On 2025/5/29 23:10, Zi Yan wrote:
On 29 May 2025, at 4:23, Baolin Wang wrote:
The MADV_COLLAPSE will ignore the system-wide Anon THP sysfs settings, which
means that even though we have disabled the Anon THP configuration, MADV_COLLAPSE
will still attempt to collapse into a Anon THP. This violates the rule we have
agreed upon: never means never.
To address this issue, should check whether the Anon THP configuration is disabled
in thp_vma_allowable_orders(), even when the TVA_ENFORCE_SYSFS flag is set.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
include/linux/huge_mm.h | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2f190c90192d..199ddc9f04a1 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -287,20 +287,35 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
unsigned long orders)
{
/* Optimization to check if required orders are enabled early. */
- if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
- unsigned long mask = READ_ONCE(huge_anon_orders_always);
+ if (vma_is_anonymous(vma)) {
+ unsigned long always = READ_ONCE(huge_anon_orders_always);
+ unsigned long madvise = READ_ONCE(huge_anon_orders_madvise);
+ unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);
+ unsigned long mask = always | madvise;
+
+ /*
+ * If the system-wide THP/mTHP sysfs settings are disabled,
+ * then we should never allow hugepages.
+ */
+ if (!(mask & orders) && !(hugepage_global_enabled() && (inherit & orders)))
Can you explain the logic here? Is it equivalent to:
1. if THP is set to always, always_mask & orders == 0, or
2. if THP if set to madvise, madvise_mask & order == 0, or
3. if THP is set to inherit, inherit_mask & order == 0?
I cannot figure out why (always | madvise) & orders does not check
THP enablement case, but inherit & orders checks hugepage_global_enabled().
Sorry for not being clear. Let me try again:
Now we can control per-sized mTHP through ‘huge_anon_orders_always’, so
always does not need to rely on the check of hugepage_global_enabled().
For madvise, referring to David's suggestion: “allowing for collapsing
in a VM without VM_HUGEPAGE in the "madvise" mode would be fine", so we
can just check 'huge_anon_orders_madvise' without relying on
hugepage_global_enabled().
In the case where hugepage_global_enabled() is enabled, we need to check
whether the 'inherit' has enabled the corresponding orders.
In summary, the current strategy is:
1. If always & orders == 0, and madvise & orders == 0, and
hugepage_global_enabled() == false (global THP settings are not
enabled), it means mTHP of the orders are prohibited from being used,
then madvise_collapse() is forbidden.
2. If always & orders == 0, and madvise & orders == 0, and
hugepage_global_enabled() == true (global THP settings are enabled), and
inherit & orders == 0, it means mTHP of the orders are still prohibited
from being used, and thus madvise_collapse() is not allowed.
