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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04F22C0015E for ; Tue, 1 Aug 2023 19:28:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232404AbjHAT2J (ORCPT ); Tue, 1 Aug 2023 15:28:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55004 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231786AbjHAT2G (ORCPT ); Tue, 1 Aug 2023 15:28:06 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D5C3F10E; Tue, 1 Aug 2023 12:28:05 -0700 (PDT) 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=gaut94wtJvcD0zi3q7k4JYT7+QEi/Ua5L41+y8I+W9A=; b=FWrX0z28U3EqiQJrIFfM/btNnD h0r6Q0OJ3rp5KMXJorNilcAfp8f3kEIhltT8RjmJWCxZ+EUksczMNZPOLsVqYa8HvYCGAKxjvRc6Z ZHXdgNjBBXysu78uR2VE4uvd/UnmJTUo3BNeWLgbqgStaLTfK4lAPj83qDQEU85kHEyUSozuXFVlJ y1i8KQOzRWSaUDKfxEWBhsPHwkBEDJQPlrogyIqDoeihbK6N8zE1PqhZkxC3zwUdvdzanaPkJK5nq VdvR8Yc4tHO6vQgiV2CjJtdAth0lqVMHIYcwyP+9RxH1FNA2UhNOA8i99+Whl9iPkLdc/nlZ850V3 puAflRfA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qQv2I-00AacX-ID; Tue, 01 Aug 2023 19:28:02 +0000 Date: Tue, 1 Aug 2023 20:28:02 +0100 From: Matthew Wilcox To: Rongwei Wang Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, "xuyu@linux.alibaba.com" Subject: Re: [PATCH RFC v2 0/4] Add support for sharing page tables across processes (Previously mshare) Message-ID: References: <74fe50d9-9be9-cc97-e550-3ca30aebfd13@linux.alibaba.com> <9faea1cf-d3da-47ff-eb41-adc5bd73e5ca@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 01, 2023 at 02:53:02PM +0800, Rongwei Wang wrote: > > On 2023/8/1 00:38, Matthew Wilcox wrote: > > On Mon, Jul 31, 2023 at 06:30:22PM +0200, David Hildenbrand wrote: > > > Assume we do do the page table sharing at mmap time, if the flags are right. > > > Let's focus on the most common: > > > > > > mmap(memfd, PROT_READ | PROT_WRITE, MAP_SHARED) > > > > > > And doing the same in each and every process. > > That may be the most common in your usage, but for a database, you're > > looking at two usage scenarios. Postgres calls mmap() on the database > > file itself so that all processes share the kernel page cache. > > Some Commercial Databases call mmap() on a hugetlbfs file so that all > > processes share the same userspace buffer cache. Other Commecial > > Databases call shmget() / shmat() with SHM_HUGETLB for the exact > > same reason. > > > > This is why I proposed mshare(). Anyone can use it for anything. > > Hi Matthew > > I'm a little confused about this mshare(). Which one is the mshare() you > refer to here, previous mshare() based on filesystem or this RFC v2 posted > by Khalid? > > IMHO, they have much difference between previously mshare() and > MAP_SHARED_PT now. I haven't read this version of the patchset. I'm describing the original idea, not what it may have turned into. As far as I'm concerned, we're still trying to decide what functionality we actually want, not arguing about whether this exact patchset has the correct number of tab indents to be merged.