Re: [PATCH v2 1/3] mm/page_alloc: Optimize free_contig_range()

[Zi Yan]

On 20 Mar 2026, at 4:20, Vlastimil Babka (SUSE) wrote:

> On 3/19/26 23:07, David Hildenbrand (Arm) wrote:
>>>> the allocation of non-compound order>0, like you suggested in 3, we basically
>>>
>>> I suggested we'd take it away in the sense of not producing order>0 where
>>> head is refcounted, tails are not, and it's not a compound page. I'd rather
>>> have an API that applies split_page() before and returns it as order-0
>>> refcounted pages, but not the intermediate order>0 non-compound anymore.
>>
>> Are you talking about external API or internal API?
>
> In this case of alloc+split, external, and that would make sense to me.
>
> In case of freeing, the current free_pages(order>0) is also external and I
> would prefer not to augment it for this free_contig_range() usecase.
>
>> Regarding external interface: I think the crucial part is that an
>> external interface (free_contig_range) should always get a range of
>> individual order-0 pages: neither compound nor non-compound order > 0.
>
> Ack.
>
>> The individual order-0 pages can either be frozen or refcounted
>> (depending on the interface).
>
> Ack.
>
>> Regarding internal interface: To me that implies that FPI_PREPARED will
>> never ever have to do any kind of "subpage" (page) free_pages_prepare()
>> checks. It must already have been performed on all order-0 pages.
>>
>> So the TODO should indeed be dropped.
>
> Agreed. But maybe I misunderstood Zi, so that's why I tried to add so much
> detail about what I mean by what.

Ack on dropping the TODO.

I was discussing about whether we can have a better interface for freeing these
contiguous pages instead of FPI_PREPARED. Since FPI_PREPARED adds another
form of free pages, where free_pages_prepare() are called on all incoming
pages already. It might be a separate topic. I will think about it more
and come back later. Sorry for the confusion.

>
>> I'm not sure I understood whether you think using the
>> __free_frozen_pages() with order > 0 is okay, or whether we need a
>> different (internal) interface.
>
> I think this is fine. But I agree with you above that this assumes
> FPI_PREPARED and will not have to deal with subpages.


Best Regards,
Yan, Zi