This is respin of: https://lwn.net/ml/linux-kernel/20190110220718.261134-1-surenb@xxxxxxxxxx/ Android is adopting psi to detect and remedy memory pressure that results in stuttering and decreased responsiveness on mobile devices. Psi gives us the stall information, but because we're dealing with latencies in the millisecond range, periodically reading the pressure files to detect stalls in a timely fashion is not feasible. Psi also doesn't aggregate its averages at a high-enough frequency right now. This patch series extends the psi interface such that users can configure sensitive latency thresholds and use poll() and friends to be notified when these are breached. As high-frequency aggregation is costly, it implements an aggregation method that is optimized for fast, short-interval averaging, and makes the aggregation frequency adaptive, such that high-frequency updates only happen while monitored stall events are actively occurring. With these patches applied, Android can monitor for, and ward off, mounting memory shortages before they cause problems for the user. For example, using memory stall monitors in userspace low memory killer daemon (lmkd) we can detect mounting pressure and kill less important processes before device becomes visibly sluggish. In our memory stress testing psi memory monitors produce roughly 10x less false positives compared to vmpressure signals. Having ability to specify multiple triggers for the same psi metric allows other parts of Android framework to monitor memory state of the device and act accordingly. The new interface is straight-forward. The user opens one of the pressure files for writing and writes a trigger description into the file descriptor that defines the stall state - some or full, and the maximum stall time over a given window of time. E.g.: /* Signal when stall time exceeds 100ms of a 1s window */ char trigger[] = "full 100000 1000000" fd = open("/proc/pressure/memory") write(fd, trigger, sizeof(trigger)) while (poll() >= 0) { ... }; close(fd); When the monitored stall state is entered, psi adapts its aggregation frequency according to what the configured time window requires in order to emit event signals in a timely fashion. Once the stalling subsides, aggregation reverts back to normal. The trigger is associated with the open file descriptor. To stop monitoring, the user only needs to close the file descriptor and the trigger is discarded. Patches 1-4 prepare the psi code for polling support. Patch 5 implements the adaptive polling logic, the pressure growth detection optimized for short intervals, and hooks up write() and poll() on the pressure files. The patches were developed in collaboration with Johannes Weiner. The patches are based on 4.20-rc7. Johannes Weiner (2): fs: kernfs: add poll file operation kernel: cgroup: add poll file operation Suren Baghdasaryan (3): psi: introduce state_mask to represent stalled psi states psi: rename psi fields in preparation for psi trigger addition psi: introduce psi monitor Documentation/accounting/psi.txt | 104 ++++++ fs/kernfs/file.c | 31 +- include/linux/cgroup-defs.h | 4 + include/linux/kernfs.h | 6 + include/linux/psi.h | 10 + include/linux/psi_types.h | 83 ++++- kernel/cgroup/cgroup.c | 119 +++++- kernel/sched/psi.c | 605 ++++++++++++++++++++++++++++--- 8 files changed, 891 insertions(+), 71 deletions(-) Changes in v3: - Added smp_mb in the slowpath, as per Peter - Changed psi_group.polling flag to atomic_t, as per Peter - Added a comment in the hotpath about implicit smp_wmb in the chmxchg, as per Johannes - Minimized line-breaks wherever possible, as per Peter -- 2.20.1.321.g9e740568ce-goog
