Hello,

This patch series provides two performance optimizations for the DAMON
core, specifically targeting the hot paths in kdamond.

The first patch optimizes kdamond_apply_schemes() by inverting the loop
order. By iterating over schemes first and regions second, we can
evaluate scheme-level invariants (like activation status and quotas)
once per scheme rather than for every single region. This significantly
reduces CPU overhead when multiple schemes are present or when quotas
are reached.

The second patch eliminates a hardware integer division in
damon_max_nr_accesses() by using the pre-cached aggr_samples value.
Since this function is called once per region per sampling interval,
removing the division provides a measurable reduction in CPU cycles
spent in the access rate update path.

Changes from v1:
- Use min_t(unsigned long, ...) in damon_max_nr_accesses() to satisfy
  checkpatch warnings and improve readability.

Josh Law (2):
  mm/damon/core: optimize kdamond_apply_schemes() by inverting scheme
    and region loops
  mm/damon/core: eliminate hot-path integer division in
    damon_max_nr_accesses()

 include/linux/damon.h |  3 +-
 mm/damon/core.c       | 68 ++++++++++++++++++-------------------------
 2 files changed, 29 insertions(+), 42 deletions(-)

-- 
2.43.0

I show you already posted v3 [1] of this series.  So I'm skipping this version.

[1] https://lore.kernel.org/20260322214325.260007-1-objecting@objecting.org


Thanks,
SJ

On Sun, 22 Mar 2026 21:36:29 +0000 Josh Law <objecting@objecting.org> wrote:

> Hello,
> 
> This patch series provides two performance optimizations for the DAMON
> core, specifically targeting the hot paths in kdamond.
> 
> The first patch optimizes kdamond_apply_schemes() by inverting the loop
> order. By iterating over schemes first and regions second, we can
> evaluate scheme-level invariants (like activation status and quotas)
> once per scheme rather than for every single region. This significantly
> reduces CPU overhead when multiple schemes are present or when quotas
> are reached.
> 
> The second patch eliminates a hardware integer division in
> damon_max_nr_accesses() by using the pre-cached aggr_samples value.
> Since this function is called once per region per sampling interval,
> removing the division provides a measurable reduction in CPU cycles
> spent in the access rate update path.
> 
> Changes from v1:
> - Use min_t(unsigned long, ...) in damon_max_nr_accesses() to satisfy
>   checkpatch warnings and improve readability.
> 
> Josh Law (2):
>   mm/damon/core: optimize kdamond_apply_schemes() by inverting scheme
>     and region loops
>   mm/damon/core: eliminate hot-path integer division in
>     damon_max_nr_accesses()
> 
>  include/linux/damon.h |  3 +-
>  mm/damon/core.c       | 68 ++++++++++++++++++-------------------------
>  2 files changed, 29 insertions(+), 42 deletions(-)
> 
> -- 
> 2.43.0

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