drm/ttm: new TT backend allocation pool v3
This replaces the spaghetti code in the two existing page pools. First of all depending on the allocation size it is between 3 (1GiB) and 5 (1MiB) times faster than the old implementation. It makes better use of buddy pages to allow for larger physical contiguous allocations which should result in better TLB utilization at least for amdgpu. Instead of a completely braindead approach of filling the pool with one CPU while another one is trying to shrink it we only give back freed pages. This also results in much less locking contention and a trylock free MM shrinker callback, so we can guarantee that pages are given back to the system when needed. Downside of this is that it takes longer for many small allocations until the pool is filled up. We could address this, but I couldn't find an use case where this actually matters. We also don't bother freeing large chunks of pages any more since the CPU overhead in that path isn't really that important. The sysfs files are replaced with a single module parameter, allowing users to override how many pages should be globally pooled in TTM. This unfortunately breaks the UAPI slightly, but as far as we know nobody ever depended on this. Zeroing memory coming from the pool was handled inconsistently. The alloc_pages() based pool was zeroing it, the dma_alloc_attr() based one wasn't. For now the new implementation isn't zeroing pages from the pool either and only sets the __GFP_ZERO flag when necessary. The implementation has only 768 lines of code compared to the over 2600 of the old one, and also allows for saving quite a bunch of code in the drivers since we don't need specialized handling there any more based on kernel config. Additional to all of that there was a neat bug with IOMMU, coherent DMA mappings and huge pages which is now fixed in the new code as well. v2: make ttm_pool_apply_caching static as reported by the kernel bot, add some more checks v3: fix some more checkpatch.pl warnings Signed-off-by:Christian König <christian.koenig@amd.com> Reviewed-by:
Dave Airlie <airlied@redhat.com> Reviewed-by:
Madhav Chauhan <madhav.chauhan@amd.com> Tested-by:
Huang Rui <ray.huang@amd.com> Link: https://patchwork.freedesktop.org/patch/397080/?series=83051&rev=1
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