The patch titled
Subject: mm/vma: do not register private-anon mappings with khugepaged during mmap
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-vma-do-not-register-private-anon-mappings-with-khugepaged-during-mmap.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vma-do-not-register-private-anon-mappings-with-khugepaged-during-mmap.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Dev Jain <dev.jain@xxxxxxx>
Subject: mm/vma: do not register private-anon mappings with khugepaged during mmap
Date: Thu, 6 Mar 2025 12:00:37 +0530
We already are registering private-anon VMAs with khugepaged during fault
time, in do_huge_pmd_anonymous_page(). Commit "register suitable readonly
file vmas for khugepaged" moved the khugepaged registration logic from
shmem_mmap to the generic mmap path.
The userspace-visible effect should be this: khugepaged will unnecessarily
scan mm's which haven't yet faulted in. Note that it won't actually
collapse because all PTEs are none.
Now that I think about it, the mm is going to have a file VMA anyways
during fork+exec, so the mm already gets registered during mmap due to the
non-anon case (I *think*), so at least one of either the mmap registration
or fault-time registration is redundant.
Make this logic specific for non-anon mappings.
Link: https://lkml.kernel.org/r/20250306063037.16299-1-dev.jain@xxxxxxx
Fixes: 613bec092fe7 ("mm: mmap: register suitable readonly file vmas for khugepaged")
Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Matthew Wilcow (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vma.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/vma.c~mm-vma-do-not-register-private-anon-mappings-with-khugepaged-during-mmap
+++ a/mm/vma.c
@@ -2381,7 +2381,8 @@ static int __mmap_new_vma(struct mmap_st
* vma_merge_new_range() calls khugepaged_enter_vma() too, the below
* call covers the non-merge case.
*/
- khugepaged_enter_vma(vma, map->flags);
+ if (!vma_is_anonymous(vma))
+ khugepaged_enter_vma(vma, map->flags);
ksm_add_vma(vma);
*vmap = vma;
return 0;
_
Patches currently in -mm which might be from dev.jain@xxxxxxx are
mm-vma-do-not-register-private-anon-mappings-with-khugepaged-during-mmap.patch
mm-remove-redundant-return-in-set_huge_zero_folio.patch
