Re: Experimental dynamic memory allocation of postgresql shared memory

On 2016-06-18 00:23:14 +0600, Aleksey Demakov wrote:
> Finally, it's possible to repeatedly mmap
> and munmap on portions of a contiguous address space providing
> a given addr argument for both of them. The last option might, of
> course, is susceptible to hijacking this portion of the address by an
> inadvertent caller of mmap with NULL addr argument. But probably
> this could be avoided by imposing a disciplined use of mmap in
> postgresql core and extensions.

I don't think that's particularly realistic. malloc() uses mmap(NULL)
internally.  And you can't portably mmap non-file backed memory from
different processes; you need something like tmpfs backed / posix shared
memory / for it.  On linux you can do stuff like madvise(MADV_FREE),
which kinda helps.