> we compile the binary with debug symbols and a flag to compress the debug symbols sections to avoid having huge binary.
How big are the uncompressed debug symbols? I'd expected processing uncompressed debug symbols to happen via a memory mapped file, while compressed debug symbols probably need to be extracted to anonymous memory.
The compressed symbols sounds like the likely culprit. Do you really need a small executable? The uncompressed symbols need to be loaded into RAM anyway, and if it is delayed until it is needed then you will have to allocate memory to uncompress them.
For this particular service, the size does not matter really. For others, it makes more diff (several hundred of Mb) and as we deploy on customers infra, we want images' size to stay reasonable.
For now, we apply the same build rules for all our services to stay consistent.
Maybe I'm not communicating well. Or maybe I don't understand how the debug symbol compression works at runtime. But my point is that I don't think you are getting the tradeoff you think you are getting. The smaller executable may end up using more RAM. Usually at the deployment stage, that's what matters.
Smaller executables are more for things like reducing distribution sizes, or reducing process launch latency when disk throughput is the issue. When you invoke compression, you are explicitly trading off runtime performance in order to get the benefit of smaller on-disk or network transmission size. For a hosted service, that's usually not a good tradeoff.
It is most likely me reading too quickly. I was caught off guard by the article gaining traction in a Sunday, and as I have other duties during the weekend, I am reading/responding only when I can sneak in.
For your comment, I think you are right regarding compression of debug symbols that add up to the peak memory, but I think you are misleading when you think the debug symbols are uncompressed when the app/binary is started/loaded. Decompression only happens for me when this section is accessed by debugger or equivalent.
It is not the same thing as when the binary is fully compressed, like with upx for example.
I have done a quick sanity check on my desktop, I got.
From rss memory at startup I get ~128 MB, and after the panic at peak I get ~474 MB.
So the peak is taller indeed when the debug section is compressed, but the binary in memory when started is roughly equivalent. (virtual mem too)
I had some hard time getting a source that may validate my belief regarding when the debug symbol are uncompressed. But based on https://inbox.sourceware.org/binutils/20080622061003.D279F3F... and the help of claude.ai, I would say it is only when those sections are accessed.
for what is worth, the whole answer of claude.ai
The debug sections compressed with --compress-debug-sections=zlib are decompressed:
At runtime by the debugger (like GDB) when it needs to access the debug information:
When setting breakpoints
When doing backtraces
When inspecting variables
During symbol resolution
When tools need to read debug info:
During coredump analysis
When using tools like addr2line
During source-level debugging
When using readelf with the -w option
The compression is transparent to these tools - they automatically handle the decompression when needed. The sections remain compressed on disk, and are only decompressed in memory when required.
This helps reduce the binary size on disk while still maintaining full debugging capabilities, with only a small runtime performance cost when the debug info needs to be accessed.
The decompression is handled by the libelf/DWARF libraries that these tools use to parse the ELF files.
How big are the uncompressed debug symbols? I'd expected processing uncompressed debug symbols to happen via a memory mapped file, while compressed debug symbols probably need to be extracted to anonymous memory.
https://github.com/llvm/llvm-project/issues/63290