Re: [PATCH 15/22] mm: only initialise pt_share_count for user pgtables

From
David Hildenbrand (Arm) <david@kernel.org>
Date
2026-07-21 15:12:27
Also in
linux-arch, linux-efi, linux-mm, linux-riscv, linux-s390, linux-um, lkml, loongarch, sparclinux
Reply to
Kevin Brodsky, 2026-07-14
On 7/14/26 16:04, Kevin Brodsky wrote:
quoted hunk ↗ jump to hunk
ptdesc_pmd_pts_init() initialises the pt_share_count ptdesc field.
That field is only used for hugetlb tracking purposes, so there is
no need to initialise it for kernel page tables. Skip the call for
kernel page tables, like pmd_ptlock_init().

From now on pagetable_*_ctor() and pagetable_dtor() do nothing for
kernel page tables.

Signed-off-by: Kevin Brodsky <redacted>
---
 include/linux/mm.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 94f0fb1c662a..b217ccbed5a3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3905,9 +3905,12 @@ static inline spinlock_t *pmd_lock(struct mm_struct *mm, pmd_t *pmd)
 static inline bool pagetable_pmd_ctor(struct mm_struct *mm,
 				      struct ptdesc *ptdesc)
 {
-	if (!mm_is_kernel(mm) && !pmd_ptlock_init(ptdesc))
-		return false;
-	ptdesc_pmd_pts_init(ptdesc);
+	if (!mm_is_kernel(mm)) {
+		if (!pmd_ptlock_init(ptdesc))
+			return false;
+		ptdesc_pmd_pts_init(ptdesc);
+	}
+
I'd have said "the initialization is cheap, why bother", but we already do have
the mm_is_kernel() check in place, so

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David
Thread (51 messages) 51 messages, 7 authors, last reply 2026-08-11
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