Re: [PATCH 05/12] mm/damon/sysfs: remove probes number validation

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From: Kunwu Chan <kunwu.chan@gmail.com>
To: SJ Park <sj@kernel.org>
Cc: Kunwu Chan <kunwu.chan@linux.dev>,
	Kunwu Chan <kunwu.chan@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	damon@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 05/12] mm/damon/sysfs: remove probes number validation
Date: Wed,  2 Sep 2026 23:33:33 +0800	[thread overview]
Message-ID: <20260902153334.4034394-1-kunwu.chan@linux.dev> (raw)
In-Reply-To: <20260902143706.88115-1-sj@kernel.org>

On Wed,  2 Sep 2026 07:37:06 -0700 SJ Park <sj@kernel.org> wrote:

> On Wed,  2 Sep 2026 22:07:13 +0800 Kunwu Chan <kunwu.chan@gmail.com> wrote:
> 
> > On Tue,  1 Sep 2026 22:47:38 -0700 SJ Park <sj@kernel.org> wrote:
> [...]
> > I was wondering whether DAMON_MAX_PROBES is purely a core invariant
> > or also an interface constraint.
> 
> Thank you for reviewing my patch and raising this question!
> 
> > 
> > With this change, sysfs allows nr_probes larger than
> > DAMON_MAX_PROBES and damon_sysfs_probes_add_dirs() will start creating
> > probe objects before the configuration is later rejected by
> > damon_valid_probe_params().
> > 
> > Since nr_probes directly controls the number of sysfs objects created,
> > do we still want to keep an early check here?
> > 
> > I agree that the core validation is required for non-sysfs callers,
> > but I am not sure whether this particular limit should be duplicated
> > at the sysfs layer.
> 
> I agree the user experience may be not that good.
> 
> In my humble opinion, however, keeping code simplicity is more important than
> the user experience here.  After all, DAMON_SYSFS is recommended to be used by
> another high level tools like DAMON user-space tool (damo) rather than human
> fingers.  The user-space tools like damo can do the early check.
> 
> Please feel free to let me know if you have any other opinions or questions.

Hi SJ,

Thanks for the explanation.

I agree that keeping the invariant validation in the core layer avoids
duplicating the limit in multiple places.  Your point about DAMON_SYSFS
being mainly consumed by higher-level tools like damo also makes sense.

My concern was mainly about the temporary creation of sysfs probe objects
before the configuration is rejected, rather than the user-facing error
message.  Given that the number of probes is bounded by the core
invariant anyway, I agree that keeping the validation centralized is a
reasonable trade-off.

Thanks for clarifying.

Reviewed-by: Kunwu Chan <kunwu.chan@gmail.com>

Thanks,
Kunwu

> 
> 
> Thanks,
> SJ
> 
> [...]
> 

Sent using hkml (https://github.com/sjp38/hackermail)

next prev parent reply	other threads:[~2026-09-02 15:33 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-02  5:47 [PATCH 00/12] mm/damon: cleanup code, add test cases, and update guidances in docs SJ Park
2026-09-02  5:47 ` [PATCH 01/12] mm/damon/core: use damon_nr_samples_per_aggr() for max merge threshold SJ Park
2026-09-03  2:00   ` Kunwu Chan
2026-09-02  5:47 ` [PATCH 02/12] mm/damon/core: remove debug messages SJ Park
2026-09-02  6:14   ` SJ Park
2026-09-02  5:47 ` [PATCH 03/12] mm/damon/vaddr: remove a debug message SJ Park
2026-09-03  2:24   ` Kunwu Chan
2026-09-02  5:47 ` [PATCH 04/12] mm/damon/core: validate number of probes in valid_probe_params() SJ Park
2026-09-02 15:32   ` Kunwu Chan
2026-09-02  5:47 ` [PATCH 05/12] mm/damon/sysfs: remove probes number validation SJ Park
2026-09-02 14:07   ` Kunwu Chan
2026-09-02 14:37     ` SJ Park
2026-09-02 15:33       ` Kunwu Chan [this message]
2026-09-02  5:47 ` [PATCH 06/12] mm/damon/tests/core-kunit: extend set_regions() test for error case SJ Park
2026-09-02  5:47 ` [PATCH 07/12] mm/damon/tests/core-kunit: test <=0 size damon_set_regions() inputs SJ Park
2026-09-02  5:47 ` [PATCH 08/12] mm/damon/tests/core-kunit: test overlapping ranges for set_regions() SJ Park
2026-09-03  3:04   ` Kunwu Chan
2026-09-02  5:47 ` [PATCH 09/12] mm/damon/tests/core-kunit: test damon_nr_samples_per_aggr() SJ Park
2026-09-02 15:08   ` Kunwu Chan
2026-09-02 15:19     ` SJ Park
2026-09-02 15:49       ` Kunwu Chan
2026-09-03  0:22         ` SJ Park
2026-09-02  5:47 ` [PATCH 10/12] selftests/damon/sysfs.sh: test hugepage_mem_bp quota goal SJ Park
2026-09-03  3:06   ` Kunwu Chan
2026-09-02  5:47 ` [PATCH 11/12] Docs/mm/damon/maintainer-profile: update AI review for Sashiko replies SJ Park
2026-09-02  5:47 ` [PATCH 12/12] Docs/ABI/damon: recommend subsystem doc instead of admin-guide SJ Park
2026-09-03  3:09   ` Kunwu Chan
2026-09-02  6:16 ` [PATCH 00/12] mm/damon: cleanup code, add test cases, and update guidances in docs SJ Park
2026-09-02 22:42 ` Andrew Morton

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