Re: [PATCH v7 2/3] kho: fix deferred init of kho scratch

[Pratyush Yadav <pratyush@kernel.org>]

On Tue, Apr 07 2026, Zi Yan wrote:

> On 7 Apr 2026, at 8:21, Pratyush Yadav wrote:
[...]
>> Hmm, I don't like that how complex this is. It adds another layer of
>> complexity to the initialization of the migratetype, and you have to dig
>> through all the possible call sites to be sure that we catch all the
>> cases. Makes it harder to wrap your head around it. Plus, makes it more
>> likely for bugs to slip through if later refactors change some page init
>> flow.
>>
>> Is the cost to look through the scratch array really that bad? I would
>> suspect we'd have at most 4-6 per-node scratches, and one global one
>> lowmem. So I'd expect around 10 items to look through, and it will
>> probably be in the cache anyway.
>
> It is not only about the cost of going through the scratch array, but also
> about adding kho code to the generic init_pageblock_migratetype().
> This means all callers of init_pageblock_migratetype(), no matter if
> they are involved with kho or not, need to do the check. It is a good
> practice to do the check when necessary, otherwise, this catch-all check
> might hide some bugs in the future.

We can move the check to memmap init, so it will still be done for most
pageblocks I reckon. The only other callers I see are zone device and
CMA.

Anyway, I get your point and am fine with moving it out to memmap init
functions.

[...]

-- 
Regards,
Pratyush Yadav