction the slab allocator is able to use 16 byte chunks, which cover memory allocation requests of 1..8 bytes.
Fixed a bug caused by returning an allocation back to a slab which passed the wrong pointer.
If the first slab in the list of slabs which share the same chunk size has no more room, it means that all other slabs following it have no room either. This speeds up the test to find a slab with free space, which can now abort and directly proceed to allocate memory for a new slab.
If an empty slab's decay count hits zero, it is moved to the front of the empty slab list to be reclaimed more quickly.
Allocations made from the slab now carry a pointer back to the slab which they are a part of. This speeds up deallocation but has the downside of making the smallest usable slab chunk size 64 bytes, which is double what used to be the minimum before.
The maximum slab size is now 2^17 bytes (= 131072). If you request a slab size larger than this, you will get slab sizes of 131072 bytes instead.
Enabling the memory management debugging code no longer produces compiler errors.
If a new slab is allocated, or an empty slab is reused, the list of empty slabs is now purged, if possible. Empty slabs which cannot be immediately purged "decay" and will be collected the next time a new slab is allocated or an empty slab is reused.
If a chunk is allocated and the slab which the chunk came from is fully utilized, the slab is moved to the end of its list. This should avoid searching this slab for free space before all other slabs of the same chunk size have been tested first. Slabs with free space are always placed closer to the head of the list.
A slab-allocator can now be used as the back-end for all memory allocations by setting __slab_max_size to a value > 0. This controls the slab size used for allocations and should be a power of 2, such as 2048 or 4096 bytes.
This change still needs testing.
Changes in the naming of certain dos.library functions in the
V53 header files are now accounted for. This also affects
unistd/stat/utime code which uses the same header file.
Olaf Barthel