Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue

[David Hildenbrand (Arm)]

On 3/15/26 01:23, Andrew Morton wrote:
> On Sat, 14 Mar 2026 17:05:54 -0700 SeongJae Park <sj@xxxxxxxxxx> wrote:
> 
>>  Because THPs are
>> removed from the deferred_list, THP shinker cannot split the underutilized THPs
>> in time.  As a result, users will show less free memory than before.
> 
> That'll do, thanks ;)
> 
> Pasted, added cc:stable.  It's been there since 6.12 so I don't see a
> need to rush this in, so I won't move this into mm-hotfixes - it'll go
> into mainline for 7.1-rc1 after which -stable should pick it up.

Makes sense. I guess using the partially-mapped is only a slight
problem, because we usually try to split partially-mapped before migrating.

So it's mostly about over-allocated THPs (mostly 0) not getting scanned
and split+reclaimed after they were migrated.

Under memory pressure without swap, that might create a user-visible
problem, especially when many such THPs are migrated before being
scanned for zeropages that can be reclaimed.

-- 
Cheers,

David