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Thu, 12 Aug 2021 15:59:07 +0000 From: Tiberiu A Georgescu To: corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org Cc: peter.xu@redhat.com, ivan.teterevkov@nutanix.com, florian.schmidt@nutanix.com, carl.waldspurger@nutanix.com, jonathan.davies@nutanix.com, Tiberiu A Georgescu Subject: [PATCH] Documentation: update pagemap with SOFT_DIRTY & UFFD_WP shmem issue Date: Thu, 12 Aug 2021 15:58:43 +0000 Message-Id: <20210812155843.236919-1-tiberiu.georgescu@nutanix.com> X-Mailer: git-send-email 2.32.0.380.geb27b338a3 Content-Type: text/plain X-ClientProxiedBy: SJ0PR13CA0129.namprd13.prod.outlook.com (2603:10b6:a03:2c6::14) To DM6PR02MB5578.namprd02.prod.outlook.com (2603:10b6:5:79::13) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from tiberiu-georgescu.ubvm.nutanix.com (192.146.154.243) by SJ0PR13CA0129.namprd13.prod.outlook.com (2603:10b6:a03:2c6::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4436.8 via Frontend Transport; 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dkim=pass header.d=nutanix.com header.s=proofpoint20171006 header.b=GnH2QCym; spf=none (imf05.hostedemail.com: domain of tiberiu.georgescu@nutanix.com has no SPF policy when checking 148.163.151.68) smtp.mailfrom=tiberiu.georgescu@nutanix.com; dmarc=pass (policy=none) header.from=nutanix.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8597D50445F6 X-Stat-Signature: m3133eknzdqmhnrxcmko7eybe5jcwuaq X-HE-Tag: 1628783950-608879 Content-Transfer-Encoding: quoted-printable 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: Mentioning the current missing functionality of the pagemap, in case someone stumbles upon unexpected behaviour. Signed-off-by: Tiberiu A Georgescu Reviewed-by: Ivan Teterevkov Reviewed-by: Florian Schmidt Reviewed-by: Carl Waldspurger Reviewed-by: Jonathan Davies --- Documentation/admin-guide/mm/pagemap.rst | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/adm= in-guide/mm/pagemap.rst index fb578fbbb76c..627f3832b3a2 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -207,3 +207,9 @@ Before Linux 3.11 pagemap bits 55-60 were used for "p= age-shift" (which is always 12 at most architectures). Since Linux 3.11 their meaning changes after first clear of soft-dirty bits. Since Linux 4.2 they are used for flags unconditionally. + +Note that the page table entries for swappable and non-syncable pages ar= e +cleared when those pages are zapped or swapped out. This makes informati= on +about the page disappear from the pagemap. The location of the swapped +page can still be retrieved from the page cache, but flags like SOFT_DIR= TY +and UFFD_WP are lost irretrievably. --=20 2.32.0.380.geb27b338a3