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 D4B7EC433FE for ; Mon, 11 Apr 2022 19:08:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2C5CD6B0072; Mon, 11 Apr 2022 15:08:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 273CE6B0073; Mon, 11 Apr 2022 15:08:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 13B086B0074; Mon, 11 Apr 2022 15:08:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0202.hostedemail.com [216.40.44.202]) by kanga.kvack.org (Postfix) with ESMTP id 044666B0072 for ; Mon, 11 Apr 2022 15:08:52 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id AE6A4A7C33 for ; Mon, 11 Apr 2022 19:08:51 +0000 (UTC) X-FDA: 79345535262.28.BEACE85 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf16.hostedemail.com (Postfix) with ESMTP id A59C0180005 for ; Mon, 11 Apr 2022 19:08:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=e1fwTBXjpGLJFVbGSqSy8bq2chVaIHZsuFHQZUO8y+E=; b=mmM2y6S6rZIMBTjXkY4V46NlM0 H5kyclJL/93EdWx7Zwa9CDDPoqGca8SYxp0BdNUZ4v8CCNUA9UAvFXNgS6FE22UO+nXuxfcCyzxa6 UJeLsjlNW2tgw6U745WHagYGxBFWwKenSW7WYS1DaID+825/M+lQ5Tg/XpTwDYyJRDujcDqcUGbRP P3R3ZotqUwp3eoZPX1KgB8vRrCkHohmK3+VMa8ZmG44pp7W9l+I6Rfu6W0YI1DVW7b7HZL2dJ1vf1 wyCT2pu99/McoU6vEd7DL7rA14VRz4niYl+IQat9J7XlEDRAYdLD8S3ID5AuSHaZDPKozB6PG2Nba AMH9lpEQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1ndzOK-00Cart-EG; Mon, 11 Apr 2022 19:08:00 +0000 Date: Mon, 11 Apr 2022 20:08:00 +0100 From: Matthew Wilcox To: Dave Hansen Cc: Khalid Aziz , akpm@linux-foundation.org, 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 Subject: Re: [PATCH v1 00/14] Add support for shared PTEs across processes Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=mmM2y6S6; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A59C0180005 X-Stat-Signature: si1jr5ysdcnkssmxzw9t6k1mbfiomyi9 X-HE-Tag: 1649704130-138904 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 Mon, Apr 11, 2022 at 11:51:46AM -0700, Dave Hansen wrote: > On 4/11/22 10:37, Matthew Wilcox wrote: > > Another argument that MM developers find compelling is that we can reduce > > some of the complexity in hugetlbfs where it has the ability to share > > page tables between processes. > > When could this complexity reduction actually happen in practice? Can > this mshare thingy be somehow dropped in underneath the existing > hugetlbfs implementation? Or would userspace need to change? Userspace needs to opt in to mshare, so there's going to be a transition period where we still need hugetlbfs to still support it, but I have the impression that the users that need page table sharing are pretty specialised and we'll be able to find them all before disabling it. I don't think we can make it transparent to userspace, but I'll noodle on that a bit.