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

[Pratyush Yadav]

On Wed, Aug 12 2026, Pranjal Shrivastava wrote:

> On Wed, Aug 12, 2026 at 12:32:25PM +0200, Pratyush Yadav wrote:
>> 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.
>> 
>
> So.. IIUC, I'll post a v5 here as a standalone series till we get
> consensus, and finally the reviewed patches can be folded with the DMA
> series?

That sounds good to me at least.

-- 
Regards,
Pratyush Yadav