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

[Christoph Hellwig]

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.