Re:Re: [PATCH] mm/damon/core: reject zero sample_interval

At 2026-07-22 22:01:13, "SJ Park" <[email protected]> wrote:
>Hello liyouhong,
>
>
>Thank you for sharing this patch!
>
>On Wed, 22 Jul 2026 17:43:04 +0800 [email protected] wrote:
>
>> From: liyouhong <[email protected]>
>> 
>> damon_set_attrs() allows sample_interval == 0.  Sysfs likewise accepts
>> sample_us=0.  kdamond_fn() then calls kdamond_usleep(0) every loop
>> iteration, so kdamond busy-spins and can peg a CPU.
>> 
>> With a zero sampling interval the access-rate accounting also diverges:
>> nr_accesses_bp no longer matches nr_accesses * 10000, and
>> kdamond_reset_aggregated() hits:
>> 
>>   WARNING: invalid nr_accesses_bp at reset: ...
>
>The warning has removed by nr_accesses_bp optimization patch series, which is
>currently queued for 7.3-rc1.  So the warning will not be triggered on near
>future mainline.
>> 
>> Reject sample_interval == 0 in damon_set_attrs(), which covers sysfs
>> commit and other callers.  damon_lru_sort already refused a zero
>> sample_interval; align the core validation with that.
>
>This is a sort of behavioral change.  I also feel this adds another corner case
>that makes my head complicated.  There are a few logic written under the
>assumption of zero intervals.  Having inconsistencies between allowed input and
>handling logic will make it difficult to maintain in long term.  Can't we keep
>supporting zero sample interval and fix the warning or the real bug instead?
>




Hi SJ,

Thanks for the explanation. I agree rejecting zero sample_interval
is the wrong approach, especially since the warning will be gone with
your queued series.


Thanks,
liyouhong