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[70.30.145.63]) by smtp.gmail.com with ESMTPSA id t66-20020a374645000000b007203bbbbb31sm1994600qka.47.2023.02.09.11.26.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Feb 2023 11:26:42 -0800 (PST) Date: Thu, 9 Feb 2023 14:26:40 -0500 From: Peter Xu To: Muhammad Usama Anjum Cc: David Hildenbrand , Andrew Morton , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Mike Rapoport , Nadav Amit , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com Subject: Re: [PATCH v10 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Message-ID: References: <20230202112915.867409-1-usama.anjum@collabora.com> <20230202112915.867409-6-usama.anjum@collabora.com> MIME-Version: 1.0 In-Reply-To: <20230202112915.867409-6-usama.anjum@collabora.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 54B461C001B X-Stat-Signature: kbxxpu6sxcx375qunt37mutri5fk3ana X-HE-Tag: 1675970806-993346 X-HE-Meta: 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 6l5BiTyR jEcLy+49sLJ03F/KtKMHfv3DwPoTi5vdP4jifp6nzXiiz7fVOZAXhEhfBviHMkpO//tEpAxOSCru1Kag8nfU3MLE0eTJiOQbIpCqMb1nLyL9mq8Kmw8XlsacY5EYovDEKO+wAVX3JnSBp7kiFD+xoDhYAs89fMsz+eeFtYBvuybzBDxZl1zO+Drswam13Btv4KF8wAySH56+OeS1oK58GCVX9CJxcCwdeqq+7rV8cwOSM3gB2aS2ZjpomvHpndoxKKMaGiDTmFIWG36YQ0u/3GEiXhnOC4tE1m/56Ud8k/50ah+B6KgzkFSxDBz/u4tjRpSVUyIGMkLbVfplvFietkFblibwcjMEQUiP25SKJVHZd4ACtx0BCuag10emfhp+3tPwShiLjvjKA+Devxw6Z0BhMn7G6WIVA1LK0lgJnuy/CWXBJoZqR503n5h86Va3VgdZ+rvzc/LrijSqpJNyyXhnqb3dLtYYe/vnlmahR/nNc3c0= 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: On Thu, Feb 02, 2023 at 04:29:14PM +0500, Muhammad Usama Anjum wrote: > Add some explanation and method to use write-protection and written-to > on memory range. > > Signed-off-by: Muhammad Usama Anjum > --- > Documentation/admin-guide/mm/pagemap.rst | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst > index 6e2e416af783..1cb2189e9a0d 100644 > --- a/Documentation/admin-guide/mm/pagemap.rst > +++ b/Documentation/admin-guide/mm/pagemap.rst > @@ -230,3 +230,27 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-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. > + > +Pagemap Scan IOCTL > +================== > + > +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get and/or clear > +the info about page table entries. The following operations are supported in > +this IOCTL: > +- Get the information if the pages have been written-to (``PAGE_IS_WRITTEN``), > + file mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``) or swapped > + (``PAGE_IS_SWAPPED``). > +- Write-protect the pages (``PAGEMAP_WP_ENGAGE``) to start finding which > + pages have been written-to. > +- Find pages which have been written-to and write protect the pages > + (atomic ``PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE``) Could we extend this section a bit more? Some points for reference: - The new struct you introduced, definitions of each of the fields, and generic use cases for each of the field/ops. - It'll be nice to list the OPs the new interface supports (GET, WP_ENGAGE, GET+WP_ENGAGE). - When should people use this rather than the old pagemap interface? What's the major problems to solve / what's the major difference? (Maybe nice to reference the Windows API too here) > + > +To get information about which pages have been written-to and/or write protect > +the pages, following must be performed first in order: > + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall. > + 2. The ``UFFD_FEATURE_WP_ASYNC`` feature is set by ``UFFDIO_API`` IOCTL. > + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode > + through ``UFFDIO_REGISTER`` IOCTL. > +Then the any part of the registered memory or the whole memory region can be > +write protected using the ``UFFDIO_WRITEPROTECT`` IOCTL or ``PAGEMAP_SCAN`` > +IOCTL. This part looks good. Thanks, -- Peter Xu