Re: [PATCH v8 11/15] khugepaged: allow madvise_collapse to check all anonymous mTHP orders

[Baolin Wang]

On 2025/7/2 13:57, Nico Pache wrote:
> Allow madvise_collapse to scan/collapse all mTHP orders without the
> strict requirement of needing the PMD-order enabled.
>
> Signed-off-by: Nico Pache <npache@xxxxxxxxxx>

I am afraid we should drop this patch from the series, since Hugh 
explicitly opposed my modification of the madvise_collapse control logic 
in this thread[1].

Moreover, since we have not yet clarified how to handle the conflict 
between the semantics of madvise_collapse and the THP interfaces, we 
should keep the current logic[2] (means madvise_collapse still only 
allows PMD collapse).

If madvise_collapse is to support mTHP collapse, there will be more 
semantic conflicts to discuss.

[1] 
https://lore.kernel.org/all/cover.1750815384.git.baolin.wang@xxxxxxxxxxxxxxxxx/
[2] 
https://lore.kernel.org/all/23b8ad10-cd1f-45df-a25c-78d01c8af44f@xxxxxxxxxx/

> ---
>   mm/khugepaged.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b96a7327b9c0..6ea681b81647 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2930,11 +2930,13 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>   	unsigned long hstart, hend, addr;
>   	int thps = 0, last_fail = SCAN_FAIL;
>   	bool mmap_locked = true;
> +	unsigned long orders = vma_is_anonymous(vma) ?
> +					THP_ORDERS_ALL_ANON : BIT(PMD_ORDER);
>   
>   	BUG_ON(vma->vm_start > start);
>   	BUG_ON(vma->vm_end < end);
>   
> -	if (!thp_vma_allowable_order(vma, vma->vm_flags, 0, PMD_ORDER))
> +	if (!thp_vma_allowable_orders(vma, vma->vm_flags, 0, orders))
>   		return -EINVAL;
>   
>   	cc = kmalloc(sizeof(*cc), GFP_KERNEL);
> @@ -2956,7 +2958,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>   			mmap_read_lock(mm);
>   			mmap_locked = true;
>   			result = hugepage_vma_revalidate(mm, addr, false, &vma,
> -							 cc, BIT(HPAGE_PMD_ORDER));
> +							 cc, orders);
>   			if (result  != SCAN_SUCCEED) {
>   				last_fail = result;
>   				goto out_nolock;