todo

TODOs
=====

WIP
---

merged in mm
- Handle non-power-of-two min_nr_regions aligning.
  - ALIGN() is only for power of two alignment.
  - merged in mm.git
- per-filtered-address-ragne prioritization
  - do the temperature-prioritization for address filter-passed regions,
    separately
  - merged in mm.git
- respect min_nr_regions from beginning
  - merged in mm.git
- fix sampling intervals overflow
- add CONFIG_DAMON_HARDENED for integrity checking
- allow stop-after-achieving DAMOS goal
  - add per-goal quota tuning strategy
    - consist: the current one, default.
    - temporal: the new one.
    - bpf: for future?
- fix walk_system_ram() type violation
  - https://lore.kernel.org/20260129161029.48991-1-sj@kernel.org

- mark DAMOS filters/ dir deprecated on doc
- cover all physical address space from DAMON modules
- add kdamond_pid to damon_stat.
- let DAMON_RECLAIM auto-tune intervals.
- kdamond pause/resume.
  - Use it for drgn tests.
- Let DAMOS action failed region be charged in a different rate
  - e.g., charge only 1 byte for 1 MiB of failed region.

- Documentation cleanup: Make link from design to API
- deprecate sysfs filters/ in favor of {core,ops}_filters/
  - warn on use of filters/, by 2027
  - rename filters/ to filters_DEPRECATED/, by 2028
  - remove filters/ code and documentation, by 2029

- counters of interests
  - for production level lightweight page-level monitoring
  - let users register counters of interests
  - when doing access check, check if the sample page is of the interest,
    increase the counter.
  - users know how many of each region is of the type, proportionally.
  - nr_accesses will be the default counter

- Sashiko bug findings
  - damon_..._enabled_store() NULL deref on init failure
    - https://lore.kernel.org/20260419014800.877-1-sj@kernel.org
  - repeat_call_control leak on premature DAMON stop
    - https://lore.kernel.org/20260319155742.186627-5-objecting@objecting.org
    - merged in mm
  - damos_walk_cancel() deadlock.
    - https://lore.kernel.org/20260322170700.83123-1-sj@kernel.org
    - patch posted
  - damon_call() cleanup deadlock.
    - https://lore.kernel.org/20260325141956.87144-1-sj@kernel.org
    - patch posted
  - validate quota goal nid
    - https://lore.kernel.org/20260325155221.202700-1-objecting@objecting.org
    - patch posted
  - charged_from wraparound during DAMOS deactivation/ctx pause
    - https://lore.kernel.org/20260324040722.57944-1-sj@kernel.org
    - patch posted
  - race between module params and commit_inputs
    - divide by zero of damon_reclaim_new_scheme()
      - https://lore.kernel.org/20260319161620.189392-3-objecting@objecting.org
    - cache addr_unit using READ_ONCE(), on DAMON_RECLAIM and DAMON_LRU_SORT.
      - https://lore.kernel.org/20260319161620.189392-2-objecting@objecting.org
    - patch posted
  - damos_stat damon_call() failure memory leak
    - https://lore.kernel.org/20260401012428.86694-1-sj@kernel.org
    - patch posted
      - https://lore.kernel.org/20260402134418.74121-1-sj@kernel.org
  - zero throughput-causing permanent damos deactivation on time quota use case
    - https://lore.kernel.org/20260405192504.110014-1-sj@kernel.org
    - patch posted
      - https://lore.kernel.org/20260407003153.79589-1-sj@kernel.org
  - min_region_sz power_of_2() validation for damon_sysfs_turn_on()
    - https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org
    - patch posted
      - https://lore.kernel.org/20260411213638.77768-1-sj@kernel.org

  - make damon_sysfs_next_updte_jiffies per-context
    - https://lore.kernel.org/20260319155742.186627-5-objecting@objecting.org
  - pid leak on damon_commit_ctx()
    - https://lore.kernel.org/20260319155742.186627-2-objecting@objecting.org

