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

[David Hildenbrand]

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