From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3155C433F5 for ; Mon, 11 Apr 2022 18:47:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 268366B0072; Mon, 11 Apr 2022 14:47:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 216B96B0073; Mon, 11 Apr 2022 14:47:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 091C16B0074; Mon, 11 Apr 2022 14:47:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id E9B026B0072 for ; Mon, 11 Apr 2022 14:47:19 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id A94B01D84 for ; Mon, 11 Apr 2022 18:47:19 +0000 (UTC) X-FDA: 79345480998.04.0E40D8F Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by imf01.hostedemail.com (Postfix) with ESMTP id F1A0540008 for ; Mon, 11 Apr 2022 18:47:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1649702839; x=1681238839; h=message-id:date:mime-version:to:cc:references:from: subject:in-reply-to:content-transfer-encoding; bh=BlRY1ucylwTHwi1CNLdV5Rmu+hVaqB1rWV9jwjmzSX0=; b=jQAuapVNGh9TW8+n6znCAT4RX1l1ve0FRxzsMwyraLWyyV3sZ36Jy0Ql TbbUN/XrY1VbzER/48e2/BelI1HAuEoKEDl0pE+wBJB0qqpgx8Fofv0tw ZVntwZfbcOp2CQIpnzlJJt0osPgcwrnEm94+EmwU3GLbT3bxqOzX4nVLZ yIUDBFI3yiiW3pZD0xFy1SoX3ZlLnBx+8ci7QGrHj95OzAyf1KvEWV596 Yk0zC0fmvVcZvTWzlxwRkLBhJSqFWpCtS154qBzjWDJ4AY6l9Yewm9ue3 2f8eK5Y9W0Fj+BX+HSDLy9+wssOUL6MGjW0xmWQUmNO3y+JUIW2I9xTPK A==; X-IronPort-AV: E=McAfee;i="6400,9594,10314"; a="242776249" X-IronPort-AV: E=Sophos;i="5.90,252,1643702400"; d="scan'208";a="242776249" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Apr 2022 11:47:17 -0700 X-IronPort-AV: E=Sophos;i="5.90,252,1643702400"; d="scan'208";a="572338003" Received: from minhjohn-mobl.amr.corp.intel.com (HELO [10.212.44.201]) ([10.212.44.201]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Apr 2022 11:47:15 -0700 Message-ID: Date: Mon, 11 Apr 2022 11:47:20 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Content-Language: en-US To: Khalid Aziz , akpm@linux-foundation.org, willy@infradead.org Cc: aneesh.kumar@linux.ibm.com, arnd@arndb.de, 21cnbao@gmail.com, corbet@lwn.net, dave.hansen@linux.intel.com, david@redhat.com, ebiederm@xmission.com, hagen@jauu.net, jack@suse.cz, keescook@chromium.org, kirill@shutemov.name, kucharsk@gmail.com, linkinjeon@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, longpeng2@huawei.com, luto@kernel.org, markhemm@googlemail.com, pcc@google.com, rppt@kernel.org, sieberf@amazon.com, sjpark@amazon.de, surenb@google.com, tst@schoebel-theuer.de, yzaikin@google.com References: From: Dave Hansen Subject: Re: [PATCH v1 00/14] Add support for shared PTEs across processes In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 1o4gdta55s1b7d85oeudsokc6r5tk1j4 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: F1A0540008 Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=jQAuapVN; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf01.hostedemail.com: domain of dave.hansen@intel.com has no SPF policy when checking 192.55.52.151) smtp.mailfrom=dave.hansen@intel.com X-Rspam-User: X-HE-Tag: 1649702838-51202 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 4/11/22 09:05, Khalid Aziz wrote: > PTEs are shared at pgdir level and hence it imposes following > requirements on the address and size given to the mshare(): > > - Starting address must be aligned to pgdir size (512GB on x86_64). > This alignment value can be looked up in /proc/sys/vm//mshare_size > - Size must be a multiple of pgdir size > - Any mappings created in this address range at any time become > shared automatically > - Shared address range can have unmapped addresses in it. Any access > to unmapped address will result in SIGBUS > > Mappings within this address range behave as if they were shared > between threads, so a write to a MAP_PRIVATE mapping will create a > page which is shared between all the sharers. The first process that > declares an address range mshare'd can continue to map objects in > the shared area. All other processes that want mshare'd access to > this memory area can do so by calling mshare(). After this call, the > address range given by mshare becomes a shared range in its address > space. Anonymous mappings will be shared and not COWed. What does this mean in practice?