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 B6560C433EF for ; Tue, 25 Jan 2022 19:00:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 27DA96B0074; Tue, 25 Jan 2022 14:00:16 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 22C416B007B; Tue, 25 Jan 2022 14:00:16 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0F4616B007D; Tue, 25 Jan 2022 14:00:16 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0099.hostedemail.com [216.40.44.99]) by kanga.kvack.org (Postfix) with ESMTP id F26496B0074 for ; Tue, 25 Jan 2022 14:00:15 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id C329293D6E for ; Tue, 25 Jan 2022 19:00:15 +0000 (UTC) X-FDA: 79069724790.14.7FF5429 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf16.hostedemail.com (Postfix) with ESMTP id 244AA180014 for ; Tue, 25 Jan 2022 19:00:14 +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=bt8DG4kv/HiKHmCxuEq4ti3BrhnQMbSnttO4/8+9Xs4=; b=sl1vLhCyZd3T8KmPTjKxZcrVsT yHbYNZfD0SvdklJb+XFTy6+SRgqlug+6n3hTafjWom8+t6HNsM/kinSWuwgRZCUGLx7tIXmxgA+dU vCS89F3ztYMaw23a4R+qztj+agAyg0rwnXi1SOlME1Uu2GQA1EKzIQhX9cg3e22vquRlV3ICyETMj 9kV9sCClzEc7Y+vM9ym4CDlTO49jmrIVLe6IwTczO8MrQLT/+dYnmi7pF9mGBTRCiA3IqfrJ0lWAI SwpoxqO/d8GcivW55uKjW00PHVJ83rpOncMgm1/HcBGxHsoNe+P5b79TCmqADb1hL4bY20Cuiu5+p OJsyB/XA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCR2k-003GLD-An; Tue, 25 Jan 2022 18:59:50 +0000 Date: Tue, 25 Jan 2022 18:59:50 +0000 From: Matthew Wilcox To: "Kirill A. Shutemov" Cc: Khalid Aziz , akpm@linux-foundation.org, longpeng2@huawei.com, arnd@arndb.de, dave.hansen@linux.intel.com, david@redhat.com, rppt@kernel.org, surenb@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH 0/6] Add support for shared PTEs across processes Message-ID: References: <20220125114212.ks2qtncaahi6foan@box.shutemov.name> <20220125135917.ezi6itozrchsdcxg@box.shutemov.name> <20220125185705.wf7p2l77vggipfry@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220125185705.wf7p2l77vggipfry@box.shutemov.name> Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=sl1vLhCy; 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-Rspam-User: nil X-Rspamd-Queue-Id: 244AA180014 X-Stat-Signature: myqg8kduzazzik8jr9fdhbdue587cku6 X-Rspamd-Server: rspam12 X-HE-Tag: 1643137214-29376 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000073, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jan 25, 2022 at 09:57:05PM +0300, Kirill A. Shutemov wrote: > On Tue, Jan 25, 2022 at 02:09:47PM +0000, Matthew Wilcox wrote: > > > I think zero-API approach (plus madvise() hints to tweak it) is worth > > > considering. > > > > I think the zero-API approach actually misses out on a lot of > > possibilities that the mshare() approach offers. For example, mshare() > > allows you to mmap() many small files in the shared region -- you > > can't do that with zeroAPI. > > Do you consider a use-case for many small files to be common? I would > think that the main consumer of the feature to be mmap of huge files. > And in this case zero enabling burden on userspace side sounds like a > sweet deal. mmap() of huge files is certainly the Oracle use-case. With occasional funny business like mprotect() of a single page in the middle of a 1GB hugepage. The approach of designating ranges of a process's address space as sharable with other processes felt like the cleaner & frankly more interesting approach that opens up use-cases other than "hurr, durr, we are Oracle, we like big files, kernel get out of way now, transactions to perform".