On Wed, Sep 4, 2019 at 12:01 PM Kyle Marek <psppsn96@xxxxxxxxx> wrote: > > I'm finding that 32G is not necessarily sufficient for compiling clang > itself. Similarly I've had a hard time compiling UnrealEngine from > source. I usually see ld using up to 12G of memory to link each > artifact. Using -j$(nproc) on a 16 VCPU system amplifies the issue. I > rely on adding another 32G swap file to complete the job. I setup swap on ZRAM device at 1.5X RAM. That was just as intermittently unresponsive (seconds, and periods above 10 minutes) GUI, to the degree using the laptop as a laptop was pointless. But, webkitgtk build did complete with the default command, and in a shorter time than with a swap partition on SSD (which became sufficiently unresponsive even via ssh that I gave up and forced power off). But, I don't think I can recommend such a setup as a default installation of Fedora Workstation. On a system with 32G RAM, that would mean a 48G /dev/zram device for swap. If it completely filled up, it would use ~24G of RAM, leaving 8GiB for compiling + OS + workstation stuff. You are getting a huge swap device that's almost as fast as RAM, but it's so fast that it means burning a huge amount of CPU cycles on compression/decompression. And kswapd is not threaded, it maxes out at 100% of a single core, and once it's there, that's it, you can't scale beyond it. > I'm now using an NVME SSD for my swap file. No more hangs for the most > part! Usually if I lock up, it's for maybe a minute before OOM steps in. > > However, I'd definitely like to see a non-zram "solution" for use cases > like this. Ultimately I'd like to see the use of traditional swap files > to not hang a system even if it is placed on a md RAID array. I'm > guessing that the long term fix is for OOM to happen sooner, and/or > kernel schedulers to be improved, as mentioned elsewhere in this thread. > Ideally this wouldn't require the use of systemd or cgroups to make it > possible. I'm skeptical of swapfiles for this use case, because it likely increases the chance for file system disk contention, see section 11.17 https://www.kernel.org/doc/gorman/html/understand/understand014.html And in heavy swap use and memory pressure, I already see evidence of applications evicting their own executable code and constantly re-reading it from disk. That's increasing the chance of IO pressure resulting in stalls. Incidental swap is fine, and I think it's possible to use either zram or zswap to moderate the transition to a swap partition. But once this grows to an aggressive swap dependency, the desktop is responsiveness is lost. -- Chris Murphy _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
