On Mon 16-07-18 10:57:45, Daniel Drake wrote: > Hi Johannes, > > Thanks for your work on psi! > > We have also been investigating the "thrashing problem" on our Endless > desktop OS. We have seen that systems can easily get into a state where the > UI becomes unresponsive to input, and the mouse cursor becomes extremely > slow or stuck when the system is running out of memory. We are working with > a full GNOME desktop environment on systems with only 2GB RAM, and > sometimes no real swap (although zram-swap helps mitigate the problem to > some extent). > > My analysis so far indicates that when the system is low on memory and hits > this condition, the system is spending much of the time under > __alloc_pages_direct_reclaim. "perf trace -F" shows many many page faults > in executable code while this is going on. I believe the kernel is > swapping out executable code in order to satisfy memory allocation > requests, but then that swapped-out code is needed a moment later so it > gets swapped in again via the page fault handler, and all this activity > severely starves the system from being able to respond to user input. > > I appreciate the kernel's attempt to keep processes alive, but in the > desktop case we see that the system rarely recovers from this situation, > so you have to hard shutdown. In this case we view it as desirable that > the OOM killer would step in (it is not doing so because direct reclaim > is not actually failing). Yes this is really unfortunate. One thing that could help would be to consider a trashing level during the reclaim (get_scan_count) to simply forget about LRUs which are constantly refaulting pages back. We already have the infrastructure for that. We just need to plumb it in. -- Michal Hocko SUSE Labs
