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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 7/15/26 2:52 PM, Barry Song wrote:
> On Wed, Jul 15, 2026 at 2:33 PM Baolin Wang
> <baolin.wang@linux.alibaba.com> 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.