Hi folks, These patches introduce non-blocking inodegc pushes to fix long hold-offs in statfs() operations when inodegc is performing long running inode inactivation operations. The first patch introduces the bound maximum work start time for the inodegc queues - it's short, only 1 jiffie (10ms) - but we don't want to delay inodegc for an arbitrarily long period of time. However, it means that work always starts quickly and so that reduces the need for statfs() to have to wait for background inodegc to start and complete to catch space "freed" by recent unlinks. The second patch converts statfs to use a "push" rather than a "flush". The push simply schedules any pending work that hasn't yet timed out to run immediately and returns. It does not wait for the inodegc work to complete - that's what a flush does, and that's what caused all the problems for statfs(). Hence statfs() is converted to push semantics at the same time, thereby removing the blocking behaviour it currently has. This should prevent a large amount of the issues that have been seeing with lots of processes stuck in statfs() - that will no long happen. The only time user processes should get stuck now is when the inodegc throttle kicks in (unlinks only at this point) or if we are waiting for a lock a long running inodegc operation holds to be released. We had those specific problems before background inodegc - they manifested as unkillable unlink operations that had every backed up on them instead of background inodegc that has everything backed up on them. This patch has been running in my test environment for nearly a month now without regressions occurring. While there are likely still going to be inodegc flush related hold-offs in certain circumstances, nothing appears to be impacting the correctness of fstests tests or creating new issues. The 0-day kernel testing bot also indicates that certain benchmarks (such as aim7 and stress-ng.rename) run significantly faster with bound maximum delays and non-blocking statfs operations. Comments, thoughts and testing appreciated. -Dave. Version 2: - Also convert quota reportting inodegc flushes to a push.
