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

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

On 7/15/26 3:57 PM, Barry Song wrote:
> On Wed, Jul 15, 2026 at 3:54 PM Barry Song <baohua@kernel.org> wrote:
> [...]
>>>>
>>>> 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. :-)
> 
> Second thought: we don't do much readahead for VM_EXEC since it is
> considered random access. So maybe I am being over-cautious here.
> The data will tell us :-)

Yes. Besides, even if an exec folio gets promoted incorrectly at first, 
it can still be reclaimed as it ages without further accesses. This is 
the same logic as the classical LRU.

I did a quick test with the same test case on my x86 machine, and I 
still see an improvement in sys time.

base			patched
1152.249s		993.235s