| # Fine-grained collection of memory stats |
| |
| The Chromium OS memory daemon (`memd`) is a lightweight collector of values and |
| events related to system memory. |
| |
| `Memd` runs continuously, but is mostly asleep when memory pressure is low. As |
| pressure increases, it starts sampling rapidly various kernel-supplied |
| quantities, mainly from `/proc/vmstat`. It also collects events, such as the |
| crossing of the _available memory_ threshold which produces a low-memory |
| notification. |
| |
| The sampling and event collection is done in an in-memory circular buffer. |
| Certain "interesting" events trigger a _collection_, that is make `memd` dump a |
| range of samples and events around the interesting events into a _clip file_ in |
| `/var/log/memd`. Clip files are also rotated, and the older ones get |
| eventually clobbered by new events. |
| |
| The intent is that `memd` output be collected alongside the rest of the |
| logs collected with feedback reports. If the report was motivated by poor |
| behavior of the memory subsystem, the data will be directly useful. Otherwise |
| the data can be opportunistically used for analysis. |
