| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Aleksey Demakov <ademakov(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Experimental dynamic memory allocation of postgresql shared memory |
| Date: | 2016-06-17 18:31:53 |
| Message-ID: | 20160617183153.5n6petzuv6m4lxw2@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
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.
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