On Tue, Jun 4, 2024 at 5:47 PM <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.
>
> 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;
> + }
Am I missing something? if file system doesn't support large folio,
how could the large folio start to exist from the first place while its
mapping points to a file which doesn't support large folio?
> }
> }
>
> -
> is_hzp = is_huge_zero_folio(folio);
> if (is_hzp) {
> pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
> --
> 2.15.2
>
Thanks
Barry