    - think about age wrap around to 0.
      - https://lore.kernel.org/20260319161620.189392-3-objecting@objecting.org
    - avoid divide-by-zero in damos_get_node_mem_bp() dueo ti zero i.totalram
      - https://lore.kernel.org/20260328133216.9697-1-sj@kernel.org
    - underflow of numerator in damos_get_node_memcg_used_bp()
      - https://lore.kernel.org/20260329154813.47382-1-sj@kernel.org
    - avoid divide-by-zero in damos_get_node_memcg_used_bp()
      - https://lore.kernel.org/20260329154813.47382-1-sj@kernel.org
    - mult_frac() in damos_get_node_memcg_used_bp() overflow on 32bit
      - https://lore.kernel.org/20260329154813.47382-1-sj@kernel.org
    - allow force-restart of DAMON_RECLAIM/LRU_SORT
      - https://lore.kernel.org/20260410135500.81989-1-sj@kernel.org
      - Liew is working
        - https://lore.kernel.org/20260411000458.11479-1-aethernet65535@gmail.com
    - cleanup !sz case in damon_do_apply_schemes()
      - https://lore.kernel.org/20260410233223.88212-1-sj@kernel.org
    - Think about damon_start() partial failures
      - https://lore.kernel.org/20260411233431.78220-1-sj@kernel.org
    - damon_stat stale kdamond_pid
      - https://lore.kernel.org/20260414053742.90296-1-sj@kernel.org
    - module init and parameter set race causing NULL dereference
      - https://lore.kernel.org/20260418153656.834-1-sj@kernel.org

Planning / Considering
----------------------

- Aware 1 GiB hugetlb pages when auto-tuning intervals.
  - Subtract 1 GiB hugetlb pages from the total size of memory.
- Let DAMON_STAT and DAMON_RECLAIM run in parallel.
  - Let DAMON API callers share a kdamond
  - What kdamond to share?
    - A single one that always running, say, kdamond*<N>?
    - Just the kdamond of the first caller that started (could be any
      kdamond<N>?
- add drgn selftests for DAMON modules.
- Support tlb flushing
  - https://lore.kernel.org/all/a2fb10bd-b44a-350e-f693-82ecfa6f54a8@huawei.com/
- automatic paddr regions detection
  (handle hot(un)plugged memory regions)
  - similar to vaddr, detect and cover all online memory as much as possible,
    with a few holes.
- make DAMON_STAT cover multiple hot-[un]pluggable NUMA nodes
  - implement and use kind of three big regions detection mechanism
- distinction of uncheckable memory
  - not just say it is not accessed, but disclose the fact that it was unable
    to check the access to, and apply merge-split with the fact.
- add kunit test for all parameters commit functions
- add damos_stat for auto-tuned zero size applying

- DAMOS_KILL: DAMON-based OOM killing
  - If DAMON_RECLAIM doesn't increase free memory, killing processes of hot
    pages.
- implement pause/resume of kdamonds
  - Or, let user feed nr_accesses and age of regions
    - User can snapshot the last monitoring results and continue monitoring
      from the status.

