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mm/huge_memory: merge uniform_split_supported() and non_uniform_split_supported() 

uniform_split_supported() and non_uniform_split_supported() share
significantly similar logic.

The only functional difference is that uniform_split_supported() includes
an additional check on the requested @new_order.

The reason for this check comes from the following two aspects:

  * some file system or swap cache just supports order-0 folio
  * the behavioral difference between uniform/non-uniform split

The behavioral difference between uniform split and non-uniform:

  * uniform split splits folio directly to @new_order
  * non-uniform split creates after-split folios with orders from
    folio_order(folio) - 1 to new_order.

This means for non-uniform split or !new_order split we should check the
file system and swap cache respectively.

This commit unifies the logic and merge the two functions into a single
combined helper, removing redundant code and simplifying the split
support checking mechanism.

Link: https://lkml.kernel.org/r/20251106034155.21398-3-richard.weiyang@gmail.com
Fixes: c010d47f10 ("mm: thp: split huge page to any lower order pages")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: "David Hildenbrand (Red Hat)" <david@kernel.org>
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: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Wei Yang 2025-11-06 03:41:55 +00:00 committed by Andrew Morton
parent c467061fbb
commit 8a0e4bdddd
2 changed files with 33 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/huge_mm.h
View File

@ -374,10 +374,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
unsigned int new_order, bool unmapped);
int min_order_for_split(struct folio *folio);
int split_folio_to_list(struct folio *folio, struct list_head *list);
bool uniform_split_supported(struct folio *folio, unsigned int new_order,
bool warns);
bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
bool warns);
bool folio_split_supported(struct folio *folio, unsigned int new_order,
enum split_type split_type, bool warns);
int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
struct list_head *list);
@ -408,7 +406,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
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))
if (!folio_split_supported(folio, new_order, SPLIT_TYPE_NON_UNIFORM, /* warns= */ false))
return split_huge_page_to_order(&folio->page, new_order);
return folio_split(folio, new_order, page, NULL);
}

71
mm/huge_memory.c
View File

@ -3593,8 +3593,8 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
return 0;
}
bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
bool warns)
bool folio_split_supported(struct folio *folio, unsigned int new_order,
enum split_type split_type, bool warns)
{
if (folio_test_anon(folio)) {
/* order-1 is not supported for anonymous THP. */
@ -3602,48 +3602,41 @@ bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
"Cannot split to order-1 folio");
if (new_order == 1)
return false;
} else if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
!mapping_large_folio_support(folio->mapping)) {
/*
* No split if the file system does not support large folio.
* Note that we might still have THPs in such mappings due to
* CONFIG_READ_ONLY_THP_FOR_FS. But in that case, the mapping
* does not actually support large folios properly.
*/
VM_WARN_ONCE(warns,
"Cannot split file folio to non-0 order");
return false;
}
/* Only swapping a whole PMD-mapped folio is supported */
if (folio_test_swapcache(folio)) {
VM_WARN_ONCE(warns,
"Cannot split swapcache folio to non-0 order");
return false;
}
return true;
}
/* See comments in non_uniform_split_supported() */
bool uniform_split_supported(struct folio *folio, unsigned int new_order,
bool warns)
{
if (folio_test_anon(folio)) {
VM_WARN_ONCE(warns && new_order == 1,
"Cannot split to order-1 folio");
if (new_order == 1)
return false;
} else if (new_order) {
} else if (split_type == SPLIT_TYPE_NON_UNIFORM || new_order) {
if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
!mapping_large_folio_support(folio->mapping)) {
/*
* We can always split a folio down to a single page
* (new_order == 0) uniformly.
*
* For any other scenario
* a) uniform split targeting a large folio
* (new_order > 0)
* b) any non-uniform split
* we must confirm that the file system supports large
* folios.
*
* Note that we might still have THPs in such
* mappings, which is created from khugepaged when
* CONFIG_READ_ONLY_THP_FOR_FS is enabled. But in that
* case, the mapping does not actually support large
* folios properly.
*/
VM_WARN_ONCE(warns,
"Cannot split file folio to non-0 order");
return false;
}
}
if (new_order && folio_test_swapcache(folio)) {
/*
* swapcache folio could only be split to order 0
*
* non-uniform split creates after-split folios with orders from
* folio_order(folio) - 1 to new_order, making it not suitable for any
* swapcache folio split. Only uniform split to order-0 can be used
* here.
*/
if ((split_type == SPLIT_TYPE_NON_UNIFORM || new_order) && folio_test_swapcache(folio)) {
VM_WARN_ONCE(warns,
"Cannot split swapcache folio to non-0 order");
return false;
@ -3711,11 +3704,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
if (new_order >= old_order)
return -EINVAL;
if (split_type == SPLIT_TYPE_UNIFORM && !uniform_split_supported(folio, new_order, true))
return -EINVAL;
if (split_type == SPLIT_TYPE_NON_UNIFORM &&
!non_uniform_split_supported(folio, new_order, true))
if (!folio_split_supported(folio, new_order, split_type, /* warn = */ true))
return -EINVAL;
is_hzp = is_huge_zero_folio(folio);