Re: [PATCH] lib/list_sort: introduce list_sort_nonatomic() and remove dummy cmp() calls

From: Christoph Hellwig <hch@infradead.org>
To: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Richard Weinberger <richard@nod.at>,
	Andrew Morton <akpm@linux-foundation.org>,
	chengzhihao1 <chengzhihao1@huawei.com>,
	jserv@ccns.ncku.edu.tw, eleanor15x@gmail.com,
	marscheng@google.com, linux-mtd <linux-mtd@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] lib/list_sort: introduce list_sort_nonatomic() and remove dummy cmp() calls
Date: Tue, 17 Mar 2026 07:22:12 -0700	[thread overview]
Message-ID: <abljlKim3-hPngCG@infradead.org> (raw)
In-Reply-To: <abhGF65wCbI7CsTm@google.com>

On Tue, Mar 17, 2026 at 02:04:07AM +0800, Kuan-Wei Chiu wrote:
> I tried to dig into the history. It turns out this mechanism was
> introduced 16 years ago in commit 835cc0c8477f ("lib: more scalable
> list_sort()"). The commit message explicitly mentioned both XFS and
> UBIFS as the intended users for this long-list workaround. However,
> looking at the tree back then, XFS never actually put a cond_resched()
> in their cmp() function. It seems UBIFS has been the sole user of this
> trick ever since. Given that it has been this way for 16 years, it
> seems other subsystems haven't really encountered any practical issues
> with it.

.. or it wasn't even needed in the first place.

> For UBIFS, this patch doesn't alter the frequency, timing, or behavior
> of the cond_resched() calls at all, so I am confident that this won't
> introduce any regressions.

I'd be tempted to drop the workaround and remove the cond_resched
from ubifs given that entirely non-preemptible scheduling models are
on their way out.

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