On 14/08/2025 04:07, Yafang Shao wrote:

On Wed, Aug 13, 2025 at 9:57 PM Usama Arif [off-list ref] wrote:

quoted

From: David Hildenbrand <redacted>

When determining which THP orders are eligible for a VMA mapping,
we have previously specified tva_flags, however it turns out it is
really not necessary to treat these as flags.

Rather, we distinguish between distinct modes.

The only case where we previously combined flags was with
TVA_ENFORCE_SYSFS, but we can avoid this by observing that this
is the default, except for MADV_COLLAPSE or an edge cases in
collapse_pte_mapped_thp() and hugepage_vma_revalidate(), and
adding a mode specifically for this case - TVA_FORCED_COLLAPSE.

We have:
* smaps handling for showing "THPeligible"
* Pagefault handling
* khugepaged handling
* Forced collapse handling: primarily MADV_COLLAPSE, but also for
  an edge case in collapse_pte_mapped_thp()

Disregarding the edge cases, we only want to ignore sysfs settings only
when we are forcing a collapse through MADV_COLLAPSE, otherwise we
want to enforce it, hence this patch does the following flag to enum
conversions:

* TVA_SMAPS | TVA_ENFORCE_SYSFS -> TVA_SMAPS
* TVA_IN_PF | TVA_ENFORCE_SYSFS -> TVA_PAGEFAULT
* TVA_ENFORCE_SYSFS             -> TVA_KHUGEPAGED
* 0                             -> TVA_FORCED_COLLAPSE

With this change, we immediately know if we are in the forced collapse
case, which will be valuable next.

Signed-off-by: David Hildenbrand <redacted>
Acked-by: Usama Arif <redacted>
Signed-off-by: Usama Arif <redacted>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lorenzo Stoakes <redacted>

Acked-by: Yafang Shao <redacted>

Hello Usama,

This change is also required by my BPF-based THP order selection
series [0]. Since this patch appears to be independent of the series,
could we merge it first into mm-new or mm-everything if the series
itself won't be merged shortly?

Link: https://lwn.net/Articles/1031829/ [0]

Thanks for reviewing!

All of the patches in the series have several acks/reviews. Only a small change
might be required in selftest, so hopefully the next revision is the last one.

Andrew - would it be ok to start including this entire series in the mm-new now?

Thanks!