Re: [PATCH v4 5/7] mm/khugepaged: Refactor the PTE state checks into a helper

[Pedro Falcato]

On Tue, Aug 11, 2026 at 06:48:37AM -0600, Nico Pache (Red Hat) wrote:
> For anonymous collapse, the collapse_scan_pmd() and
> __collapse_huge_page_isolate() functions share a large portion of their
> logic. These functions both check the state of the PTEs and verify the
> following:
> 	- max_pte_* values are not exceeded
> 	- uffd is not active
> 	- lazyfree properties
> 	- non-anonymous
> 
> Merge these checks into a helper collapse_check_pte() to reduce code
> duplication. We also add a helper struct for this function called
> pte_check_context which allows us to pass the required parameters in a
> clean and elegant manner.
> 
> A helper function is also introduced pte_check_fail() to provide a clean
> interface to set the pte_check_context failure results and return
> PTE_CHECK_FAIL state. This helps reduce code duplications across the new
> collapse_check_pte function.
> 
> Two slight modifications are done to the original functionality. We now
> warn (instead of crash) if the anon test fails, and we leverage the
> vm_normal_folio function instead of page->folio, this should be
> functionally equivalent.
> 
> No other functional changes intended.
> 
> This patch is heavily based off work done by Lance Yang, but modified to
> deal with conflicts and feedback received during the review cycle [1].
> 
> [1] https://lore.kernel.org/linux-mm/20251008043748.45554-1-lance.yang@xxxxxxxxx/
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Nico Pache (Red Hat) <nico.pache@xxxxxxxxx>
> ---
>  mm/khugepaged.c | 298 +++++++++++++++++++++++++++++---------------------------
>  1 file changed, 157 insertions(+), 141 deletions(-)

Ugh, this is quite a big change, can you break it down into a bunch of
patches? It's quite hard to properly review otherwise.

The spirit of the change looks good itself, but the devil is always in the
details :)

-- 
Pedro