Re: [PATCH] mm: mglru: promote mapped executable folios after first usage

[Barry Song]

On Wed, Jul 15, 2026 at 2:58 PM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> On 7/15/26 2:52 PM, Barry Song wrote:
> > On Wed, Jul 15, 2026 at 2:33 PM Baolin Wang
> > <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> >>
> >> Classical LRU protects mapped executable file folios through commit
> >> 8cab4754d24a0 ("vmscan: make mapped executable pages the first class
> >> citizen") and commit c909e99364c8 ("vmscan: activate executable pages
> >> after first usage"), giving executable code a better chance to stay in
> >> memory, avoiding IO thrashing and improving workload performance.
> >>
> >> However, MGLRU's protection of mapped executable file folios is less
> >> reliable. Although shrink_folio_list() checks references, the access flag
> >> of mapped executable file folios may have already been checked and
> >> cleared by lru_gen_look_around() or walk_mm(). Additionally,
> >> folio_update_gen() only sets the 'PG_referenced' flag for mapped executable
> >> file folios, which causes shrink_folio_list() to ignore the first usage
> >> of these mapped executable file folios and reclaim them.
> >>
> >> Follow the classical LRU's logic, promoting mapped executable file folios
> >> after their first usage in folio_update_gen(), giving executable code a
> >> better chance to stay in memory.
> >>
> >> On my 32-core Arm machine, with the memcg limit set to 2G, running
> >> 'make -j32' to build kernel showed some improvement in sys time.
> >
> > Hi Baolin,
> >
> > Because ARM doesn't set the surrounding PTEs to young, while x86
> > may behave differently and mark the surrounding PTEs as young as
> > well. Could we also collect the data on x86?
> >
> > void set_pte_range(struct vm_fault *vmf, struct folio *folio,
> >                  struct page *page, unsigned int nr, unsigned long addr)
> > {
> >          ...
> >
> >          if (prefault && arch_wants_old_prefaulted_pte())
> >                  entry = pte_mkold(entry);
> >          else
> >                  entry = pte_sw_mkyoung(entry);
>
> Sure. But I don't think it's very relevant to this point. MGLRU doesn't
> protect normally accessed mmaped exec file folios well enough. Anyway,
> I'll test it on x86.

My point is that even mmaped executable folios that have never been
accessed might still get promoted because they already have the accessed
bit set. :-)