On 10/19/25 19:19, Wei Yang wrote:
> On Wed, Oct 01, 2025 at 04:57:02PM +1000, Balbir Singh wrote:
> [...]
>> static int __folio_split(struct folio *folio, unsigned int new_order,
>> struct page *split_at, struct page *lock_at,
>> - struct list_head *list, bool uniform_split)
>> + struct list_head *list, bool uniform_split, bool unmapped)
>> {
>> struct deferred_split *ds_queue = get_deferred_split_queue(folio);
>> XA_STATE(xas, &folio->mapping->i_pages, folio->index);
>> @@ -3765,13 +3757,15 @@ static int __folio_split(struct folio *folio,
>> unsigned int new_order,
>> * is taken to serialise against parallel split or collapse
>> * operations.
>> */
>> - anon_vma = folio_get_anon_vma(folio);
>> - if (!anon_vma) {
>> - ret = -EBUSY;
>> - goto out;
>> + if (!unmapped) {
>> + anon_vma = folio_get_anon_vma(folio);
>> + if (!anon_vma) {
>> + ret = -EBUSY;
>> + goto out;
>> + }
>> + anon_vma_lock_write(anon_vma);
>> }
>> mapping = NULL;
>> - anon_vma_lock_write(anon_vma);
>> } else {
>> unsigned int min_order;
>> gfp_t gfp;
>> @@ -3838,7 +3832,8 @@ static int __folio_split(struct folio *folio, unsigned
>> int new_order,
>> goto out_unlock;
>> }
>>
>> - unmap_folio(folio);
>> + if (!unmapped)
>> + unmap_folio(folio);
>>
>> /* block interrupt reentry in xa_lock and spinlock */
>> local_irq_disable();
>> @@ -3925,10 +3920,13 @@ static int __folio_split(struct folio *folio,
>> unsigned int new_order,
>>
>> next = folio_next(new_folio);
>>
>> + zone_device_private_split_cb(folio, new_folio);
>> +
>> expected_refs = folio_expected_ref_count(new_folio) + 1;
>> folio_ref_unfreeze(new_folio, expected_refs);
>>
>> - lru_add_split_folio(folio, new_folio, lruvec, list);
>> + if (!unmapped)
>> + lru_add_split_folio(folio, new_folio, lruvec,
>> list);
>>
>> /*
>> * Anonymous folio with swap cache.
>> @@ -3959,6 +3957,8 @@ static int __folio_split(struct folio *folio, unsigned
>> int new_order,
>> __filemap_remove_folio(new_folio, NULL);
>> folio_put_refs(new_folio, nr_pages);
>> }
>> +
>> + zone_device_private_split_cb(folio, NULL);
>> /*
>> * Unfreeze @folio only after all page cache entries, which
>> * used to point to it, have been updated with new folios.
>> @@ -3982,6 +3982,9 @@ static int __folio_split(struct folio *folio, unsigned
>> int new_order,
>>
>> local_irq_enable();
>>
>> + if (unmapped)
>> + return ret;
>
> As the comment of __folio_split() and __split_huge_page_to_list_to_order()
> mentioned:
>
> * The large folio must be locked
> * After splitting, the after-split folio containing @lock_at remains locked
>
> But here we seems to change the prerequisites.
>
> Hmm.. I am not sure this is correct.
>
The code is correct, but you are right in that the documentation needs to be
updated.
When "unmapped", we do want to leave the folios locked after the split.
Balbir
