Re: [PATCH] mm: synchronize with PTE table reclaim for all folio sizes

["David Hildenbrand (Arm)" <david@kernel.org>]

On 11/5/26 10:00, Baolin Wang wrote:
> CC Barry, who added the TTU_SYNC in shrink_folio_list().
> 
> On 11/5/26 1:48 PM, Lance Yang wrote:
>>
>>
>> On 2026/11/5 12:54, Lance Yang wrote:
>>>
>>>
>>> Good catch!
>>>
>>>
>>> Right. Whether the folio can be PMD-mapped doesn't tell us whether its
>>> PTE table can be reclaimed, so those extra checks can skip synchronization
>>> that the caller explicitly asked for ;)
>>
>> Ouch ... one thing I missed ... what about order-0 reclaim?
>>
>> shrink_folio_list() only sets TTU_SYNC for large folio, so can't we still
>> hit the same race there?
> 
> Thanks Lance. But this matches the purpose of the TTU_SYNC flag, which is used
> to avoid racy checks with PVMW_SYNC. If no TTU_SYNC flag is set, it means the
> caller can tolerate some racy checks.
> 
> For this case, I think we should set TTU_SYNC unconditionally in
> shrink_folio_list(). Barry, what do you think?

That makes sense. I hope this doesn't throw a big wrench into our reclaim
performance numbers.

Can someone benchmark this?

But maybe we should really follow-up with the folio-size based optimization in
sync_with_folio_pmd_zap(), where we only need a memory barrier (and sufficient
documentation why something that cannot be PMD-mapped can get away cheaper).

-- 
Cheers,

David