On Fri, Apr 30, 2021 at 8:09 PM Michael <confabul...@kintzios.com> wrote:
> On Friday, 30 April 2021 02:30:51 BST Adam Carter wrote: > > On Wed, Apr 28, 2021 at 7:58 PM Kai Peter <k...@lists.qware.org> wrote: > > > Hi, > > > > > > I have an issue with a machine where I'm not able to detect the real > > > root cause. It hangs up totally. It seems like it was running out of > > > memory - but why? Hopefully somebody can give me some insight. As far I > > > can see right now, it hangs up a few hours after an `emerge --update > > > --newuse --deep --with-bdeps=y @world`. > > > > > > The machine is an Intel Atom with 8 GB RAM (physical, max) and 24 GB > > > swap (a file). So 32 GB RAM in total. > > > > Might be worth adding zswap using zstd or lz4 to your config (uses more > CPU > > for less IO) > > https://www.kernel.org/doc/html/latest/vm/zswap.html > > Zswap will help optimise the swapping of cold pages out of RAM into the > compressed zswap cache and eventually push these out to the disk. This > won't > help with the problem of not having enough RAM to start with for compiling > packages with large resource requirements, like e.g. Chromium. > Yep, but the system is already at its full RAM, so we're in workaround/tactical solution territory. Any system that needs 24gig swap to support 8gig ram is going to really suck. > > With monster packages where more RAM is needed even for a single > compilation > job, after all cold pages have been swapped out, hot pages will start > being > swapped out/in. I think at this point the same I/O race condition will > ensue > as if no zswap were available, plus a compress/decompress CPU load. I > guess > the point of starting to thrash the on-disk swap trying to free RAM may > start > sooner, since RAM which would otherwise be available for the single > prioritised compilation job is now being used by zswap. So, there would > be a > sweet spot in using zswap to improve I/O performance, but it could end up > becoming a disbenefit on compilation of RAM hungry packages. > > Please correct my reasoning above if I have misunderstood how zswap works. > What you've said sounds reasonable to me.
