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

Shakeel Butt
2026-04-24T17:03:33Z

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.
>
> Before commit 4d5d14a01e2c ("mm/mglru: rework workingset
> protection"), folios with PG_active were always placed in
> the youngest generation, leading to over-protection and
> increased refaults. After that commit, PG_active folios
> are placed in the second youngest generation, which is
> still too optimistic given the presence of readahead. In
> contrast, the classic active/inactive scheme is more
> conservative.
>
> This patch switches to folio_mark_accessed(). If
> folio_check_references() later detects referenced PTEs,
> the folio will be promoted based on the reference flag
> set by folio_mark_accessed().
>

There is a following comment and stat update in lru_gen_refault() which is
referring to setting active bit which this patch is removing.

/* see folio_add_lru() where folio_set_active() will be called */
if (lru_gen_in_fault())
mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);

Is this still relevant or need changes?

I have not yet dig deeper into the patch and the heuristic. Will do later.