Re: [PATCH] mm/mglru: Use folio_mark_accessed to replace folio_set_active in PF

[Barry Song]

On Fri, Apr 24, 2026 at 11:19 PM Pedro Falcato <pfalcato@xxxxxxx> wrote:
>
> On Sat, Apr 18, 2026 at 08:02:33PM +0800, Barry Song (Xiaomi) wrote:
> > MGLRU gives high priority to folios mapped in page tables.
> > As a result, folio_set_active() is invoked for all folios
> > read during page faults. In practice, however, readahead
> > can bring in many folios that are never accessed via page
> > tables.
> >
> > A previous attempt by Lei Liu proposed introducing a separate
> > LRU for readahead[1] to make readahead pages easier to reclaim,
> > but that approach is likely over-engineered.
>
> Why does this even need to be kept? I'm not sure it makes sense
> to even mark readahead folios as referenced.
>
> I'd suggest folios should only be marked referenced (or even active, whatever)
> when they're mapped. Anything else is a bit random and is hoping you are
> eventually going to map them in the future (which is not true for, for example,
> anything in an ELF file that may be readahead but not mapped, like debug info,
> symbol tables, section headers, relocation tables, etc etc)

The patch targets the mmap readahead path rather than the syscall
readahead path.

With lru_gen_in_fault() in place, it’s roughly equivalent to
the mapped case, since readahead is typically 128 KB while
fault_around is 64 KB in PF.

Thanks
Barry