Re: [PATCH v4 2/2] kho: Introduce preserve/restore APIs for high-order pages

[Pratyush Yadav <pratyush@kernel.org>]

On Mon, Aug 03 2026, Pranjal Shrivastava wrote:

> The current KHO page preservation APIs (e.g. kho_preserve_pages) assume
> that multi-page blocks are split into independent 4KB pages during
> restoration. This is incompatible with high-order non-compound pages,
> such as DMA buffers, which must be restored with tail pages having a
> zero reference count.
>
> Introduce explicit preserve and restore APIs for high-order pages,
> which preserve and restore a high-order page block as a single unit,
> applying a refcount of 1 to the head page while leaving tail pages at 0.
> Rename the existing internal helper to __kho_restore_page() and
> consolidate the common restoration code into it.
>
> Signed-off-by: Pranjal Shrivastava <praan@google.com>

The code here looks very convoluted TBH. I think it will be simpler to
make kho_restore_page() only return non-compound pages. That is, it
returns 0 or higher order non-compound page.

Then kho_restore_pages() can call kho_restore_page() and then do
split_page() on the page it got to turn it into 0-order pages.
kho_restore_folio() can call kho_restore_page() and then do
prep_compound_page() on the page it got.

And then you expose kho_restore_page() to be used by DMA APIs to get
non-compound high order pages directly.

How does that sound?

[...]

-- 
Regards,
Pratyush Yadav