[DAMON][Question] DAMON_STAT and DAMON_LRU_SORT module parameter conflict?

[DAMON][Question] DAMON_STAT and DAMON_LRU_SORT module parameter conflict?

[Liew Rui Yan]

TL;DR
=====
When CONFIG_DAMON_STAT_ENABLED_DEFAULT=y, enabling damon_lru_sort via sysfs
"enabled" parameter returns -EBUSY. Is this expected behavior? If yes, should
this limitation be documented?

Reproduction
============
Environment:
- Kernel: 7.0.0-rc3+ (x86_64)
- VM: Virtme-ng (4G RAM, 2 CPUs)
- Config: CONFIG_DAMON_STAT_ENABLED_DEFAULT=y, CONFIG_DAMON_LRU_SORT=y

Steps:
1. cd /sys/module/damon_lru_sort/parameters
2. (optional) tune parameters: hot_thres_access_freq, cold_min_age, etc.
3. echo Y > enabled

Result:
  bash: echo: write error: Device or resource busy

Workaround:
  Disable CONFIG_DAMON_STAT_ENABLED_DEFAULT, or disable damon_stat at runtime
  before enabling damon_lru_sort.

Questions
=========
1. Is this resource conflict between damon_stat and damon_lru_sort expected?
2. If yes, should this limitation be documented in:
   - Documentation/admin-guide/mm/damon/lru_sort.rst
   - Documentation/admin-guide/mm/damon/stat.rst

Additional Context
==================
- On major distros (Arch/Fedora), CONFIG_DAMON_STAT_ENABLED_DEFAULT is typically
  unset (disabled), so this issue may not affect most users.
- However, for kernel developers or custom builds enabling both modules, clearer
  documentation or error handling would improve debuggability.

Best regards,
Liew Rui Yan

Re: [DAMON][Question] DAMON_STAT and DAMON_LRU_SORT module parameter conflict?

[SeongJae Park]

On Fri, 13 Mar 2026 19:09:53 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> TL;DR
> =====
> When CONFIG_DAMON_STAT_ENABLED_DEFAULT=y, enabling damon_lru_sort via sysfs
> "enabled" parameter returns -EBUSY. Is this expected behavior? If yes, should
> this limitation be documented?

Seems this is a duplicate of another similar question [1].  I believe our
discussion on the thread answers this.

[1] https://lore.kernel.org/20260313111702.38667-1-aethernet65535@gmail.com


Thanks,
SJ

[...]

Re: [DAMON][Question] DAMON_STAT and DAMON_LRU_SORT module parameter conflict?

[Liew Rui Yan]

On Sat, Mar 14, 2026 at 8:51 AM SeongJae Park <sj@kernel.org> wrote:
>
> Seems this is a duplicate of another similar question [1].  I believe our
> discussion on the thread answers this.
>

Hi SeongJae,

Thanks for pointing it out. You're right, this is a duplicate.

This was my first version, but I resent it because I realized I had the
wrong CC list (I typed damon@list.linux.dev, missing a 's') and it
didn't show up on lore.kernel.org immediately, which led me to believe
the first attempt had failed.

Sorry for the noise.

Best regards,
Liew Rui Yan