Re: create /tmp with ffs vs. tmpfs ?

[<tlaronde%kergis.com@localhost>]

On Mon, Aug 12, 2024 at 07:30:20AM -0400, Greg Troxel wrote:
> Steve Rikli <sr%genyosha.net@localhost> writes:
> 
> > 1) is my understanding correct? I.e. does tmpfs use main memory for
> >    backing, rather than swap or something else?
> 
> It uses virtual memory which can be paged.  So if you have swap space
> configured, it can be bigger than physical memory.  However, things in
> /tmp will compete with other memory usage.
> 
> > 2) can I configure /tmp as ffs rather than tmpfs?
> 
> Absolutely.   tmpfs is relatively new in the history of unix and having
> tmp as a real filesystem is entirely reasonable.
> 
> > Seems like I should be able to (manually?) configure /tmp as ffs during
> > initial sysinst, or leave some unallocated disk space to do it later.
> 
> As Martin said you can leave it on /.  Original unix tradition was to
> have separate / and /usr, which let you boot if / was ok.  And it
> protects / from becoming full from runaway activities in /usr, like
> actual users on a multiusers system.  So you can make a 4GB /tmp
> separately so that when /tmp is full / is still ok.  Or you can just
> have one giant partition and take your chances, with more efficiency.
> 128G isn't that big a disk.
> 
> Definitely add swap, maybe even more then 4G depending on what you want
> to do.   But 4G is probably enough for anything you want to put up with
> waiting for anyway.

Be sure to always reserve some extra partitions (I personnally prefer
them other swap files) for swapping in order to add more if needed.
I was hit some times by "new" programs that make absolutely no
provision for limited memory and put everything in memory, the
original file and the result (example: jpeg2 files).

Spare space is always a must have.

> 
> > My main thoughts were to avoid using RAM for tmpfs and simply configure
> > a larger swap partition, or add a swap file, etc.
> 
> There is a really good question here.  Which is, for some reasonable
> workloads, building programs that use 100M of /tmp and 1.5 GB of /tmp, how
> things go with
> 
>   both system 4 GB swap
> 
>   A) big / with tmp just part of /
> 
>   B) big / with 2GB tmpfs
> 
> I am really not sure what is better.  I suspect tmpfs performance is
> better for the times when /tmp is only 100-200 MB or so.  I am really
> not sure how it would go with larger.
> 
> When building packages, some are ridiculous, e.g. thunderbird, which I
> think needs around 19 GB of $WRKDIR space.  I have code in mk.conf.local
> to flip from /tmp/work to /nfs/ztmp/work-$hostname where the latter is
> over NFS and a zfs filesystem on a big disk.  It's slow but the builds
> finish.  So you may be able to use a smallish tmpfs and point specific
> big jobs elsewhere.  That's more work but higher performance - after you
> get it right.

-- 
        Thierry Laronde <tlaronde +AT+ kergis +dot+ com>
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