On 04.06.24 07:47, xu.xin16@xxxxxxxxxx wrote:
From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
When I did a large folios split test, a WARNING
"[ 5059.122759][ T166] Cannot split file folio to non-0 order"
was triggered. But my test cases are only for anonmous folios.
while mapping_large_folio_support() is only reasonable for page
cache folios.
Agreed.
I wonder if mapping_large_folio_support() should either
a) Complain if used for anon folios, so we can detect the wrong use more
easily. (VM_WARN_ON_ONCE())
b) Return "true" for anonymous mappings, although that's more debatable.
In split_huge_page_to_list_to_order(), the folio passed to
mapping_large_folio_support() maybe anonmous folio. The
folio_test_anon() check is missing. So the split of the anonmous THP
is failed. This is also the same for shmem_mapping(). We'd better add
a check for both. But the shmem_mapping() in __split_huge_page() is
not involved, as for anonmous folios, the end parameter is set to -1, so
(head[i].index >= end) is always false. shmem_mapping() is not called.
Using /sys/kernel/debug/split_huge_pages to verify this, with this
patch, large anon THP is successfully split and the warning is ceased.
Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
Cc: xu xin <xu.xin16@xxxxxxxxxx>
Cc: Yang Yang <yang.yang29@xxxxxxxxxx>
---
mm/huge_memory.c | 38 ++++++++++++++++++++------------------
1 file changed, 20 insertions(+), 18 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 317de2afd371..4c9c7e5ea20c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3009,31 +3009,33 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
if (new_order >= folio_order(folio))
return -EINVAL;
- /* Cannot split anonymous THP to order-1 */
- if (new_order == 1 && folio_test_anon(folio)) {
- VM_WARN_ONCE(1, "Cannot split to order-1 folio");
- return -EINVAL;
- }
-
if (new_order) {
/* Only swapping a whole PMD-mapped folio is supported */
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,
- "Cannot split shmem folio to non-0 order");
- return -EINVAL;
- }
- /* No split if the file system does not support large folio */
- if (!mapping_large_folio_support(folio->mapping)) {
- VM_WARN_ONCE(1,
- "Cannot split file folio to non-0 order");
- return -EINVAL;
+
+ if (folio_test_anon(folio)) {
+ /* Cannot split anonymous THP to order-1 */
+ if (new_order == 1) {
+ VM_WARN_ONCE(1, "Cannot split to order-1 folio");
+ return -EINVAL;
+ }
+ } else {
+ /* Split shmem folio to non-zero order not supported */
+ if (shmem_mapping(folio->mapping)) {
+ VM_WARN_ONCE(1,
+ "Cannot split shmem folio to non-0 order");
+ return -EINVAL;
+ }
+ /* No split if the file system does not support large folio */
+ if (!mapping_large_folio_support(folio->mapping)) {
+ VM_WARN_ONCE(1,
+ "Cannot split file folio to non-0 order");
+ return -EINVAL;
+ }
}
}
What about the following sequence:
if (folio_test_anon(folio)) {
if (new_order == 1)
...
} else if (new_order) {
if (shmem_mapping(...))
...
...
}
if (folio_test_swapcache(folio) && new_order)
return -EINVAL;
Should result in less churn and reduce indentation level.
--
Cheers,
David / dhildenb
