Re: [gentoo-user] Re: /var/tmp/portage on tmpfs

[Rich Freeman]

On Wed, Jan 7, 2015 at 12:26 PM, Neil Bothwick <neil@××××××××××.uk> wrote:
> On Wed, 7 Jan 2015 16:12:28 +0000 (UTC), James wrote:
>
>> > That's why I thought XFS may help.
>> > Reports of the speed gain from tmpfs are quite mixed, but I do use it
>> > myself.
>>
>> I'm moving to btrfs and eventually ceph, so xfs is not on my roadmap....
>
> Not as a general FS, but as a specific choice for $PORTAGE_TMPDIR it may
> be worth testing. XFS was designed for an environment that used temporary
> files that didn't need to be committed to disk, so its caching doesn't
> write to disk anywhere near as often. That means you would be working
> with files stored in RAM a lot of the time.
>

If you're going to be saving the build files using mv/ln (or with cp
--reflink on a filesystem that supports this), then the LAST thing I
would do is use a different fs for PORTAGE_TMPDIR.  The
best-performing option would be to make it a directory on the same
filesystem as wherever you're going to store the files by
moving/(ref)linking them.  That makes the move/(ref)link operation
require minimal IO.

If you put PORTAGE_TMPDIR on xfs, and then mv all those files to a
separate filesystem, then you're going to have to do a disk-to-disk
copy of everything and a removal of the original files.  That is
expensive in terms of IO.  At last with a tmpfs you're just doing
memory-to-disk so you're only doing disk IO once.

If you're going to create tarballs then tmpfs will still be fastest,
but using another filesystem for PORTAGE_TMPDIR isn't a problem since
you're going to have to do disk-to-disk IO no matter what, since
creating a tarball will always require rewriting everything.

-- 
Rich