From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 29 Jan 2020 10:36:40 +0000 From: Catalin Marinas Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers Message-ID: <20200129103640.GA668562@arrakis.emea.arm.com> References: <20200128174709.GK655507@arrakis.emea.arm.com> <69091BA4-18C4-4425-A5E2-31FBE4654AF9@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69091BA4-18C4-4425-A5E2-31FBE4654AF9@lca.pw> Sender: linux-kernel-owner@vger.kernel.org List-ID: To: Qian Cai Cc: Mark Rutland , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , James Hogan , Heiko Carstens , Michal Hocko , linux-mm@kvack.org, Paul Mackerras , sparclinux@vger.kernel.org, Ingo Molnar , linux-s390@vger.kernel.org, Jason Gunthorpe , Michael Ellerman , Vlastimil Babka , x86@kernel.org, Russell King - ARM Linux , Matthew Wilcox , Steven Price , Tetsuo Handa , linux-arm-kernel@lists.infradead.org, linux-snps-arc@lists.infradead.org, Kees Cook , Anshuman Khandual , Masahiro Yamada , Dan Williams , Mark Brown , "Kirill A . Shutemov" , Thomas Gleixner , Gerald Schaefer , Christophe Leroy , Sri Krishna chowdary , Dave Hansen , Greg Kroah-Hartman , Ard Biesheuvel , linux-mips@vger.kernel.org, Ralf Baechle , linux-kernel@vger.kernel.org, Paul Burton , Mike Rapoport , Vineet Gupta , Martin Schwidefsky , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" On Tue, Jan 28, 2020 at 02:07:10PM -0500, Qian Cai wrote: > On Jan 28, 2020, at 12:47 PM, Catalin Marinas wrote: > > The primary goal here is not finding regressions but having clearly > > defined semantics of the page table accessors across architectures. x86 > > and arm64 are a good starting point and other architectures will be > > enabled as they are aligned to the same semantics. > > This still does not answer the fundamental question. If this test is > simply inefficient to find bugs, Who said this is inefficient (other than you)? > who wants to spend time to use it regularly? Arch maintainers, mm maintainers introducing new macros or assuming certain new semantics of the existing macros. > If this is just one off test that may get running once in a few years > (when introducing a new arch), how does it justify the ongoing cost to > maintain it? You are really missing the point. It's not only for a new arch but changes to existing arch code. And if the arch code churn in this area is relatively small, I'd expect a similarly small cost of maintaining this test. If you only turn DEBUG_VM on once every few years, don't generalise this to the rest of the kernel developers (as others pointed out, this test is default y if DEBUG_VM). Anyway, I think that's a pointless discussion, so not going to reply further (unless you have technical content to add). -- Catalin