+Luis and Pankaj, who are working on enable bs > ps in XFS and touch split_huge_page_to_list_to_order().
On 4 Jun 2024, at 6:52, Zi Yan wrote:
> On 4 Jun 2024, at 0:57, David Hildenbrand wrote:
>
>> On 04.06.24 07:47, xu.xin16@xxxxxxxxxx wrote:
>>> From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
>>>
>>> When I did a large folios split test, a WARNING
>>> "[ 5059.122759][ T166] Cannot split file folio to non-0 order"
>>> was triggered. But my test cases are only for anonmous folios.
>>> while mapping_large_folio_support() is only reasonable for page
>>> cache folios.
>>
>> Agreed.
>>
>> I wonder if mapping_large_folio_support() should either
>>
>> a) Complain if used for anon folios, so we can detect the wrong use more easily. (VM_WARN_ON_ONCE())
>
> This is much better.
>
>>
>> b) Return "true" for anonymous mappings, although that's more debatable.
>
> This might fix the warning here, but the function might get wrong uses easily.
>
>>
>>>
>>> In split_huge_page_to_list_to_order(), the folio passed to
>>> mapping_large_folio_support() maybe anonmous folio. The
>>> folio_test_anon() check is missing. So the split of the anonmous THP
>>> is failed. This is also the same for shmem_mapping(). We'd better add
>>> a check for both. But the shmem_mapping() in __split_huge_page() is
>>> not involved, as for anonmous folios, the end parameter is set to -1, so
>>> (head[i].index >= end) is always false. shmem_mapping() is not called.
>>>
>>> Using /sys/kernel/debug/split_huge_pages to verify this, with this
>>> patch, large anon THP is successfully split and the warning is ceased.
>>>
>>> Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
>>> Cc: xu xin <xu.xin16@xxxxxxxxxx>
>>> Cc: Yang Yang <yang.yang29@xxxxxxxxxx>
>>> ---
>>> mm/huge_memory.c | 38 ++++++++++++++++++++------------------
>>> 1 file changed, 20 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 317de2afd371..4c9c7e5ea20c 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -3009,31 +3009,33 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>>> if (new_order >= folio_order(folio))
>>> return -EINVAL;
>>>
>>> - /* Cannot split anonymous THP to order-1 */
>>> - if (new_order == 1 && folio_test_anon(folio)) {
>>> - VM_WARN_ONCE(1, "Cannot split to order-1 folio");
>>> - return -EINVAL;
>>> - }
>>> -
>>> if (new_order) {
>>> /* Only swapping a whole PMD-mapped folio is supported */
>>> if (folio_test_swapcache(folio))
>>> return -EINVAL;
>>> - /* Split shmem folio to non-zero order not supported */
>>> - if (shmem_mapping(folio->mapping)) {
>>> - VM_WARN_ONCE(1,
>>> - "Cannot split shmem folio to non-0 order");
>>> - return -EINVAL;
>>> - }
>>> - /* No split if the file system does not support large folio */
>>> - if (!mapping_large_folio_support(folio->mapping)) {
>>> - VM_WARN_ONCE(1,
>>> - "Cannot split file folio to non-0 order");
>>> - return -EINVAL;
>>> +
>>> + if (folio_test_anon(folio)) {
>>> + /* Cannot split anonymous THP to order-1 */
>>> + if (new_order == 1) {
>>> + VM_WARN_ONCE(1, "Cannot split to order-1 folio");
>>> + return -EINVAL;
>>> + }
>>> + } else {
>>> + /* Split shmem folio to non-zero order not supported */
>>> + if (shmem_mapping(folio->mapping)) {
>>> + VM_WARN_ONCE(1,
>>> + "Cannot split shmem folio to non-0 order");
>>> + return -EINVAL;
>>> + }
>>> + /* No split if the file system does not support large folio */
>>> + if (!mapping_large_folio_support(folio->mapping)) {
>>> + VM_WARN_ONCE(1,
>>> + "Cannot split file folio to non-0 order");
>>> + return -EINVAL;
>>> + }
>>> }
>>> }
>>
>> What about the following sequence:
>>
>> if (folio_test_anon(folio)) {
>> if (new_order == 1)
>> ...
>> } else if (new_order) {
>> if (shmem_mapping(...))
>> ...
>> ...
>> }
>>
>> if (folio_test_swapcache(folio) && new_order)
>> return -EINVAL;
>>
>> Should result in less churn and reduce indentation level.
>
> Yeah, this looks better to me.
>
> Best Regards,
> Yan, Zi
Best Regards,
Yan, Zi
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