linux-kernel - Re: [PATCH 1/2] mm/damon/core: modified and tunning damon_split_regions

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Message-ID: <CAHOvCC4kktZ5rvPmJKpeHkOznbmLAxB1GfowU7NgLc1EUA3-hQ@mail.gmail.com>
Date: Thu, 15 Jan 2026 05:18:51 +0900
From: JaeJoon Jung <rgbi3307@...il.com>
To: SeongJae Park <sj@...nel.org>
Cc: damon@...ts.linux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	rgbi3307@...e.com
Subject: Re: [PATCH 1/2] mm/damon/core: modified and tunning damon_split_regions_of()

On Thu, 15 Jan 2026 at 00:46, SeongJae Park <sj@...nel.org> wrote:
>
> Hello JaeJoon, thank you for continued interest in DAMON.
>
> On Tue, 13 Jan 2026 21:16:42 +0900 JaeJoon Jung <rgbi3307@...il.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@...il.com>
>
> Unless you can give me a convincing answer to my above question,
>
> Nacked-by: SeongJae Park <sj@...nel.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
>
> [...]