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Mon, 15 Mar 2021 00:27:37 +0000 Received: from MN2PR12MB3823.namprd12.prod.outlook.com ([fe80::a1b1:5d8:47d7:4b60]) by MN2PR12MB3823.namprd12.prod.outlook.com ([fe80::a1b1:5d8:47d7:4b60%7]) with mapi id 15.20.3933.032; Mon, 15 Mar 2021 00:27:36 +0000 From: "Zi Yan" To: "Yu Zhao" , "Matthew Wilcox" Cc: linux-mm@kvack.org, "Alex Shi" , "Andrew Morton" , "Dave Hansen" , "Hillf Danton" , "Johannes Weiner" , "Joonsoo Kim" , "Mel Gorman" , "Michal Hocko" , "Roman Gushchin" , "Vlastimil Babka" , "Wei Yang" , "Yang Shi" , "Ying Huang" , linux-kernel@vger.kernel.org, page-reclaim@google.com Subject: Re: [PATCH v1 06/14] mm, x86: support the access bit on non-leaf PMD entries Date: Sun, 14 Mar 2021 20:27:29 -0400 X-Mailer: MailMate (1.14r5757) Message-ID: <3465DA3A-B735-4657-A1E0-89CF5DE0D4FF@nvidia.com> In-Reply-To: References: <20210313075747.3781593-1-yuzhao@google.com> <20210313075747.3781593-7-yuzhao@google.com> <74C83FFE-DC78-40CD-B6BE-00614DC8F125@nvidia.com> <20210314225103.GQ2577561@casper.infradead.org> Content-Type: multipart/signed; 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identity=mailfrom; envelope-from=""; helo=NAM04-CO1-obe.outbound.protection.outlook.com; client-ip=40.107.69.57 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615768059-960530 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: --=_MailMate_CBFB7DBC-C603-4F2A-AF6A-DDA4A1BE8835_= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On 14 Mar 2021, at 20:03, Yu Zhao wrote: > On Sun, Mar 14, 2021 at 10:51:03PM +0000, Matthew Wilcox wrote: >> On Sun, Mar 14, 2021 at 06:12:42PM -0400, Zi Yan wrote: >>> 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 ar= e >>>> interested in the accessed bit on children can take advantage of thi= s: >>>> 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 accesse= d >>>> 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? >> >> The first few sentences from 4.8: >> >> : For any paging-structure entry that is used during linear-address >> : translation, bit 5 is the accessed flag. For paging-structure >> : entries that map a page (as opposed to referencing another paging >> : structure), bit 6 is the dirty flag. These flags are provided for >> : use by memory-management software to manage the transfer of pages an= d >> : paging structures into and out of physical memory. >> >> : Whenever the processor uses a paging-structure entry as part of >> : linear-address translation, it sets the accessed flag in that entry >> : (if it is not already set). Matthew, thanks for the pointer. > > As far as I know x86 is the one that supports this. > >> The way they differentiate between the A and D bits makes it clear to >> me that the A bit is set at each level of the tree, but the D bit is >> only set on leaf entries. > > And the difference makes perfect sense (to me). Kudos to Intel. Hi Yu, You only introduced HAVE_ARCH_PARENT_PMD_YOUNG but no HAVE_ARCH_PARENT_PU= D_YOUNG. Is it PUD granularity too large to be useful for multigenerational LRU al= gorithm? Thanks. =E2=80=94 Best Regards, Yan Zi --=_MailMate_CBFB7DBC-C603-4F2A-AF6A-DDA4A1BE8835_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQJDBAEBCgAtFiEEh7yFAW3gwjwQ4C9anbJR82th+ooFAmBOqfEPHHppeUBudmlk aWEuY29tAAoJEJ2yUfNrYfqK7ioP/iXqhqf8coxd9BziPjMq8dDbSltEG7lgcfrS uJ/Qu4Q+nu6iY4H36HgkGcjcnf6QbWtzu9CJBi2zUuWYoT4mgR9mFA6E1sHE7EBk hTufjKU4ondt5J1EMXjdh1az0Hn4OSgU0xMzW1dNzFutOhNi+AZpr5uB7IgwPcTa UOq3c624FcJvCOtQTX92kh1xrYQfzqIdZmAw4q/IjFH93C6OPJxVK2f6fwS9g+Cd DK9sPSZHbchFhBMZM6JDdDveAwCpCHHGzP1bRQlQSe5zGO+kvBO57lj968LnJeEQ kWrqdXvl/wUcXZyc95D3Kob+TCoYkbIyps9t41E7GIWN4DZzv3J1e+yEgvpu/rOr gvcVlqgxUmG5ONlrqMDcX+FyAFYuRCLXStM8OVVaLtiyi/qpR3cjxud1lEPvEtgw 3ivGxUTIIVuOohf60wRsXbFYMzZQYAgYs/dJYxSBXnpkDaccpmvuKwmGjkJz1lzH Ig8P7Wew0Bpr+Xz1Hr7Bd3KYoLsKRE475tF5Kbk8gvN0esGc8JpvWQ450Aox24kK w8Gq0ESCjHUJrR3LzbKUTr+5for2gz6lPxeWciaiVFCVwxG1wNbaOhSu4GEDxgos yBD6YqVwMWcVmmH+ir8Mc3ocx8Z6HIw76RPFw4oxw0ULH21P327si7cuyk0wP8sL H3zpnVI7 =dIvm -----END PGP SIGNATURE----- --=_MailMate_CBFB7DBC-C603-4F2A-AF6A-DDA4A1BE8835_=--