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

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Date:   Tue, 26 Apr 2022 22:38:17 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.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>,
        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

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.

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