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List:       opensolaris-ufs-discuss
Subject:    [ufs-discuss] tmpfs should have mount option to reserve space
From:       "Richard L. Hamilton" <rlhamil () smart ! net>
Date:       2010-07-18 19:01:58
Message-ID: 782332398.51279504950510.JavaMail.Twebapp () sf-app1
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tmpfs draws space from virtual memory (RAM+swap), and
is typically used for
/tmp
/etc/svc/volatile
/var/run

The latter two are for system use, and have restricted
permissions.  /tmp is wide open, for any application to use.

Because tmpfs uses virtual memory, the amount of space available
may vary without regard to how much it uses.  An upper limit
can be placed on a tmpfs mount with the "size" mount option.
That can prevent excessive use of especially /tmp from consuming
excessive VM.

But there is presently no way to guarantee a minimum amount of
space for any given tmpfs mount.  For /tmp, running out of space
will more often than not only affect applications.  But if
/etc/svc/volatile runs out of space, that might affect the
proper operation of SMF.

/etc/svc/volatile and /var/run typically consume relatively
limited amounts of space; say, 2MB each or less.

I think it might be useful to have a mount option to reserve
a certain amount of space for a particular tmpfs mount.
That would be in addition to the "size" option that sets
a maximum.  If both were used, "size" should have to be
greater than or equal to the reserved minimum; if "size"
was larger, space up to the minimum would be guaranteed,
and up to "size" would be permitted if available.

What do you all think?
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