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

[gevisz <gevisz@gmail.com>]

2018-02-08 20:13 GMT+02:00 Rich Freeman <rich0@gentoo.org>:
> On 08/02/18 19:11, gevisz wrote:
>>
>> I never used tmpfs for portage TMPDIR before and now decided to give it a
>> try.
>>
>> I have 8GB of RAM and 12GB of swap on a separate partition.
>>
>> Do I correctly understood
>> https://wiki.gentoo.org/wiki/Portage_TMPDIR_on_tmpfs
>> that I can safely set in the fstab the size of my tmpfs to 12GB so
>> that the chromium could be emerged in tmpfs (using the swap)
>>  without the need to set notmpfs.conf for chromium and the likes.
>
> You can try it, but for Chromium these days you might find that still
> doesn't perform great.  I have 16GB of RAM (no swap) and have moved
> back to building on SSD for that one package (with ccache to help).
>
> In an ideal world swap would STILL be better than building on disk,
> because it gives the kernel fewer constraints around what gets written
> to disk.

> Anything written to disk MUST end up on the disk within the dirty
> writeback time limit.  Anything written to tmpfs doesn't ever have to
> end up on disk, and if it is swapped the kernel need not do it in any
> particular timeframe.  Also, the swapfile doesn't need the same kinds
> of integrity features as a filesystem, which probably lowers the cost
> of writes somewhat (if nothing else after a reboot there is no need to
> run tmpreaper on it).

> So, swapping SHOULD still be better than building on disk, because any
> object file that doesn't end up being swapped is a saved disk IO, and
> the stuff that does get swapped will hopefully get written at a more
> opportune time vs forcing the kernel to stop what is doing after 30s
> (by default) to make sure that something gets written no matter what
> (if it wasn't deleted before then).

Thank you for the reply.

I probably try a pure tmpfs + swap solution. If it fails some day, I will
then add notmpfs exceptions.

However, it probably won't be sooner than
# emerge --update --deep --with-bdeps=y --newuse --backtrack=90 --ask
world --exclude chromium
fails because of the "--exclude chromium" part :), as I have already compiled
the recent vertion of chromium with /var/tmp/portage on the hard disk and
it took more than 24 hours on my old AMD Athlon X2 with j2 option. :(