Usage of /tmp on Solaris buildfarm

[Dagobert Michelsen]

Hi Jörg,

Am 21.06.2019 um 12:34 schrieb Joerg Schilling <Joerg.Schilling at fokus.fraunhofer.de>:
> Dagobert Michelsen via buildfarm <buildfarm at lists.opencsw.org> wrote:
>> we noticed that you store a lot of stuff in /tmp. This is discouraged in Solaris as /tmp
>> is a memory filesystem - files there directly occupy RAM which is then missing from
>> file system cache making the whole system unusable slow. Please do not store stuff there,
>> if you need more space I can increase your quota. Your regular home is on ZFS with lazy write
>> enabled, so writing to /tmp should also not be faster than writing to your home directory.
> 
> These files do not occupy RAM but rather virtual memory.
> 
> So they do not really affect the system performance.

Ah, a memory discussion I have been missing out for a long time! :-)
Indeed /tmp is taken from virtual memory if there is no further configuration,
which is SWAP + RAM. When you fill up /tmp with more stuff than SWAP you do take away
RAM. Additionally, you get paging activity in terms of pageout if RAM gets low
(or increased scanner frequency if you go below „lotsfree“ which is slower than
the ZFS delayed writes (remember I have enabled delayed writes and disabled ZIL on
this box and lofs does not change semantics). Please also note that this is a rather
old Solaris 10 kernel and especially the memory system change considerably during Solaris 11
development. If you have further insights I am all ears :-)


Best regards

  — Dago

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