Re: [PATCH RFC 1/2] mm: collect the number of anon large folios

[David Hildenbrand <david@redhat.com>]

On 09.08.24 11:05, Ryan Roberts wrote:
> On 09/08/2024 09:58, David Hildenbrand wrote:
>> On 09.08.24 10:42, David Hildenbrand wrote:
>>>>> Not sure I fully understand why David prefers to do the unaccounting at
>>>>> free-time though? It feels unbalanced to me to increment when first mapped but
>>>>> decrement when freed. Surely its safer to either use alloc/free or use first
>>>>> map/last map?
>>>>>
>>>>> If using alloc/free isn't there a THP constructor/destructor that prepares the
>>>>> deferred list? (My memory may be failing me). Could we use that?
>>>>
>>>> Additionally, if we wanted to extend (eventually) to track the number of shmem
>>>> and file mthps in additional counters, could we also account using similar folio
>>>> free-time hooks? If not, it might be an argument to account in rmap_unmap to be
>>>> consistent for all?
>>>
>>> Again, see NR_FILE_THPS handling. No rmap over-complication please.
>>
>> ... not to mention that it is non-sensical to only count pageache folios that
>> are mapped to user space ;)
> 
> Yes, good point. I'll get back in my box. :)

Well, it was a valuable discussion!

anon folios in the swapcache are interesting: they are only "anon" after 
we first mapped them (harder to change, but would be possible by using a 
NULL mapping maybe, if really worth it; with memdesc that might turn out 
interesting). But once they are anon, they will stay anon until actually 
reclaimed -> freed.

-- 
Cheers,

David / dhildenb