[PATCH v10 07/14] mm: multi-gen LRU: exploit locality in rmap

[Aneesh Kumar K V]

On 4/27/22 10:08 AM, Yu Zhao wrote:
> On Tue, Apr 26, 2022 at 10:33 PM Aneesh Kumar K.V
> <aneesh.kumar at linux.ibm.com> wrote:
>>
>> Yu Zhao <yuzhao at google.com> writes:
>>
>> ....
>>
>>   diff --git a/mm/rmap.c b/mm/rmap.c
>>> index fedb82371efe..7cb7ef29088a 100644
>>> --- a/mm/rmap.c
>>> +++ b/mm/rmap.c
>>> @@ -73,6 +73,7 @@
>>>   #include <linux/page_idle.h>
>>>   #include <linux/memremap.h>
>>>   #include <linux/userfaultfd_k.h>
>>> +#include <linux/mm_inline.h>
>>>
>>>   #include <asm/tlbflush.h>
>>>
>>> @@ -821,6 +822,12 @@ static bool folio_referenced_one(struct folio *folio,
>>>                }
>>>
>>>                if (pvmw.pte) {
>>> +                     if (lru_gen_enabled() && pte_young(*pvmw.pte) &&
>>> +                         !(vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))) {
>>> +                             lru_gen_look_around(&pvmw);
>>> +                             referenced++;
>>> +                     }
>>
>> Is it required to update referenced here? we do that below after
>> clearing the young bit. Or is the goal to identify whether we found any
>> young pte around?
> 
> referenced++ is needed because lru_gen_look_around() also clears the
> young bit in pvmw.pte. And ptep_clear_flush_young_notify() will return
> false unless mmu notifier returns true.

should we then use a mmu notifier variant of clear_young in 
lru_gen_look_around() ?

-aneesh