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

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Date:   Wed, 27 Apr 2022 10:02:56 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Yu Zhao <yuzhao@...gle.com>, Stephen Rothwell <sfr@...hwell.id.au>,
        linux-mm@...ck.org
Cc:     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-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, page-reclaim@...gle.com,
        x86@...nel.org, Yu Zhao <yuzhao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Steven Barrett <steven@...uorix.net>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Daniel Byrne <djbyrne@....edu>,
        Donald Carr <d@...os-reins.com>,
        Holger Hoffstätte 
        <holger@...lied-asynchrony.com>,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>,
        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

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? 

> +
>  			if (ptep_clear_flush_young_notify(vma, address,
>  						pvmw.pte)) {
>  				/*