Date: Thu, 29 Mar 2012 09:14:52 -0700 From: David Wolfskill <david@catwhisker.org> To: "O. Hartmann" <ohartman@mail.zedat.fu-berlin.de> Cc: Current FreeBSD <freebsd-current@freebsd.org> Subject: Re: Using TMPFS for /tmp and /var/run? Message-ID: <20120329161452.GZ1709@albert.catwhisker.org> In-Reply-To: <4F746F1E.6090702@mail.zedat.fu-berlin.de> References: <4F746F1E.6090702@mail.zedat.fu-berlin.de>
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On Thu, Mar 29, 2012 at 04:18:06PM +0200, O. Hartmann wrote:
> I was wondering if there are some objections using TMPFS for /tmp and
> /var/run.
> ...
> My question is whether there are objections using TMPFS for bot /tmp/
> and /var/run/ at this stage on FreeBSD 10.0-CURRENT/amd64?
> ....
I have no experience using tmpfs for /var/run, but I have been using it
for /tmp for some time (mostly in i386, though).
While I use it quite successfully on machines with a small number of
folks actively busy -- e.g., my desktop; my laptop; my home machines), I
encountered some issues when I tried to do so on machines that were
intended for significantly "heavier" use. Specifically:
* Compared to an md-resident /tmp, a tmpfs-resident /tmp has much less
flexibility for specifying the size. Per mdconfig(8), the former
uses:
-s size
Size of the memory disk. Size is the number of 512 byte sectors
unless suffixed with a b, k, m, g, or t which denotes byte, kilo-
byte, megabyte, gigabyte and terabyte respectively. Options -a
and -t swap are implied if not specified.
while the latter uses:
size Specifies the total file system size in bytes. If zero (the
default) or a value larger than SIZE_MAX - PAGE_SIZE is given,
the available amount of memory (including main memory and swap
space) will be used.
In this configuration, I would have preferred to have specified
about 10GB for /tmp. I wouldn't mind if it spilled to swap space,
but I certaianly didn't want it using 10GB of RAM -- especially since
the machines only had 6GB RAM.
Nor did I especially want *all* of the swap space used for /tmp. I
would have allocated (say) 20GB for swap. I wouldn't mind if half of
that were used for /tmp -- but a reason I allocate so much swap is
that I've seen what happens when a machine runs out of swap, and it
wasn't pretty.
In any case, effective maximum usable size for tmpfs involves SIZE_MAX
(~4G) & PAGE_SIZE (4K, in my case).
* Even when I went ahead and created a tmpfs for /tmp, I'd get ENOSPC
whenever I tried to allocate anything on it -- until I dropped the
size specification to <2G (2**32). Well, 2GB for /tmp just wasn't at
all likely to be useful for my purposes in this case.
So I continue to use tmpfs for /tmp for machines with fewer folks
logging in, but I'm a bit less enthusiastic about its use unless the
workload and other requirements are fairly carefully considered
beforehand.
Peace,
david
--
David H. Wolfskill david@catwhisker.org
Depriving a girl or boy of an opportunity for education is evil.
See http://www.catwhisker.org/~david/publickey.gpg for my public key.
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