en Copyright 2015 Java http://172.16.0.5:8080/history/llvm-project-15.0.7/compiler-rt/lib/scudo/standalone/tools/compute_size_class_config.cpp#ebff66be [scudo] [standalone] [NFC] clang-format code.clang-format the scudo standalone codebase.Reviewed By: cryptoadDifferential Revision: https://reviews.llvm.org/D93056 List of files: /llvm-project-15.0.7/compiler-rt/lib/scudo/standalone/tools/compute_size_class_config.cpp Thu, 10 Dec 2020 20:16:45 +0000 Mitch Phillips <31459023+hctim@users.noreply.github.com> http://172.16.0.5:8080/history/llvm-project-15.0.7/compiler-rt/lib/scudo/standalone/tools/compute_size_class_config.cpp#041547eb scudo: Table driven size classes for Android allocator.Add an optional table lookup after the existing logarithm computationfor MidSize < Size <= MaxSize during size -> class lookups. The lookup isO(1) due to indexing a precomputed (via constexpr) table based on a sizetable. Switch to this approach for the Android size class maps.Other approaches considered:- Binary search was found to have an unacceptable (~30%) performance cost.- An approach using NEON instructions (see older version of D73824) was found to be slightly slower than this approach on newer SoCs but significantly slower on older ones.By selecting the values in the size tables to minimize wastage (for example,by passing the malloc_info output of a target program to the includedcompute_size_class_config program), we can increase the density of allocationsat a small (~0.5% on bionic malloc_sql_trace as measured using an identitytable) performance cost.Reduces RSS on specific Android processes as follows (KB): Before Afterzygote (median of 50 runs) 26836 26792 (-0.2%)zygote64 (median of 50 runs) 30384 30076 (-1.0%)dex2oat (median of 3 runs) 375792 372952 (-0.8%)I also measured the amount of whole-system idle dirty heap on Android byrebooting the system and then running the following script repeatedly untilthe results were stable:for i in $(seq 1 50); do grep -A5 scudo: /proc/*/smaps | grep Pss: | cut -d: -f2 | awk '{s+=$1} END {print s}' ; sleep 1; doneI did this 3 times both before and after this change and the results were:Before: 365650, 356795, 372663After: 344521, 356328, 342589These results are noisy so it is hard to make a definite conclusion, butthere does appear to be a significant effect.On other platforms, increase the sizes of all size classes by a fixed offsetequal to the size of the allocation header. This has also been found to improvedensity, since it is likely for allocation sizes to be a power of 2, whichwould otherwise waste space by pushing the allocation into the next size class.Differential Revision: https://reviews.llvm.org/D73824 List of files: /llvm-project-15.0.7/compiler-rt/lib/scudo/standalone/tools/compute_size_class_config.cpp Wed, 05 Feb 2020 03:50:25 +0000 Peter Collingbourne <peter@pcc.me.uk>