Re: [PATCH] mm/damon/core: trace esz at first setup

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 20 May 2026 08:03:10 -0700 SeongJae Park <sj@kernel.org> wrote:

> DAMON traces effective size quota from the second update, only if a
> change has been made by the update.  Tracing only changed updates was an
> intentional decision to avoid unnecessary same value tracing.  Always
> skipping the first value is just an unintended mistake.
> 
> The mistake makes the tracepoint based investigation incomplete, because
> the first effective size quota is never traced.  It is not a big issue
> when the 'consist' quota tuner is used, because it keeps changing the
> quota in the usual setup.
> 
> However, when the 'temporal' tuner is used, the quota value is not
> changed before the goal achievement status is completely changed.  For
> example, if the DAMOS scheme is started with an under-achieved goal, the
> quota is set to the maximum value, and kept the same value until the
> goal is achieved.  Because DAMON skips the first value, the user cannot
> know what effective quota the current scheme is using.  Only after the
> goal is achieved, the effective quota is changed to zero, and traced.
> 
> Unconditionally trace the initial quota value to fix this problem.
> 
> Note that the 'temporal' quota tuner was introduced by commit
> af738a6a00c1 ("mm/damon/core: introduce
> DAMOS_QUOTA_GOAL_TUNER_TEMPORAL"), which was added to 7.1-rc1.  But even
> with the 'consist' quota tuner, the tracing is unintentionally
> incomplete. Hence this commit marks the introduction of the trace event
> as the broken commit.

OK, but...

> Fixes: a86d695193bf ("mm/damon: add trace event for effective size quota")
> Cc: <stable@vger.kernel.org> # 6.17.x
> Signed-off-by: SeongJae Park <sj@kernel.org>

The patch is marked for backporting but it assumes the presence of
"mm/damon/core: make charge_addr_from aware of end-address
exclusivity", which is queued for 7.2-rc1.

We can either redo this against current -linus and fix up mm.git's
"mm/damon/core: make charge_addr_from aware of end-address exclusivity"
or we can queue this for 7.2-rc1 and you get to deal with fallout when
-stable maintainers hit issues backporting this.

Preferences?