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mm/huge_memory: make min_order_for_split() always return an order

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min_order_for_split() returns -EBUSY when the folio is truncated and
cannot be split.  In commit 77008e1b2e ("mm/huge_memory: do not change
split_huge_page*() target order silently"), memory_failure() does not
handle it and pass -EBUSY to try_to_split_thp_page() directly. 
try_to_split_thp_page() returns -EINVAL since -EBUSY becomes 0xfffffff0 as
new_order is unsigned int in __folio_split() and this large new_order is
rejected as an invalid input.  The code does not cause a bug. 
soft_offline_in_use_page() also uses min_order_for_split() but it always
passes 0 as new_order for split.

Fix it by making min_order_for_split() always return an order.  When the
given folio is truncated, namely folio->mapping == NULL, return 0 and let
a subsequent split function handle the situation and return -EBUSY.

Add kernel-doc to min_order_for_split() to clarify its use.

Link: https://lkml.kernel.org/r/20251126210618.1971206-4-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zi Yan
2025-11-26 16:06:17 -05:00
committed by Andrew Morton
parent 5842bcbfc3
commit 2f78910659
2 changed files with 22 additions and 9 deletions
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25
mm/huge_memory.c
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@@ -4219,16 +4219,29 @@ int folio_split(struct folio *folio, unsigned int new_order,
SPLIT_TYPE_NON_UNIFORM);
}
int min_order_for_split(struct folio *folio)
/**
* min_order_for_split() - get the minimum order @folio can be split to
* @folio: folio to split
*
* min_order_for_split() tells the minimum order @folio can be split to.
* If a file-backed folio is truncated, 0 will be returned. Any subsequent
* split attempt should get -EBUSY from split checking code.
*
* Return: @folio's minimum order for split
*/
unsigned int min_order_for_split(struct folio *folio)
{
if (folio_test_anon(folio))
return 0;
if (!folio->mapping) {
if (folio_test_pmd_mappable(folio))
count_vm_event(THP_SPLIT_PAGE_FAILED);
return -EBUSY;
}
/*
* If the folio got truncated, we don't know the previous mapping and
* consequently the old min order. But it doesn't matter, as any split
* attempt will immediately fail with -EBUSY as the folio cannot get
* split until freed.
*/
if (!folio->mapping)
return 0;
return mapping_min_folio_order(folio->mapping);
}