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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 8 Jun 2022 08:51:40 -0700
Message-ID: <CAHk-=wirMfOpzNavjWao5GA65ve=9LQN-6=YCUtJGRpu=ujdoA@mail.gmail.com>
Subject: Re: [PATCH v11 07/14] mm: multi-gen LRU: exploit locality in rmap
To:     Barry Song <21cnbao@gmail.com>
Cc:     Yu Zhao <yuzhao@google.com>, Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>, Andi Kleen <ak@linux.intel.com>,
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On Tue, Jun 7, 2022 at 5:43 PM Barry Song <21cnbao@gmail.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