linuxkpi: Add `split_page()`

[dumbbell]

Summary

This function is supposed to split large pages into an array of PAGE_SIZE-sized pages, with correct refcounting. This is apparently used to allow some drivers to free a part of a large page only.

I don't think we use large pages in linuxkpi. Therefore, this new function is curently a no-op.

The DRM drivers TTM memory manager started to use it in Linux 6.15.

Sponsored by: The FreeBSD Foundation

[emaste]

I don't think we use large pages in linuxkpi. Therefore, this new function is curently a no-op.

Is there a way we can add either a compile-time error or KASSERT to ensure this remains the case?

[bz]

In D58762#1348310, @emaste wrote:

I don't think we use large pages in linuxkpi. Therefore, this new function is curently a no-op.

Is there a way we can add either a compile-time error or KASSERT to ensure this remains the case?

Or at least at the pr_debug("%s:TODO\n", func). I really should make that a macro and replace all occurrences.

[dumbbell]

Add a TODO.

I did’t find an API to get the size of a page, so I’m not sure how to implement an assertion.

[bz]

You'll likely have to make ttm_pool_split_for_swap() return early then in FreeBSD?