On 02/10/20 17:44, Claudio Imbrenda wrote:
The KVM unit tests are increasingly being used to test more than just KVM. They are being used to test TCG, qemu I/O device emulation, other hypervisors, and even actual hardware. The existing memory allocators are becoming more and more inadequate to the needs of the upcoming unit tests (but also some existing ones, see below). Some important features that are lacking: * ability to perform a small physical page allocation with a big alignment withtout wasting huge amounts of memory * ability to allocate physical pages from specific pools/areaas (e.g. below 16M, or 4G, etc) * ability to reserve arbitrary pages (if free), removing them from the free pool Some other features that are nice, but not so fundamental: * no need for the generic allocator to keep track of metadata (i.e. allocation size), this is now handled by the lower level allocators * coalescing small blocks into bigger ones, to allow contiguous memory freed in small blocks in a random order to be used for large allocations again This is achieved in the following ways: For the virtual allocator: * only the virtul allocator needs one extra page of metadata, but only for allocations that wouldn't fit in one page For the page allocator: * page allocator has up to 6 memory pools, each pool has a metadata area; the metadata has a byte for each page in the area, describing the order of the block it belongs to, and whether it is free * if there are no free blocks of the desired size, a bigger block is split until we reach the required size; the unused parts of the block are put back in the free lists * if an allocation needs ablock with a larger alignment than its size, a larger block of (at least) the required order is split; the unused parts put back in the appropriate free lists * if the allocation could not be satisfied, the next allowed area is searched; the allocation fails only when all allowed areas have been tried * new functions to perform allocations from specific areas; the areas are arch-dependent and should be set up by the arch code * for now x86 has a memory area for "lowest" memory under 16MB, one for "low" memory under 4GB and one for the rest, while s390x has one for under 2GB and one for the rest; suggestions for more fine grained areas or for the other architectures are welcome * upon freeing a block, an attempt is made to coalesce it into the appropriate neighbour (if it is free), and so on for the resulting larger block thus obtained For the physical allocator: * the minimum alignment is now handled manually, since it has been removed from the common struct This patchset addresses some current but otherwise unsolvable issues on s390x, such as the need to allocate a block under 2GB for each SMP CPU upon CPU activation. This patchset has been tested on s390x, amd64 and i386. It has also been compiled on aarch64. V1->V2: * Renamed some functions, as per review comments * Improved commit messages * Split the list handling functions into an independent header * Addded arch-specific headers to define the memory areas * Fixed some minor issues * The magic value for small allocations in the virtual allocator is now put right before the returned pointer, like for large allocations * Added comments to make the code more readable * Many minor fixes
Queued with the exception of patch 6 (still waiting for the CI to finish, but still).
Paolo
