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

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Message-ID: <20260116031826.72372-1-sj@kernel.org>
Date: Thu, 15 Jan 2026 19:18:25 -0800
From: SeongJae Park <sj@...nel.org>
To: JaeJoon Jung <rgbi3307@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	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 05:18:51 +0900 JaeJoon Jung <rgbi3307@...il.com> wrote:

> 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.

Unfortunately what I asked are still not clearly answered to me.  And based on
our past conversations including the recent one that I acknowledged as a
communication failure [1] and this thread, I expect asking you more questions
will not work for me.  I don't think that's someone's fault, but obviously
that's the current situation.  I will not ask you more questions for the
reason, unless I get a reason to change my mind.

So, to make it crystal clear, for this patch and the one you posted together,

Nacked-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

[1] https://lore.kernel.org/20260101224420.73826-1-sj@kernel.org

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