On 2025/11/19 20:13, Lorenzo Stoakes wrote:
On Wed, Oct 22, 2025 at 12:37:16PM -0600, Nico Pache wrote:
From: Baolin Wang <[email protected]>
If any order (m)THP is enabled we should allow running khugepaged to
attempt scanning and collapsing mTHPs. In order for khugepaged to operate
when only mTHP sizes are specified in sysfs, we must modify the predicate
function that determines whether it ought to run to do so.
This function is currently called hugepage_pmd_enabled(), this patch
renames it to hugepage_enabled() and updates the logic to check to
determine whether any valid orders may exist which would justify
khugepaged running.
We must also update collapse_allowable_orders() to check all orders if
the vma is anonymous and the collapse is khugepaged.
After this patch khugepaged mTHP collapse is fully enabled.
Signed-off-by: Baolin Wang <[email protected]>
Signed-off-by: Nico Pache <[email protected]>
---
mm/khugepaged.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 54f5c7888e46..8ed9f8e2d376 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -418,23 +418,23 @@ static inline int collapse_test_exit_or_disable(struct
mm_struct *mm)
mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm);
}
-static bool hugepage_pmd_enabled(void)
+static bool hugepage_enabled(void)
{
/*
* We cover the anon, shmem and the file-backed case here; file-backed
* hugepages, when configured in, are determined by the global control.
- * Anon pmd-sized hugepages are determined by the pmd-size control.
+ * Anon hugepages are determined by its per-size mTHP control.
* Shmem pmd-sized hugepages are also determined by its pmd-size
control,
* except when the global shmem_huge is set to SHMEM_HUGE_DENY.
*/
if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
hugepage_global_enabled())
return true;
- if (test_bit(PMD_ORDER, &huge_anon_orders_always))
+ if (READ_ONCE(huge_anon_orders_always))
return true;
- if (test_bit(PMD_ORDER, &huge_anon_orders_madvise))
+ if (READ_ONCE(huge_anon_orders_madvise))
return true;
- if (test_bit(PMD_ORDER, &huge_anon_orders_inherit) &&
+ if (READ_ONCE(huge_anon_orders_inherit) &&
hugepage_global_enabled())
return true;
if (IS_ENABLED(CONFIG_SHMEM) && shmem_hpage_pmd_enabled())
@@ -508,7 +508,8 @@ static unsigned long collapse_allowable_orders(struct
vm_area_struct *vma,
vm_flags_t vm_flags, bool is_khugepaged)
{
enum tva_type tva_flags = is_khugepaged ? TVA_KHUGEPAGED :
TVA_FORCED_COLLAPSE;
- unsigned long orders = BIT(HPAGE_PMD_ORDER);
+ unsigned long orders = is_khugepaged && vma_is_anonymous(vma) ?
+ THP_ORDERS_ALL_ANON : BIT(HPAGE_PMD_ORDER);
Why are we doing this? If this is explicitly enabling mTHP for anon, which it
seems to be, can we please make this a little more explicit :)
I'd prefer this not to be a horribly squashed ternary, rather:
unsigned long orders;
/* We explicitly allow mTHP collapse for anonymous khugepaged ONLY. */
if (is_khugepaged && vma_is_anonymous(vma))
orders = THP_ORDERS_ALL_ANON;
else
orders = BIT(HPAGE_PMD_ORDER);
Yes, LGTM.
Also, does THP_ORDERS_ALL_ANON account for KHUGEPAGED_MIN_MTHP_ORDER? It's weird
to say that an order is allowed that isn't permitted by mTHP (e.g. order-0).
The THP_ORDERS_ALL_ANON has already filtered out order 0 and order 1, so
it matches the definition of KHUGEPAGED_MIN_MTHP_ORDER.
/*
* Mask of all large folio orders supported for anonymous THP; all
orders up to
* and including PMD_ORDER, except order-0 (which is not "huge") and
order-1
* (which is a limitation of the THP implementation).
*/
#define THP_ORDERS_ALL_ANON ((BIT(PMD_ORDER + 1) - 1) & ~(BIT(0) | BIT(1)))
