Re: [PATCH mm-new v3] mm: mincore: use per-vma lock during page table walk

["David Hildenbrand (Arm)" <david@kernel.org>]

On 9/16/26 06:31, Kefeng Wang wrote:
> do_mincore() performs a read-only, per-VMA residency query,
> making it a good candidate for per-VMA locking. Convert it
> to acquire the per-VMA lock, thereby reducing contention on
> the per-MM mmap_lock.
> 
> Reviewed-by: Pedro Falcato <pfalcato@suse.de>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> v3:
> - add vma_assert_locked, update changelog/comment, per David

It likely was Lorenzo :)

> - Add RB 
> v2, (RESEND):
> - using new vma_start_read_unlocked() API, suggestted by Pedro Falcato
> v1:
> - https://lore.kernel.org/linux-mm/20260701144047.3786939-2-wangkefeng.wang@huawei.com/
> 
>  mm/mincore.c | 29 +++++++++++++++++------------
>  1 file changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/mincore.c b/mm/mincore.c
> index c086836bc4bc..0fe50f8a7e62 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -235,24 +235,22 @@ static const struct mm_walk_ops mincore_walk_ops = {
>  	.pmd_entry		= mincore_pte_range,
>  	.pte_hole		= mincore_unmapped_range,
>  	.hugetlb_entry		= mincore_hugetlb,
> -	.walk_lock		= PGWALK_RDLOCK,
> +	.walk_lock		= PGWALK_VMA_RDLOCK_VERIFY,
>  };
>  
>  /*
>   * Do a chunk of "sys_mincore()". We've already checked
> - * all the arguments, we hold the mmap semaphore: we should
> + * all the arguments, we hold the VMA read lock: we should
>   * just return the amount of info we're asked for.
>   */
> -static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
> +static long do_mincore(struct vm_area_struct *vma, unsigned long addr,
> +		unsigned long pages, unsigned char *vec)
>  {
> -	struct vm_area_struct *vma;
> -	unsigned long end;
> +	unsigned long end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
>  	int err;
>  
> -	vma = vma_lookup(current->mm, addr);
> -	if (!vma)
> -		return -ENOMEM;
> -	end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
> +	vma_assert_locked(vma);

I think Lorenzo asked whether we should do that. But the walk_page_vma() further
below would already verify that due to PGWALK_VMA_RDLOCK_VERIFY (see
process_vma_walk_lock) so not sure if that's really required here.

AFAIKS, everything we do in mincore_pte_range() should be compatible with the
VMA lock, including the swap and pagecache handling.

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

-- 
Cheers,

David