tcmalloc

You are talking about the old tcmalloc from 2006 that should never be used anymore. There is also a new tcmaloc: https://github.com/google/tcmalloc/ If you are in doubt, you should simply use what ClickHouse is using.

This is factually false, and I'm wondering why you'd say that. Some of the more common malloc implementations out there are dlmalloc, jemalloc, and tcmalloc. Here is where they call munmap. https://github.com/ennorehling/dlmalloc/blob/71296436f979a35... https://github.com/jemalloc/jemalloc/blob/c0c9783ec9289e6d1d... Note that not all allocators work this way, you can see that tcmalloc will instead MADV_DONTNEED. (You can find munmap in tcmalloc, but it's not being used to free memory.) https://github.com/google/tcmalloc/blob/48808681a9f38e974b49...

Not true. mmap is commonly used in malloc implementations. Look at this man page for jemalloc. http://jemalloc.net/jemalloc.3.html "Traditionally, allocators have used sbrk(2) to obtain memory, which is suboptimal for several reasons, including race conditions, increased fragmentation, and artificial limitations on maximum usable memory. If sbrk(2) is supported by the operating system, this allocator uses both mmap(2) and sbrk(2), in that order of preference; otherwise only mmap(2) is used." Also, Google's tcmalloc uses mmap to get system memory: https://github.com/google/tcmalloc/blob/master/docs/design.m... "An allocation for k pages is satisfied by looking in the kth free list. If that free list is empty, we look in the next free list, and so forth. Eventually, we look in the last free list if necessary. If that fails, we fetch memory