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

[Pratyush Yadav <pratyush@kernel.org>]

On Tue, Aug 11 2026, Mike Rapoport wrote:

> 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.

Makes sense I think. We can review the patches here, but then they can
go in with the DMA series.

-- 
Regards,
Pratyush Yadav