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(p200300cbc70f80009797008f1ed97596.dip0.t-ipconnect.de. [2003:cb:c70f:8000:9797:8f:1ed9:7596]) by smtp.gmail.com with ESMTPSA id o11sm8214857edq.5.2022.01.25.05.19.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Jan 2022 05:19:03 -0800 (PST) Message-ID: Date: Tue, 25 Jan 2022 14:18:57 +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: William Kucharski , "Kirill A. Shutemov" Cc: Khalid Aziz , akpm@linux-foundation.org, willy@infradead.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 References: <20220125114212.ks2qtncaahi6foan@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-Stat-Signature: ju3th9f7ayjh1dn1ij3xbzihityqs4zn X-Rspam-User: nil Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=K5zPPOJI; spf=none (imf14.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A6C6F100082 X-HE-Tag: 1643116749-817051 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 25.01.22 13:09, William Kucharski wrote: > I would think this should be the case; certainly it seems to be a more effective approach than having to manually enable sharing via the API in every case or via changes to ld.so. > > If anything it might be useful to have an API for shutting it off, though there are already multiple areas where the system shares resources in ways that cannot be shut off by user action. > I don't have time to look into details right now, but I see various possible hard-to-handle issues with sharing anon pages via this mechanism between processes. If we could restrict it to MAP_SHARED and have some magic toggle to opt in, that would be great. Features like uffd that we might soon see on some MAP_SHARED pages will require to not share page tables automatically I assume. -- Thanks, David / dhildenb