linux-kernel - Re: [PATCH v2 0/6] Enhance union-find with KUnit tests and optimization improvements

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Message-ID: <1ccd6411-5002-4574-bb8e-3e64bba6a757@redhat.com>
Date: Wed, 9 Oct 2024 10:53:08 -0400
From: Waiman Long <llong@...hat.com>
To: Kuan-Wei Chiu <visitorckw@...il.com>,
 Christoph Hellwig <hch@...radead.org>
Cc: xavier_qy@....com, lizefan.x@...edance.com, tj@...nel.org,
 hannes@...xchg.org, mkoutny@...e.com, akpm@...ux-foundation.org,
 jserv@...s.ncku.edu.tw, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v2 0/6] Enhance union-find with KUnit tests and
 optimization improvements

On 10/9/24 10:13 AM, Kuan-Wei Chiu wrote:
> On Wed, Oct 09, 2024 at 02:09:51AM -0700, Christoph Hellwig wrote:
>> On Mon, Oct 07, 2024 at 11:28:27PM +0800, Kuan-Wei Chiu wrote:
>>> This patch series adds KUnit tests for the union-find implementation
>>> and optimizes the path compression in the uf_find() function to achieve
>>> a lower tree height and improved efficiency. Additionally, it modifies
>>> uf_union() to return a boolean value indicating whether a merge
>>> occurred, enhancing the process of calculating the number of groups in
>>> the cgroup cpuset.
>> Given that this fairly special union find code is obly used in the
>> cpuset code, please move the code there rather adding more exports.
>> Even as-is it is bloating every kernel build even without cgroups
>> for no good reason.
>>
> I noticed that it was Michal who originally suggested putting the
> union-find code to lib/ in an earlier email thread [1]. Before I send a v3
> patch moving it to cpuset, I'd like to hear Michal, Tejun, and Waiman’s
> thoughts on this change.
>
> [1]: https://lore.kernel.org/lkml/wu4m2m5igc752s5vrmtsnd7ekaq6opeqdtrzegs7oxlwgypdcx@qhcnow5txxiv/
>
> Regards,
> Kuan-Wei

The current union_find code is pretty small. Putting it there in lib 
allows it to be used by other kernel subsystems when needed. I believe 
it should stay in lib. If a slight increase in kernel size is a concern, 
we can update the Makefile to make its build depend on CONFIG_CPUSETS 
which can be taken out when it is being used by another kernel subsystem.

Cheers,
Longman