/tmp: change default to mdmfs and/or tmpfs?

[Dmitry Morozovsky]

On Sun, 9 Jun 2013, Jeremy Chadwick wrote:

[back to second part]

[and snip a lot here too]

> Where someone stated that excessive ARC usage on ZFS had an indirect
> effect on tmpfs.  r233769 to stable/9 may have fixed this, but given the
> history of all of this "juggling" of Feature X causing memory exhaustion
> for Feature Y, and in turn affecting Feature Z, all within kernel space,
> I really don't know how much I can trust all of this.
> 
> One should probably review the FreeBSD forums for other posts as well,
> as gut feeling says there's probably more there too.

.. that's why I'm trying to discuss this in public (maybe wrong list had been 
chosen, perhaps -stable@ would fit a bit more) -- to share knowledge, opinions 
and other related stuff ;)

> In closing:
> 
> If you want to make bsdinstall ask/prompt the administrator "would you
> like to use tmpfs for /tmp?", then I'm all for it -- sounds good to me.
> But doing it by default would be something (at this time) I would not be
> in favour of.  I just don't get the impression of stability from tmpfs
> given its track record.  (Yes, I am paranoid in this regard)

Agree at most.

> *** -- For example I personally have experienced strange behaviour when
> ZFS+UFS are used on the same system with massive amounts of I/O being
> done between the two (my experience showed the ZFS ARC suddenly limiting
> itself in a strange manner, to some abysmally small limit (much lower
> than arc_max)).  In this case, I can only imagine tmpfs making things
> "even worse" given added memory pressure and so on.

For our backup server, which uses rather huge 24*2T raidz2 and periodically 
synced on eSATA UFS, I sometimes seen speed drops, but nothing really bad.
It's stable/9 with 16G of RAM though, perhaps on systems where RAM is tighter 
the situation could be much worse...


-- 
Sincerely,
D.Marck                                     [DM5020, MCK-RIPE, DM3-RIPN]
[ FreeBSD committer:                                 marck at FreeBSD.org ]
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*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at rinet.ru ***
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