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Subject: Re: [PATCH v2 0/2] mm: Remember a/d bits for migration entries
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <20220804203952.53665-1-peterx@redhat.com>
Date:   Thu, 4 Aug 2022 15:17:44 -0700
Cc:     Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Huang Ying <ying.huang@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Hugh Dickins <hughd@google.com>,
        Andi Kleen <andi.kleen@intel.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>
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Message-Id: <8FBBFD68-3315-48D6-B318-4AA5A170C0C8@gmail.com>
References: <20220804203952.53665-1-peterx@redhat.com>
To:     Peter Xu <peterx@redhat.com>
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On Aug 4, 2022, at 1:39 PM, Peter Xu <peterx@redhat.com> wrote:

>  (1) Page Idle Tracking
> 
>  Before this series, idle tracking can cause false negative if an accessed
>  page got migrated, since after migration the young bit will get lost.
>  After this series, it'll be better in that after migration young bit will
>  be persisted, so it'll be able to be detected correctly by page idle
>  logic when walking the pgtable.
> 
>  However there's still nothing done when page idle reset was carried out
>  during migration procedure in progress, but that should be a separate
>  topic to be addressed (e.g. to teach rmap pgtable walk code to be able to
>  walk with both present ptes and migration ptes).

IIUC, when a migration entry is set page_remove_rmap() is called by
try_to_migrate_one(), so improving page-idle accuracy should be done in a
different way.