Re: [PATCH] mm/thp: expose deferred split folio memory usage in meminfo

[Ye Liu]

在 2026/7/17 16:37, David Hildenbrand (Arm) 写道:
> On 7/17/26 08:30, Ye Liu wrote:
>> From: Ye Liu <liuye@xxxxxxxxxx>
>>
>> Folios on the deferred split list hold physical memory that is
>> invisible in meminfo. When a THP becomes partially mapped, the
>> unmapped pages are removed from AnonPages but remain physically
>> allocated until the shrinker splits the folio. This creates a
>> memory accounting gap where used memory cannot be attributed to
>> any meminfo field.
>>
>> Add NR_DEFERRED_SPLIT_PAGES to track the total memory consumed by
>> folios currently on the deferred_split_lru, updated via
>> mod_node_page_state() at all enqueue/dequeue points. The new field
>> DeferredSplitPages is visible in /proc/meminfo, /proc/vmstat, and
>> per-node /sys/devices/system/node/node*/meminfo.
>>
> 
> Oh no.
> 
> This is really exposing a current implementation detail where we have this
> information easily available in a way that we will not be able to change that
> implementation later.
> 

Yes, `/proc/meminfo` is a user-space ABI.                                
Adding it there means you can't change the semantics,                    
and the field will become unmaintainable, yet you can't delete it either.
But I think this information is still necessary.                         
Where would be a better place to put it?                                 

-- 
Thanks,
Ye Liu