linux-kernel - Re: [PATCH v1 06/14] mm, x86: support the access bit on non-leaf PMD entries

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Message-ID: <74C83FFE-DC78-40CD-B6BE-00614DC8F125@nvidia.com>
Date:   Sun, 14 Mar 2021 18:12:42 -0400
From:   "Zi Yan" <ziy@...dia.com>
To:     "Yu Zhao" <yuzhao@...gle.com>
Cc:     linux-mm@...ck.org, "Alex Shi" <alex.shi@...ux.alibaba.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Hillf Danton" <hdanton@...a.com>,
        "Johannes Weiner" <hannes@...xchg.org>,
        "Joonsoo Kim" <iamjoonsoo.kim@....com>,
        "Matthew Wilcox" <willy@...radead.org>,
        "Mel Gorman" <mgorman@...e.de>, "Michal Hocko" <mhocko@...e.com>,
        "Roman Gushchin" <guro@...com>, "Vlastimil Babka" <vbabka@...e.cz>,
        "Wei Yang" <richard.weiyang@...ux.alibaba.com>,
        "Yang Shi" <shy828301@...il.com>,
        "Ying Huang" <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
        page-reclaim@...gle.com
Subject: Re: [PATCH v1 06/14] mm, x86: support the access bit on non-leaf PMD
 entries

On 13 Mar 2021, at 2:57, Yu Zhao wrote:

> Some architectures support the accessed bit on non-leaf PMD entries
> (parents) in addition to leaf PTE entries (children) where pages are
> mapped, e.g., x86_64 sets the accessed bit on a parent when using it
> as part of linear-address translation [1]. Page table walkers who are
> interested in the accessed bit on children can take advantage of this:
> they do not need to search the children when the accessed bit is not
> set on a parent, given that they have previously cleared the accessed
> bit on this parent in addition to its children.
>
> [1]: Intel 64 and IA-32 Architectures Software Developer's Manual
>      Volume 3 (October 2019), section 4.8

Just curious. Does this also apply to non-leaf PUD entries? Do you
mind sharing which sentence from the manual gives the information?

Thanks.

—
Best Regards,
Yan Zi

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