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Remove Box from RcSlice #51281
referenced this pull request
Jun 1, 2018
added a commit
this pull request
Jun 6, 2018
@nnethercote This does seem to be a regression in wall time and memory usage.. https://perf.rust-lang.org/compare.html?start=685faa2c3ee062aaf30ddf6d3daf4ef3b576979b&end=d9589e4c2db96769a2be22f29625cb31266557cc&stat=max-rss. I guess maybe we shouldn't land this? Is your interpretation different?
I took a look at deep-vector and regex with Cachegrind and DHAT. deep-vector because it showed the big regression, and regex because DHAT shows its the benchmark that has the highest proportion of these RcSlice allocations.
DHAT agrees that the max RSS does increase significantly for deep-vector. (I get a 16% increase on a clean-check build.) Presumably because we end up having two copies of the data live while copying from the Vector to the slice.
Other than that, there's not much change -- regex is hardly affected -- and no clear benefit. The total number of allocations done doesn't change. Instruction counts don't change.
It's a shame, but I agree that this shouldn't be landed.