DAMON maintains the targets in a list, and allows committing only an entire list of targets having the new parameters. Targets having same index on the lists are treated as matching source and destination targets. If an existing target cannot find a matching one in the sources list, the target is removed. This means that there is no way to remove only a specific monitoring target in the middle of the current targets list.
Such pin-point target removal is really needed in some use cases, though. Monitoring access patterns on virtual address spaces of processes that spawned from the same ancestor is one example. If a process of the group is terminated, the user may want to remove the matching DAMON target as soon as possible, to save in-kernel memory usage for the unnecessary target data. The user may also want to do that without turning DAMON off or removing unnecessary targets, to keep the current monitoring results for other active processes. Extend DAMON kernel API and sysfs ABI to support the pin-point removal in the following way. For API, add a new damon_target field, namely 'obsolete'. If the field on parameters commit source target is set, it means the matching destination target is obsolete. Then the parameters commit logic removes the destination target from the existing targets list. For sysfs ABI, add a new file under the target directory, namely 'obsolete_target'. It is connected with the 'obsolete' field of the commit source targets, so internally using the new API. Also add a selftest for the new feature. The related helper scripts for manipulating the sysfs interface and dumping in-kernel DAMON status are also extended for this. Note that the selftest part was initially posted as an individual RFC series [1], but now merged into this one. Bijan Tabatabai ([email protected]) has originally reported this issue, and participated in this solution design on a GitHub issue [1] for DAMON user-space tool. Changes from RFC (https://lore.kernel.org/[email protected]) - Wordsmith commit messages - Add Reviewed-by: tags from Bijan - Add a kselftest for the functionality of the new feature (https://lore.kernel.org/[email protected]) [1] https://github.com/damonitor/damo/issues/36 SeongJae Park (9): mm/damon/core: add damon_target->obsolete for pin-point removal mm/damon/sysfs: test commit input against realistic destination mm/damon/sysfs: implement obsolete_target file Docs/admin-guide/mm/damon/usage: document obsolete_target file Docs/ABI/damon: document obsolete_target sysfs file selftests/damon/_damon_sysfs: support obsolete_target file drgn_dump_damon_status: dump damon_target->obsolete sysfs.py: extend assert_ctx_committed() for monitoring targets selftests/damon/sysfs: add obsolete_target test .../ABI/testing/sysfs-kernel-mm-damon | 7 +++ Documentation/admin-guide/mm/damon/usage.rst | 13 +++-- include/linux/damon.h | 6 +++ mm/damon/core.c | 10 +++- mm/damon/sysfs.c | 51 ++++++++++++++++++- tools/testing/selftests/damon/_damon_sysfs.py | 11 +++- .../selftests/damon/drgn_dump_damon_status.py | 1 + tools/testing/selftests/damon/sysfs.py | 48 +++++++++++++++++ 8 files changed, 140 insertions(+), 7 deletions(-) base-commit: a3e008fdd7964bc3e6d876491c202d476406ed59 -- 2.47.3
