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(p200300cbc7092700cdd8dcb02a698783.dip0.t-ipconnect.de. [2003:cb:c709:2700:cdd8:dcb0:2a69:8783]) by smtp.gmail.com with ESMTPSA id n13sm15598929wrv.94.2022.01.26.05.55.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Jan 2022 05:55:11 -0800 (PST) Message-ID: <2190b8e2-74f2-0e31-0a40-0401fbd9966e@redhat.com> Date: Wed, 26 Jan 2022 14:55:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [RFC PATCH 0/6] Add support for shared PTEs across processes To: Matthew Wilcox Cc: "Kirill A. Shutemov" , Khalid Aziz , akpm@linux-foundation.org, longpeng2@huawei.com, arnd@arndb.de, dave.hansen@linux.intel.com, rppt@kernel.org, surenb@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Xu References: <20220125114212.ks2qtncaahi6foan@box.shutemov.name> <20220125135917.ezi6itozrchsdcxg@box.shutemov.name> <20220125185705.wf7p2l77vggipfry@box.shutemov.name> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E944318003B X-Rspam-User: nil Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=WXjqVzF4; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf24.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Stat-Signature: 4hdkgfmqtgz1mzs76n1zh9wtd65e95ue X-Rspamd-Server: rspam08 X-HE-Tag: 1643205316-644146 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000640, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 26.01.22 14:38, Matthew Wilcox wrote: > On Wed, Jan 26, 2022 at 11:16:42AM +0100, David Hildenbrand wrote: >> A while ago I talked with Peter about an extended uffd (here: WP) >> mechanism that would work on fds instead of the process address space. > > As far as I can tell, uffd is a grotesque hack that exists to work around > the poor choice to use anonymous memory instead of file-backed memory > in kvm. Every time I see somebody mention it, I feel pain. > I might be missing something important, because KVM can deal with file-back memory just fine and uffd is used heavily outside of hypervisors. I'd love to learn how to handle what ordinary uffd (handle missing/unpopulated pages) and uffd-wp (handle write access to pages) can do with files instead. Because if something like that already exists, it would be precisely what I am talking about. Maybe mentioning uffd was a bad choice ;) -- Thanks, David / dhildenb