zstd: import usptream v1.5.2

2022-10-24T19:12:32+00:00

Updates the kernel's zstd library to v1.5.2, the latest zstd release. The upstream tag it is updated to is `v1.5.2-kernel`, which contains several cherry-picked commits on top of the v1.5.2 release which are required for the kernel update. I will create this tag once the PR is ready to merge, until then reference the temporary upstream branch `v1.5.2-kernel-cherrypicks`. I plan to submit this patch as part of the v6.2 merge window. I've done basic build testing & testing on x86-64, i386, and aarch64. I'm merging these patches into my `zstd-next` branch, which is pulled into `linux-next` for further testing. I've benchmarked BtrFS with zstd compression on a x86-64 machine, and saw these results. Decompression speed is a small win across the board. The lower compression levels 1-4 see both compression speed and compression ratio wins. The higher compression levels see a small compression speed loss and about neutral ratio. I expect the lower compression levels to be used much more heavily than the high compression levels, so this should be a net win. Level CTime DTime Ratio 1 -2.95% -1.1% -0.7% 3 -3.5% -1.2% -0.5% 5 +3.7% -1.0% +0.0% 7 +3.2% -0.9% +0.0% 9 -4.3% -0.8% +0.1% Signed-off-by: Nick Terrell

kernel/linux.git/lib/zstd/compress/clevels.h, branch v6.4

zstd: import usptream v1.5.2