Re: (sashiko review) [RFC PATCH v5 01/10] mm/damon/core: introduce damon_ctx->paused

[SeongJae Park <sj@kernel.org>]

On Mon, 23 Mar 2026 21:07:21 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Mon, 23 Mar 2026 18:28:00 -0700 SeongJae Park <sj@kernel.org> wrote:
> 
> > Forwarding Sashiko review for doing discussions via mails.
[...]
> > Additionally, when the context is paused, kdamond_fn remains in this sleep
> > loop and skips calling damos_adjust_quota(), which means quota->charged_from
> > is frozen.
> > 
> > If the pause lasts for more than LONG_MAX jiffies (e.g., about 24.8 days on
> > a 32-bit system with HZ=1000), will system jiffies wrap past the half-range
> > limit of the unsigned long type relative to the frozen timestamp?
> > 
> > If this wraparound occurs, time_after_eq(jiffies, quota->charged_from +
> > interval) would evaluate to false when unpaused. Would this cause the quota
> > window to not reset for another 24.8 days, accumulating charged_sz and
> > blocking the scheme from being applied?
> 
> That's a wild corner case, but I agree it is better to avoid the problematic
> case.  I'm still thinking about the good way for that.  Anyway, I will address
> this in the next spin.

The root cause of the issue was introduced before this patch, so I fixed it
with another hotfix [1].  So next spin of this patch will have no change.

[1] https://lore.kernel.org/20260329152306.45796-1-sj@kernel.org


Thanks,
SJ

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