linux-kernel - Re: [PATCH v11 07/14] mm: multi-gen LRU: exploit locality in rmap

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Message-ID: <CAHk-=wirMfOpzNavjWao5GA65ve=9LQN-6=YCUtJGRpu=ujdoA@mail.gmail.com>
Date:   Wed, 8 Jun 2022 08:51:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Barry Song <21cnbao@...il.com>
Cc:     Yu Zhao <yuzhao@...gle.com>, Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>, Andi Kleen <ak@...ux.intel.com>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        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>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Kernel Page Reclaim v2 <page-reclaim@...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>, huzhanyuan@...o.com
Subject: Re: [PATCH v11 07/14] mm: multi-gen LRU: exploit locality in rmap

On Tue, Jun 7, 2022 at 5:43 PM Barry Song <21cnbao@...il.com> wrote:
>
> Given we used to have a flush for clear pte young in LRU, right now we are
> moving to nop in almost all cases for the flush unless the address becomes
> young exactly after look_around and before ptep_clear_flush_young_notify.
> It means we are actually dropping flush. So the question is,  were we
> overcautious? we actually don't need the flush at all even without mglru?

We stopped flushing the TLB on A bit clears on x86 back in 2014.

See commit b13b1d2d8692 ("x86/mm: In the PTE swapout page reclaim case
clear the accessed bit instead of flushing the TLB").

               Linus