Monitoring

Authors: Kunwu Chan <kunwu.chan@gmail.com>, Wang Lian <lianux.mm@gmail.com> Overview DAMON monitors data access by sampling PTE (Page Table Entry) Accessed bits. It clears the Accessed bit but does not flush the TLB (Translation Lookaside Buffer). This is an intentional design choice. Questions about this behavior come up repeatedly, both on the mailing list and in private inquiries. This document describes the reasoning, the trade-offs, and recommendations for users and testers. Background DAMON’s access check works as follows:...

The initial version of this post was initially posted to DAMON mailing list as https://lore.kernel.org/20241108232536.73843-1-sj@kernel.org Posting it here too, for visibility and after-posting updates for any needs. One of common issues that I received from DAMON users is that DAMON’s monitoring results show hot regions much less than expected. Specifically, the users find regions of only zero or low ’nr_accesses’ value from the DAMON-generated access pattern snapshots. In some cases, it turned out the problem can be alleviated by tuning DAMON parameters or changing the way to interpret the results....