Re: [PATCH v2 0/2] mm/damon: preserve temporal quota state for unmeasured PSI goals

[SJ Park <sj@kernel.org>]

On Mon, 21 Sep 2026 04:00:11 +0200 Karl Mehltretter <kmehltretter@gmail.com> wrote:

> A PSI quota goal without a previous sample is scored as achieved. This
> leaves the consist tuner's input unchanged but sets the temporal quota
> to zero. Preserve the temporal tuner's previous goal-achievement state
> using its effective quota, as SJ suggested [1], and test the helper with
> explicit PSI totals.
> 
> All 42 DAMON KUnit tests pass on x86-64 and i386. With the original
> scoring retained in the extracted helper, the new test fails on both.
> In a live damo test, a goals-only update changes a running 64 KiB quota
> to zero for an unmeasured round without the fix. With the fix, the
> effective quota stays at 64 KiB. A full damo tune also needs the separate
> quota-reset fix [3], so the context update preserves the running quota
> used for this decision.
> 
> DAMON selftests show no new failures (QEMU TCG guest; the wss_estimation
> test misses its accuracy bounds with and without the fix).
> 
> Changes since v1 [2]:
>  - Use the previous effective quota for the temporal decision, including
>    when it is zero. Keep resetting last_psi_total for new and updated
>    goals.
>  - Move the current-value calculation and last_psi_total update into a
>    helper. Test both tuners with explicit samples and check
>    last_psi_total after each call.
> 
> The series is based on mm-new as of September 20.
> 
> [1] https://lore.kernel.org/damon/20260916001311.101024-1-sj@kernel.org/
> [2] https://lore.kernel.org/20260915060937.3423-1-kmehltretter@gmail.com/
> [3] https://lore.kernel.org/20260921003047.12041-1-kmehltretter@gmail.com/

The patch 1 has wrong Fixes: tag, as I replied to it with two options to path
forward.  Speculatively assuming your preferrence is option 2 (adding this
series with fixed 'Fixes:' tag), I applied this series to damon/next [1] tree
with the suggested Fixes: tag modification.  Let me know if you want the
options 1 (squash it into the incomplete fix [2] before it is merged into the
mainline).

Unless you want option 1, and if this series is not added to mm.git in short
term (~1 week?) with option 1 update, I will ask mm.git maintainer (Andrew
Morton) to pick this.  So, no action from your side is needed for now unless
you want option 1.  If it seems I forgot doing that or you cannot wait for my
action, please feel free to ping me or Andrew.

[1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees
[2] commit b73198a47ffe ("mm/damon/core: handle uninitialized damos_quota_goal->last_psi_total")


Thanks,
SJ

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