| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ========================== |
| Frequently Asked Questions |
| ========================== |
| |
| Why a new subsystem, instead of extending perf or other user space tools? |
| ========================================================================= |
| |
| First, because it needs to be lightweight as much as possible so that it can be |
| used online, any unnecessary overhead such as kernel - user space context |
| switching cost should be avoided. Second, DAMON aims to be used by other |
| programs including the kernel. Therefore, having a dependency on specific |
| tools like perf is not desirable. These are the two biggest reasons why DAMON |
| is implemented in the kernel space. |
| |
| |
| Can 'idle pages tracking' or 'perf mem' substitute DAMON? |
| ========================================================= |
| |
| Idle page tracking is a low level primitive for access check of the physical |
| address space. 'perf mem' is similar, though it can use sampling to minimize |
| the overhead. On the other hand, DAMON is a higher-level framework for the |
| monitoring of various address spaces. It is focused on memory management |
| optimization and provides sophisticated accuracy/overhead handling mechanisms. |
| Therefore, 'idle pages tracking' and 'perf mem' could provide a subset of |
| DAMON's output, but cannot substitute DAMON. |
| |
| |
| Does DAMON support virtual memory only? |
| ======================================= |
| |
| No. The core of the DAMON is address space independent. The address space |
| specific low level primitive parts including monitoring target regions |
| constructions and actual access checks can be implemented and configured on the |
| DAMON core by the users. In this way, DAMON users can monitor any address |
| space with any access check technique. |
| |
| Nonetheless, DAMON provides vma tracking and PTE Accessed bit check based |
| implementations of the address space dependent functions for the virtual memory |
| by default, for a reference and convenient use. In near future, we will |
| provide those for physical memory address space. |
| |
| |
| Can I simply monitor page granularity? |
| ====================================== |
| |
| Yes. You can do so by setting the ``min_nr_regions`` attribute higher than the |
| working set size divided by the page size. Because the monitoring target |
| regions size is forced to be ``>=page size``, the region split will make no |
| effect. |