- support (multiple) kdamosd
- per-noe memory bandwidth utilization DAMOS quota goal metric
- clarify possible monitoring results loss on usage doc.
- implement addr_unit commit kunit test
- implement addr_unit to/from core address conversion kunit test
- handle charged_ns overflow on 32bit machines
- cleanup damon_set_attrs() documentation
- add kunit test for damon_call() and damos_walk()
- DAMON-based khugepaged
  - Make khugepaged listen DAMON's voice when collapsing
- Support multi contexts per kdamond
- Add sharable kdamond
  - Run with auto-tuned intervals
  - Let API callers report access information, read monitoring results and
    add/remove DAMOS schemes
    - Major callers would be DAMON modules
    - damon_get_handle(), damon_report_access(), damos_add_folios()
  - Let ABI users read monitoring results and DAMOS stat
    - /sys/kernel/mm/damon/???/
- DAMON_NUMA_MIGRATE
  - Aim for not only traditional NUMA but also tiering
  - Just extend mtier to every node, but CPU-aware.
- sysfs command for updating params (for restoring old params)
- write a selftest for sz_filter_passed
- contigurized-vddr
  - trat end of a discrete region as start of next region
  - connect regions before and after huge unmapped area
  - connect regions of different virtual addresses
- Write API documentation
  - no just kerenl doc, but more structured document is needed
- Let users decide regions split factor
  - https://lore.kernel.org/20241026215311.148363-1-sj@kernel.org
- Let users periodically split regions without per-region subregions limit
  - https://lore.kernel.org/20241026215311.148363-1-sj@kernel.org
- Sampling based page level properties based monitoring
  - For DAMOS_STAT, do sampling for sz_filter_passed calculation
    - Let user sets the number of samples per region for this
- Support reserved uninstall of DAMOS
  - Allow running DAMOS scheme for only specific apply intervals
- Extend for memory bandwidth monitoring
- Extend for AMD IBS-based monitoring
- Extend for cache-set space monitoring
- Extend for cache-line space monitoring
  - Require sub-page level monitoring (IBS?)
- Access/Contiguity-aware Memory Auto-scaling
  - https://lore.kernel.org/damon/20240512193657.79298-1-sj@kernel.org
- Support cleaning sysfs input files up to committed values
- holistic heterogenous memory management
  - address CPU-numa, CXL-numa, and device(e.g., GPU)-numa nodes
- DAMON_LRU_SORT auto-tuning
  - Let auto-tuning using active/inactive memory ratio
- Selftests: Test DAMON online tuning
- Selftests: Test DAMOS online tuning
- Selftests: Test DAMOS filter
- Make 'age' counted by sample_interval rather than aggregation interval
- CPU time quota for DAMON monitirng
- monitoring part CPU usage statistics
- Setting resolution of damos tried_regions
  - Should be able to control the directories population overhead when the
    number of regions is big
- More DAMON modules
  - DAMON-based THP hinting module
- rename nr_accesses/moving_accesses_bp
- mark nr_accesses as private
- use a dedicated struct for access rate
- let kdamond name be user-defined
- let DAMON modules share one kdamond
- unify DAMON modules
- support multiple contexts per kdamond
- DAMON-based VMA split/merge
  - Help big VMA contention issue?
  - We can further expose the monitoring results via vma name
  - Reading results becomes very easy
- Contig memory access util monitoring
- WSS/RSS based processes sorting
- LRU-based monitoring ops
- Fixed granularity idleness monitoring
  - Must be useful for further DAMON overhead/accuracy evaluation
- Improve regions-based monitoring quality
- Support cgroups
- Add __counted_by() annotation when ready
  (https://lore.kernel.org/r/CAKwvOdkvGTGiWzqEFq=kzqvxSYP5vUj3g9Z-=MZSQROzzSa_dg@mail.gmail.com)
- Ideas from LSFMM
  - Add operations driven access check
    - Let it calls DAMON functions for noticed access and then let DAMON records
      the access
  - Take care of fairness on ACMA (e.g., NUMA)
- Consider hugetlb handling optimization
  - DAMON_RECLAIM will meaninglessly try reclaiming hugetlb pages, consume
    CPUs.  Find a way to optimize.
- DAMON in process context
  - Do the monitoring for each process in task_work context, like NUMA
    balancing installs prot_none.

Frozen
------

Recently Done
-------------

- DAMOS stat/control improvement
  - Show how many snapshots the scheme has processed
  - Let DAMOS deactivated based on the number of processed snapshots
  - Provide a tracepoint for DAMOS stat
  - merged into 7.0-rc1
- DAMON_LRU_SORT modernization
  - merged into 7.0-rc1
- hide kdamond and kdamond_lock from API callers
  - merged into 7.0-rc1
- modernize wss_estimation kselftest
  - merged into 7.0-rc1
- document modules usage on usage doc
  - merged into 7.0-rc1


Non-DAMON issues
----------------