On 21/07/2026 17:12, David Hildenbrand (Arm) wrote:
On 7/14/26 16:04, Kevin Brodsky wrote:
quoted
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
This isn't mainly about the overhead, but rather the fact that from here
on the ctor/dtor do nothing for kernel page tables. Patch 20-22 rely on
this, and in part 2 I would go further and only ever call the ctor/dtor
for user page tables, so that the mm_is_kernel() check can be dropped.
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Thanks for the reviews!
- Kevin