DAMOS fitlers are exclusive filters. It only excludes memory of specific types from the DAMOS action targets. This has below problems. First, the name is not explicitly explaining the behavior. This actually resulted in confusions[1] and works to improve the siaution[2], including wordsmithing documentations and adding features to DAMON user-space tool, damo. Secondly, the functionality is restrictive. This is especially problematic when multiple filters need to be used. For example, building a DAMOS scheme that applies the action to memory that belongs to cgroup A "or" cgroup B is impossible. A workaroudn is using two schemes, each filtering out memory that not belong to cgroup A and cgroup B, respectively. It is cumbersome, and makes control of quota-like additional factors difficult. Extend DAMOS filters to support not only excluding (blocking), but also including (pass-through) behavior. For the extension, add a new damos_filter struct field called 'pass' for DAMON kernel API users. Using the API, add a DAMON sysfs file of same name under DAMOS filter sysfs directory, for DAMON user-space ABI users. To prevent breaking old users with a behavioral change, set the blocking as the default behavior. Note that DAMOS' default behavior without DAMOS filters is applying the action to any memory. And DAMOS filters work for only memory that satisfies 'type' and 'matching'. Hence installing pass filter without any block filter after them makes no filter-behavioral change. [1] https://lore.kernel.org/20240320165619.71478-1-sj@xxxxxxxxxx [2] https://git.kernel.org/sj/damo/c/b6a722c85ff91e5abe9dd47135e300df243da056 SeongJae Park (10): mm/damon: fixup damos_filter kernel-doc mm/damon/core: add damos_filter->pass field mm/damon/core: support damos_filter->pass mm/damon/paddr: support damos_filter->pass mm/damon: add pass argument to damos_new_filter() mm/damon/sysfs-schemes: add a file for setting damos_filter->pass Docs/mm/damon/design: document pass/block filters behaviors Docs/ABI/damon: document DAMOS filter pass sysfs file Docs/admin-guide/mm/damon/usage: omit DAMOS filter details in favor of design doc Docs/admin-guide/mm/damon/usage: document DAMOS filter 'pass' sysfs file .../ABI/testing/sysfs-kernel-mm-damon | 14 +++-- Documentation/admin-guide/mm/damon/usage.rst | 55 ++++++++++--------- Documentation/mm/damon/design.rst | 29 ++++++++-- include/linux/damon.h | 15 +++-- mm/damon/core.c | 12 ++-- mm/damon/paddr.c | 9 +-- mm/damon/reclaim.c | 2 +- mm/damon/sysfs-schemes.c | 32 ++++++++++- mm/damon/tests/core-kunit.h | 14 ++--- 9 files changed, 125 insertions(+), 57 deletions(-) -- 2.39.5
