[Lldb-commits] [PATCH] D68549: make ConstString allocate memory in non-tiny chunks

Tue Oct 8 12:22:04 PDT 2019

llunak added a comment.

In D68549#1700019 <https://reviews.llvm.org/D68549#1700019>, @aprantl wrote:

> This makes sense to me. We may need to make this configurable for low-memory hosts at some point.

Note that the memory usage shouldn't be as bad as it might look. As long as the BumpPtrAllocatorImpl size exceeds the threshold for a separate allocation (glibc malloc will use separate mmap for anything >=128KiB), memory for the virtual memory will be really allocated only if needed. And even if, that 1MiB is nowhere near the 15MiB liblldb.so takes here.

In D68549#1700022 <https://reviews.llvm.org/D68549#1700022>, @aprantl wrote:

> I assume you experimented with many different values, and these are the best tradeoff?

I've tried few and picked what seemed reasonable. 64KiB for the allocator didn't perform as well, but then I don't think there's one good number, so I didn't really try to look for one. Also I tried just with my one specific use case, and this cannot be benchmarked precisely. The logic was basically just that for small projects this doesn't really matter because they won't take up much memory anyway and for those that do this should perform better.

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https://reviews.llvm.org/D68549