On 6/10/26 7:33 PM, Lance Yang wrote:
On Wed, Jun 10, 2026 at 06:29:14PM +0800, Baolin Wang wrote:
We are now ready to enable shmem mTHP collapse, allowing
thp_vma_allowable_orders() to check all permissible shmem large orders.
Signed-off-by: Baolin Wang <[email protected]>
---
mm/khugepaged.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 75b18ec4a6c3..a87918b7e18c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -578,9 +578,14 @@ static unsigned long collapse_possible_orders(struct
vm_area_struct *vma,
{
unsigned long orders;
- /* If khugepaged is scanning an anonymous vma, allow mTHP collapse */
+ /*
+ * If khugepaged is scanning an anonymous or shmem vma,
+ * allow mTHP collapse.
+ */
if ((tva_flags == TVA_KHUGEPAGED) && vma_is_anonymous(vma))
orders = THP_ORDERS_ALL_ANON;
+ else if ((tva_flags == TVA_KHUGEPAGED) && vma_is_shmem(vma))
+ orders = THP_ORDERS_ALL_FILE_DEFAULT;
Hmm... for shmem, is the lower bound in mthp_collapse() expected?
#define KHUGEPAGED_MIN_MTHP_ORDER 2
#define THP_ORDERS_ALL_FILE_DEFAULT \
((BIT(MAX_PAGECACHE_ORDER + 1) - 1) & ~BIT(0))
KHUGEPAGED_MIN_MTHP_ORDER is 2, which was introduced for anon collapse.
For shmem, though, we're feeding mthp_collapse() orders from
THP_ORDERS_ALL_FILE_DEFAULT, and that only filter out order-0 ...
if (order > KHUGEPAGED_MIN_MTHP_ORDER &&
(enabled_orders & GENMASK(order - 1, 0))) {
order--;
continue;
}
So order-1 never gets a chance. The walker stops at order-2 and never
tries it, right?
Good suggestion. Originally, Nico used chunks (one chunk representing
the KHUGEPAGED_MIN_MTHP_ORDER range) to record the bitmap, which was
inconvenient for shmem to extend to order 1 collapse. Now that the
bitmap has been extended to MAX_PTRS_PER_PTE, that earlier limitation no
longer exists. I'll fix this.
Thanks for taking a look.
