Re: [PATCHv7 13/18] mm: Drop fake head checks

[David Hildenbrand (Arm)]

On 10/27/26 14:13, Muchun Song wrote:
> 
> 
>> On Oct 27, 2026, at 20:31, Kiryl Shutsemau <kas@xxxxxxxxxx> wrote:
>>
>> On Tue, Oct 27, 2026 at 01:05:58PM +0100, David Hildenbrand (Arm) wrote:
>>>
>>> Right. Without HVO we would just corrupt pages in the single folio (which is
>>> also not nice).
>>>
>>> I'm also questioning whether we need this RO protection all the time active.
>>
>> What do you have in mind? RO only under a debug option, or switching the
>> tail page to RO some time after the remap?
> 
> I don't think enabling RO only on debug kernels is a good choice.
> 
> Within ByteDance, we once successfully caught memory failures using RO (because
> we backported HVO, but some missing commits in memory failure caused write
> operations on tail pages to persist). These operations triggered invalid writes
> to shared tail pages.

But would you have caught it with debug setting on in initial rollout / experiments?

> 
> Under the old HVO schema, this invalid write only corrupted one folio, but under
> the new schema, it corrupts all HVOed folios. Therefore, I personally believe
> that for the new schema, the value of RO is even greater.
But doesn't that mean that you would find serious bugs faster one way or the other?

Silent corruption of any folio state is not good.

-- 
Cheers,

David