Re: [PATCH] mm: migrate: requeue destination folio on deferred split queue

[Matthew Wilcox]

On Fri, Mar 06, 2026 at 05:12:38PM +0300, Usama Arif wrote:
> +       /*
> +        * Record whether the source folio is on the deferred split queue
> +        * before move_to_new_folio(), which unqueues it via
> +        * __folio_migrate_mapping().
> +        */
> +       if (folio_test_large(src) && folio_test_large_rmappable(src) &&
> +           !data_race(list_empty(&src->_deferred_list)))

Why do you need data_race() here?  list_empty() contains a READ_ONCE()
so shouldn't be necessary?

> +               old_page_state |= PAGE_WAS_ON_DEFERRED_SPLIT;

You've done a great job of the naming.  So much so that the comment
seems entirely unnecessary?

> +       /*
> +        * Requeue the destination folio on the deferred split queue if
> +        * the source was on the queue.  The source is unqueued in
> +        * __folio_migrate_mapping(), so we record and check the state
> +        * from before move_to_new_folio().
> +        */
> +       if (old_page_state & PAGE_WAS_ON_DEFERRED_SPLIT)
> +               deferred_split_folio(dst, false);

Again, I'm not sure the comment says anything that the code doesn't?