On Fri, Mar 08, 2019 at 10:43:04AM -0800, Suren Baghdasaryan wrote: > This is respin of: > https://lwn.net/ml/linux-kernel/20190206023446.177362-1-surenb%40google.com/ > > 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 1-6 prepare the psi code for polling support. Patch 7 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 5.0-rc8 (Merge tag 'drm-next-2019-03-06'). > > Suren Baghdasaryan (7): > psi: introduce state_mask to represent stalled psi states > psi: make psi_enable static > psi: rename psi fields in preparation for psi trigger addition > psi: split update_stats into parts > psi: track changed states > refactor header includes to allow kthread.h inclusion in psi_types.h > psi: introduce psi monitor > > Documentation/accounting/psi.txt | 107 ++++++ > include/linux/kthread.h | 3 +- > include/linux/psi.h | 8 + > include/linux/psi_types.h | 105 +++++- > include/linux/sched.h | 1 - > kernel/cgroup/cgroup.c | 71 +++- > kernel/kthread.c | 1 + > kernel/sched/psi.c | 613 ++++++++++++++++++++++++++++--- > 8 files changed, 833 insertions(+), 76 deletions(-) > > Changes in v5: > - Fixed sparse: error: incompatible types in comparison expression, as per > Andrew > - Changed psi_enable to static, as per Andrew > - Refactored headers to be able to include kthread.h into psi_types.h > without creating a circular inclusion, as per Johannes > - Split psi monitor from aggregator, used RT worker for psi monitoring to > prevent it being starved by other RT threads and memory pressure events > being delayed or lost, as per Minchan and Android Performance Team > - Fixed blockable memory allocation under rcu_read_lock inside > psi_trigger_poll by using refcounting, as per Eva Huang and Minchan > - Misc cleanup and improvements, as per Johannes > > Notes: > 0001-psi-introduce-state_mask-to-represent-stalled-psi-st.patch is unchanged > from the previous version and provided for completeness. Please fix kbuild test bot's warning in 6/7 Other than that, for all patches, Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
