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by sghemawat 4858 days ago
About [1] Sorry about that: the document you linked to is amazingly stale. tcmalloc has been releasing memory to the system for many years. See for example the IncrementalScavenge routine in a version of page_heap.cc from Dec 2008:

https://code.google.com/p/gperftools/source/browse/trunk/src...

One caveat: physical memory and swap space is released, but the process's virtual size will not decrease since tcmalloc uses madvise(MNONE) to release memory.

About [2], code using tcmalloc-specific features/symbols is definitely a problem. I would strongly advise against doing that and sticking to the libc interfaces instead for the reason you pointed out.
2 comments
jeffdavis 4858 days ago
Strange, the page showed up first when I googled "tcmalloc" and the problem was also present in the version that I was using (at least I think it was). My apologies.

Yeah, regarding [2], that was definitely not my idea.

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sghemawat 4858 days ago
Not your fault. We just plain forgot to update the documentation, so the freshest available document is a few years out of date.
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jeffffff 4858 days ago
wow i didn't realize madvise could actually modify the memory contents and return pages, but it makes sense that it can because that is a useful feature. very cool!
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