Re: [PATCH 3/6] mm/mglru: enhance cold/hot inversion handling in inc_min_seq()

[Barry Song]

On Thu, Aug 27, 2026 at 8:46 AM Baoquan He <baoquan.he@xxxxxxxxx> wrote:
>
> On 08/27/26 at 05:43am, Barry Song wrote:
> > On Wed, Aug 26, 2026 at 4:56 PM Baoquan He <baoquan.he@xxxxxxxxx> wrote:
> > >
> > > On 08/21/26 at 06:25pm, Barry Song (Xiaomi) wrote:
> > > > During aging, a folio's generation may already have been updated by
> > > > folio_update_gen(), even though it has not yet been moved to the
> > > > corresponding generation list. Such folios are hotter than those
> > > > already in that generation.
> > > >
> > > > It makes sense for inc_min_seq() to increment the generation of
> > > > folios that were never promoted during aging and move them to the
> > > > tail of the new oldest generation. However, folios that were already
> > > > promoted should instead be moved to the head of their updated
> > > > generation, just as sort_folio() does in scan_folios().
> > >
> > > While sort_folio() move protected folio to the head of next gen too.
> > > It only moves ineligible folios to the tail of next gen.
> > >
> >
> > Hi Baoquan,
> >
> > Thanks for the review! I’m not quite sure I understand what you mean :-)
> > Could you please clarify what you’re suggesting?
>
> Sorry for the confusion, Barry. I meant this is a good one, and
> sort_folio() has the similar issue in which the protected folios are
> moved to the head, wondering if that need be adjusted too. One consistent
> rule for both is better.

I think it might be fine for sort_folio() to move protected folios to the
head, since those folios have either been accessed multiple times or have
reached a tier higher than tier_idx. They are sort of hot in theory, right?

if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1)

But for inc_min_seq(), it is just catching up to make sure the newest
generation doesn't overlap with the oldest generation. Those non-promoted
folios themselves aren't hot , so I feel these are actually different?

Best Regards
Barry