On Mon 27-02-23 17:08:30, Mike Rapoport wrote: [...] > The results you present do show improvement in IPC for an artificial test > script. But more interesting would be to see how a real world workloads > benefit from your changes. It's been quite some time ago (2018ish) when we have seen bug report where mount got stalled when racing with memory reclaim. This was nasty because the said mount was a part of login chain and users simply had to wait for a long time to get loged in in that particular deployment. The mount was blocked on a shrinker registration and the reclaim was stalled in a slab shrinker IIRC. I do not remember all the details but the underlying problem was that a shrinker callback took a long time because there were too many objects to scan or it had to sync with other fs operation. I believe we ended up using Minchan's break out from slab shrinking if the shrinker semaphore was contended and that helped to some degree but there were still some corner cases where a single slab shrinker could take a noticeable amount of time. In general using a "big" lock like shrinker_rwsem from the reclaim and potentially block many unrelated subsystems that just want to register or unregister shrinkers is a potential source of hard to predict problems. So this is a very welcome change. -- Michal Hocko SUSE Labs
