Re: [PATCH v4 0/2] kho: support preserving high-order non-compound pages

[Mike Rapoport <rppt@kernel.org>]

Hi Pranjal,

On Mon, Aug 03, 2026 at 11:39:41AM +0000, Pranjal Shrivastava wrote:
> Introduction
> ============
> This series is required for the ongoing effort to preserve DMA allocations
> across KHO [1]. It addresses a fundamental mismatch between the current KHO
> restoration logic and the physical reality of high-order buddy allocations.

I skimmed through the patches, they look fine to me before the in-depth
review :)

But we are really close to the merge window, so we'll anyway need to
reiterate after v7.3-rc1.
 
> The Problem
> ===========
> The current KHO restore implementation treats all multi-page blocks as
> split pages during restoration. Specifically, kho_restore_pages()
> initializes every 4KB sub-page with a refcount of 1.
> 
> However, many kernel subsystems, most notably the DMA allocator (via
> dma_alloc_coherent), frequently return high-order non-compound pages.
> In this state, only the head page carries a refcount of 1, while
> all tail pages have a refcount of 0.

This hints that these patches could be a part of the DMA preservation
series, unless you expect other users of the new API.

Generally, we don't merge new APIs without the users and if DMA
preservation is the only user, it's better to fold these two patches there.

-- 
Sincerely yours,
Mike.