Re: [PATCH 1/2] mm/damon/core: modified and tunning damon_split_regions_of()

JaeJoon Jung
2026-01-14T20:19:03Z

On Thu, 15 Jan 2026 at 00:46, SeongJae Park <sj@kernel.org> wrote:
>
> Hello JaeJoon, thank you for continued interest in DAMON.
>
> On Tue, 13 Jan 2026 21:16:42 +0900 JaeJoon Jung <rgbi3307@gmail.com> wrote:
>
> > Before modification:
> > sz_region
> > |--------|--------|--------||--------|--------|--------|--------|
> > nr_subs: 1 2 3 4 5 9
> > split random: <----------- (*] randmon LOST -------------->
> >
> > When dividing sz_region at rand, the random value may be small, such as
> > 1 or 2. At this time, there is a problem that only the front areas
> > corresponding to 1 and 2 are divided, and the remaining back area
> > becomes too wide. If the area is too wide, there will be many missed
> > address access judgments.
> >
> > After modification:
> > sz_region
> > |--------|--------|--------|--------|--------|--------|--------||
> > nr_subs: 1 2 3 4 5 9
> > split from <------------ (sz_region / nr_subs) ------------------>
> >
> > It is recommended to divide sz_region evenly in the ratio (sz_region /
> > nr_subs) rather than using rand. In this way, if you decide nr_subs well,
> > you can logically match the number of divisions and their sizes.
>
> I was thinking about how to reply to this patch. Since it is taking unusually
> long time, let me add short comments for direct future of this patch.

After much thought, you ask a simple question below.

>
> The existing code uses random() for a reason. This change might break it. Can
> you further explain what was the point of the use of random(), and why this
> change is not breaking it?

To find a needle in a haystack, is it right to keep poking around randomly?

>
> >
> > Signed-off-by: JaeJoon Jung <rgbi3307@gmail.com>
>
> Unless you can give me a convincing answer to my above question,
>
> Nacked-by: SeongJae Park <sj@kernel.org>
>
> Same for your followup patch [1]. Btw, please send patches of same series as
> one thread from next time.

I sent you two after much deliberation so that you can see them clearly.

Thanks,
JaeJoon

>
> [1] https://lore.kernel.org/20260113121731.31468-1-rgbi3307@gmail.com
>
>
> Thanks,
> SJ
>
> …