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7b73e2824b
`futures_lite::AsyncReadExt::read_to_string` (that we use in `RealFs::load`) explicitly does not allocate memory for String contents up front, which leads to excessive reallocations. That reallocation time is a significant contributor to the time we spend loading files (esp large ones). For example, out of ~1s that it takes to open up a 650Mb ASCII buffer on my machine (after changes related to fingerprinting from #9007), 350ms is spent in `RealFs::load`. This change slashes that figure to ~110ms, which is still *a lot*. About 60ms out of 110ms remaining is spent zeroing memory. Sadly, `AsyncReadExt` API forces us to zero a buffer we're reading into (whether it's via read_to_string or read_exact), but at the very least this commit alleviates unnecessary reallocations. We could probably use something like [simdutf8](https://docs.rs/simdutf8/latest/simdutf8/) to speed up UTF8 validation in this method as well, though that takes only about ~18ms out of 110ms, so while it is significant, I've left that out for now. Memory zeroing is a bigger problem at this point. Before:  After:  /cc @as-cii Release Notes: - Improved performance when loading large files. |
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