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

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Date:   Wed, 27 Apr 2022 11:01:05 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Stephen Rothwell <sfr@...hwell.id.au>,
        Linux-MM <linux-mm@...ck.org>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Barry Song <21cnbao@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Page Reclaim v2 <page-reclaim@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
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        Shuang Zhai <szhai2@...rochester.edu>,
        Sofia Trinh <sofia.trinh@....works>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v10 07/14] mm: multi-gen LRU: exploit locality in rmap

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@...ux.ibm.com> wrote:
>>
>> Yu Zhao <yuzhao@...gle.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