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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5226CC3567B for ; Thu, 27 Feb 2020 17:23:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3481121D7E for ; Thu, 27 Feb 2020 17:23:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729697AbgB0RXE (ORCPT ); Thu, 27 Feb 2020 12:23:04 -0500 Received: from ale.deltatee.com ([207.54.116.67]:56590 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728413AbgB0RXD (ORCPT ); Thu, 27 Feb 2020 12:23:03 -0500 Received: from s0106ac1f6bb1ecac.cg.shawcable.net ([70.73.163.230] helo=[192.168.11.155]) by ale.deltatee.com with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1j7MrE-0003nL-Q0; Thu, 27 Feb 2020 10:21:57 -0700 To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-mm@kvack.org, Dan Williams , Michal Hocko , David Hildenbrand , Andrew Morton , Christoph Hellwig , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Eric Badger References: <20200221182503.28317-1-logang@deltatee.com> <20200227171704.GK31668@ziepe.ca> From: Logan Gunthorpe Message-ID: Date: Thu, 27 Feb 2020 10:21:50 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200227171704.GK31668@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 70.73.163.230 X-SA-Exim-Rcpt-To: ebadger@gigaio.com, peterz@infradead.org, luto@kernel.org, dave.hansen@linux.intel.com, bp@alien8.de, mingo@redhat.com, tglx@linutronix.de, benh@kernel.crashing.org, will@kernel.org, catalin.marinas@arm.com, hch@lst.de, akpm@linux-foundation.org, david@redhat.com, mhocko@kernel.org, dan.j.williams@intel.com, linux-mm@kvack.org, platform-driver-x86@vger.kernel.org, linux-sh@vger.kernel.org, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-ia64@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v3 0/7] Allow setting caching mode in arch_add_memory() for P2PDMA X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-02-27 10:17 a.m., Jason Gunthorpe wrote: >> Instead of this, this series proposes a change to arch_add_memory() >> to take the pgprot required by the mapping which allows us to >> explicitly set pagetable entries for P2PDMA memory to WC. > > Is there a particular reason why WC was selected here? I thought for > the p2pdma cases there was no kernel user that touched the memory? Yes, that's correct. I choose WC here because the existing users are registering memory blocks without side effects which fit the WC semantics well. > I definitely forsee devices where we want UC instead. Yes. My expectation is that once we have a kernel user that needs this, we'd wire the option through struct dev_pagemap so the caller can choose the mapping that makes sense. Logan