Re: [PATCH] mm/damon/core: set initial quota->charged_from to INITIAL_JIFFIES

[SeongJae Park <sj@kernel.org>]

Hello Sang-Heon,

On Tue, 19 Aug 2025 03:38:03 +0900 Sang-Heon Jeon <ekffu200098@gmail.com> wrote:

> Kernel initialize "jiffies" timer as 5 minutes below zero, as shown in
> include/linux/jiffies.h
> 
>  /*
>   * Have the 32 bit jiffies value wrap 5 minutes after boot
>   * so jiffies wrap bugs show up earlier.
>   */
>   #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
> 
> In 32bit system, if quota->charged_from is initialized to 0 as it now,
> it will not adjust event if reset_interval_ms passes for the first 5
> minutes.

jiffies is unsigned.  Hence the initial invocation of time_after_eq() in
damos_adjust_quota(), which is the only place reading quota->charged_from, will
return 'true' and the quota adjustment would be done without delay, unless the
scheme apply interval is unrealistically big.

Please let me know if I'm missing something.


Thanks,
SJ

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