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

Zi Yan
2024-02-28T15:52:33Z

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Hi Andrew,

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

> From: Zi Yan <ziy@nvidia.com>
>
> 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@nvidia.com>
> ---
> 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)) {
VM_WARN_ONCE(1,

[1] https://lore.kernel.org/linux-mm/408df79a-130e-43cd-a21a-9b3a2ddef617@arm.com/

--
Best Regards,
Yan, Zi

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