Re: [PATCH v5 7/8] mm: thp: split huge page to any lower order pages

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Hi Andrew,

On 26 Feb 2024, at 15:55, Zi Yan wrote:

> From: Zi Yan <ziy@xxxxxxxxxx>
> To split a THP to any lower order pages, we need to reform THPs on
> subpages at given order and add page refcount based on the new page
> order. Also we need to reinitialize page_deferred_list after removing
> the page from the split_queue, otherwise a subsequent split will
> see list corruption when checking the page_deferred_list again.
> Note: Anonymous order-1 folio is not supported because _deferred_list,
> which is used by partially mapped folios, is stored in subpage 2 and an
> order-1 folio only has subpage 0 and 1. File-backed order-1 folios are
> fine, since they do not use _deferred_list.
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
>  include/linux/huge_mm.h |  21 +++++---
>  mm/huge_memory.c        | 110 +++++++++++++++++++++++++++++++---------
>  2 files changed, 99 insertions(+), 32 deletions(-)

Can you fold the fixup below into this patch (per discussion with Ryan at [1])? Thanks.

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 50d146eb248f..fd745bcc97ff 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3059,11 +3059,8 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,

        if (new_order) {
                /* Only swapping a whole PMD-mapped folio is supported */
-               if (folio_test_swapcache(folio)) {
-                       VM_WARN_ONCE(1,
-                               "Cannot split swap-cached folio to non-0 order");
+               if (folio_test_swapcache(folio))
                        return -EINVAL;
-               }
                /* Split shmem folio to non-zero order not supported */
                if (shmem_mapping(folio->mapping)) {


Best Regards,
Yan, Zi

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