mm/huge_memory: add split_huge_page_to_order()

Patch series "Optimize folio split in memory failure", v5.

This patchset optimizes folio split operations in memory failure code by
always splitting a folio to min_order_for_split() to minimize unusable
pages, even if min_order_for_split() is non zero and memory failure code
would take the failed path eventually for a successfully split folio. 

This means instead of making the entire original folio unusable memory
failure code would only make its after-split folio, which has order of
min_order_for_split() and contains HWPoison page, unusable.

For soft offline case, since the original folio is still accessible, no
split is performed if the folio cannot be split to order-0 to prevent
potential performance loss.

In addition, add split_huge_page_to_order() to improve code readability
and fix kernel-doc comment format for folio_split() and other related
functions.

Background
==========

This patchset is a follow-up of "[PATCH v3] mm/huge_memory: do not change
split_huge_page*() target order silently."[1] and [PATCH v4]
mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0
order[2], since both are separated out as hotfixes.  It improves how
memory failure code handles large block size(LBS) folios with
min_order_for_split() > 0.  By splitting a large folio containing HW
poisoned pages to min_order_for_split(), the after-split folios without HW
poisoned pages could be freed for reuse.  To achieve this, folio split
code needs to set has_hwpoisoned on after-split folios containing HW
poisoned pages and it is done in the hotfix in [2].

This patchset includes:
1. A patch adds split_huge_page_to_order(),
2. Patch 2 and Patch 3 of "[PATCH v2 0/3] Do not change split folio target
   order"[3],


This patch (of 3):

When the caller does not supply a list to
split_huge_page_to_list_to_order(), use split_huge_page_to_order()
instead.

Link: https://lkml.kernel.org/r/20251031162001.670503-1-ziy@nvidia.com
Link: https://lkml.kernel.org/r/20251031162001.670503-2-ziy@nvidia.com
Link: https://lore.kernel.org/all/20251017013630.139907-1-ziy@nvidia.com/ [1]
Link: https://lore.kernel.org/all/20251023030521.473097-1-ziy@nvidia.com/ [2]
Link: https://lore.kernel.org/all/20251016033452.125479-1-ziy@nvidia.com/ [3]
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Luis Chamberalin <mcgrof@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Pankaj Raghav <kernel@pankajraghav.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 396d9e3d1d46..a06924cf4065 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -381,6 +381,10 @@ static inline int split_huge_page_to_list_to_order(struct page *page, struct lis
 {
 	return __split_huge_page_to_list_to_order(page, list, new_order, false);
 }
+static inline int split_huge_page_to_order(struct page *page, unsigned int new_order)
+{
+	return split_huge_page_to_list_to_order(page, NULL, new_order);
+}
 
 /*
  * try_folio_split_to_order - try to split a @folio at @page to @new_order using
@@ -400,8 +404,7 @@ static inline int try_folio_split_to_order(struct folio *folio,
 		struct page *page, unsigned int new_order)
 {
 	if (!non_uniform_split_supported(folio, new_order, /* warns= */ false))
-		return split_huge_page_to_list_to_order(&folio->page, NULL,
-				new_order);
+		return split_huge_page_to_order(&folio->page, new_order);
 	return folio_split(folio, new_order, page, NULL);
 }
 static inline int split_huge_page(struct page *page)
@@ -587,6 +590,11 @@ split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 	VM_WARN_ON_ONCE_PAGE(1, page);
 	return -EINVAL;
 }
+static inline int split_huge_page_to_order(struct page *page, unsigned int new_order)
+{
+	VM_WARN_ON_ONCE_PAGE(1, page);
+	return -EINVAL;
+}
 static inline int split_huge_page(struct page *page)
 {
 	VM_WARN_ON_ONCE_PAGE(1, page);