+ mm-huge_memory-disallow-hugepages-if-the-system-wide-thp-sysfs-settings-are-disabled.patch added to mm-new branch

+ mm-huge_memory-disallow-hugepages-if-the-system-wide-thp-sysfs-settings-are-disabled.patch added to mm-new branch

[Andrew Morton]

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The patch titled
     Subject: mm: huge_memory: disallow hugepages if the system-wide THP sysfs settings are disabled
has been added to the -mm mm-new branch.  Its filename is
     mm-huge_memory-disallow-hugepages-if-the-system-wide-thp-sysfs-settings-are-disabled.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-disallow-hugepages-if-the-system-wide-thp-sysfs-settings-are-disabled.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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------------------------------------------------------
From: Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: mm: huge_memory: disallow hugepages if the system-wide THP sysfs settings are disabled
Date: Thu, 5 Jun 2025 16:00:58 +0800

Patch series "fix MADV_COLLAPSE issue if THP settings are disabled", v2.

As we discussed in the previous thread [1], the MADV_COLLAPSE will ignore
the system-wide anon/shmem THP sysfs settings, which means that even
though we have disabled the anon/shmem THP configuration, MADV_COLLAPSE
will still attempt to collapse into a anon/shmem THP.  This violates the
rule we have agreed upon: never means never.  This patch set will address
this issue.


This patch (of 2):

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.

Another rule for madvise, referring to David's suggestion: “allowing for
collapsing in a VM without VM_HUGEPAGE in the "madvise" mode would be
fine".

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.

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 that orders are prohibited from being used,
   then madvise_collapse() is forbidden for that orders.

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 that orders are still
   prohibited from being used, thus madvise_collapse() is not allowed for
   that orders.

Link: https://lkml.kernel.org/r/8eefb0809c598fadaa4a022634fba5689a4f3257.1749109709.git.baolin.wang@linux.alibaba.com
Link: https://lore.kernel.org/all/1f00fdc3-a3a3-464b-8565-4c1b23d34f8d@linux.alibaba.com/ [1]
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/huge_mm.h |   23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

--- a/include/linux/huge_mm.h~mm-huge_memory-disallow-hugepages-if-the-system-wide-thp-sysfs-settings-are-disabled
+++ a/include/linux/huge_mm.h
@@ -287,20 +287,35 @@ unsigned long thp_vma_allowable_orders(s
 				       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)))
+			return 0;
+
+		if (!(tva_flags & TVA_ENFORCE_SYSFS))
+			goto skip;
+
+		mask = always;
 		if (vm_flags & VM_HUGEPAGE)
-			mask |= READ_ONCE(huge_anon_orders_madvise);
+			mask |= madvise;
 		if (hugepage_global_always() ||
 		    ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()))
-			mask |= READ_ONCE(huge_anon_orders_inherit);
+			mask |= inherit;
 
 		orders &= mask;
 		if (!orders)
 			return 0;
 	}
 
+skip:
 	return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
 }
 
_

Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are

mm-fix-the-inaccurate-memory-statistics-issue-for-users.patch
mm-huge_memory-disallow-hugepages-if-the-system-wide-thp-sysfs-settings-are-disabled.patch
mm-shmem-disallow-hugepages-if-the-system-wide-shmem-thp-sysfs-settings-are-disabled.patch