Am Wed, 24 May 2017 11:34:20 -0700 schrieb Ian Zimmerman <i...@primate.net>:
> On 2017-05-24 08:00, Kai Krakow wrote: > > > While I have no benchmarks and use the systemd default of tmpfs for > > /tmp, I also put /var/tmp/portage on tmpfs, automounted through > > systemd so it is cleaned up when no longer used (by unmounting). > > > > What can I say? It works so much faster: Building packages is a lot > > faster most of the time, even if you'd expect gcc uses a lot of > > memory. > > > > Well, why might that be? First, tmpfs is backed by swap space, that > > means, you need a swap partition of course. Swap is a lot simpler > > than file systems, so swapping out unused temporary files is fast > > and is a good thing. Also, unused memory sitting around may be > > swapped out early. Why would you want inactive memory resident? So > > this is also a good thing. Portage can use memory much more > > efficient by this. > > > > Applying this reasoning over to /tmp should no explain why it works > > so well and why you may want it. > > > > BTW: I also use zswap, so tmpfs sits in front of a compressed > > write-back cache before being written out to swap compressed. This > > should generally be much more efficient (performance-wise) than > > putting /tmp on zram. > > > > I configured tmpfs for portage to use up to 30GB of space, which is > > almost twice the RAM I have. And it works because tmpfs is not > > required to be resident all the time: Inactive parts will be swapped > > out. The kernel handles this much similar to the page cache, with > > the difference that your files aren't backed by your normal file > > system but by swap. And swap has a lot lower IO overhead. > > > > Overall, having less IO overhead (and less head movement for portage > > builds) is a very very efficient thing to do. GCC constantly needs > > all sorts of files from your installation (libs for linking, header > > files, etc), and writes a lot of transient files which are needed > > once later and then discarded. There's no point in putting it on a > > non-transient file system. > > > > I use the following measures to get more performance out of this > > setup: > > > > * I have three swap partitions spread across three HDDs > > * I have a lot of swap space (60 GB) to have space for tmpfs > > * I have bcache in front of my HDD filesystem > > * I have a relatively big SSD dedicated to bcache > > > > My best recommendation is to separate swap and filesystem devices. > > While I didn't do it that way, I still separate them through bcache > > and thus decouple fs access and swap access although they are on the > > same physical devices. My bcache is big enough that most accesses > > would go to the SSD only. I enabled write-back to have that effect > > also for write access. > > > > If you cannot physically split swap from fs, a tmpfs setup for > > portage may not be recommended (except you have a lot of memory, > > like 16GB or above). But YMMV. > > > > Still, I recommend it for /tmp, especially if your system is on > > SSD. > > All interesting points, and you convinced me to at least give tmpfs a > try on the desktop. > > My laptop is different, though. It doesn't have that much RAM by > comparison (4G) and it _only_ has a SSD. Builds have been slow :( I > am afraid to mess with it lest I increase the wear on the SSD. You still may want to test /var/tmp/portage as tmpfs for small packages... Or manually call: # sudo PORTAGE_TMPDIR=/path/to/tmpfs emerge -1a small-package For big packages, I suggest to nfs mount some storage from your desktop. It probably will still be slow (maybe a little bit slower) but should be much better for your SSD lifetime. > > Unix semantics suggest that /tmp is not expected to survive reboots > > anyways (in contrast, /var/tmp is expected to survive reboots), so > > tmpfs is a logical consequence to use for /tmp. > > /tmp is wiped by the bootmisc init job anyway. That's why such jobs exist, and why usually /tmp is wiped completely while /var/tmp is wiped based on atime/mtime... -- Regards, Kai Replies to list-only preferred.
