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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id 8sm11519536qkm.92.2020.01.27.21.48.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jan 2020 21:48:30 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers Date: Tue, 28 Jan 2020 00:48:30 -0500 Message-Id: References: <012158b7-a40e-050f-cd1b-d6ce7faf042f@arm.com> Cc: Linux-MM , Andrew Morton , Vlastimil Babka , Greg Kroah-Hartman , Thomas Gleixner , Mike Rapoport , Jason Gunthorpe , Dan Williams , Peter Zijlstra , Michal Hocko , Mark Rutland , Mark Brown , Steven Price , Ard Biesheuvel , Masahiro Yamada , Kees Cook , Tetsuo Handa , Matthew Wilcox , Sri Krishna chowdary , Dave Hansen , Russell King - ARM Linux , Michael Ellerman , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Vineet Gupta , James Hogan , Paul Burton , Ralf Baechle , "Kirill A . Shutemov" , Gerald Schaefer , Christophe Leroy , Ingo Molnar , linux-snps-arc@lists.infradead.org, linux-mips@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, sparclinux@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <012158b7-a40e-050f-cd1b-d6ce7faf042f@arm.com> To: Anshuman Khandual X-Mailer: iPhone Mail (17C54) 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 Jan 27, 2020, at 11:58 PM, Anshuman Khandual wrote: >=20 > As I had mentioned before, the test attempts to formalize page table helpe= r semantics > as expected from generic MM code paths and intend to catch deviations when= enabled on > a given platform. How else should we test semantics errors otherwise ? The= re are past > examples of usefulness for this procedure on arm64 and on s390. I am wonde= ring how > else to prove the usefulness of a debug feature if these references are no= t enough. Not saying it will not be useful. As you mentioned it actually found a bug o= r two in the past. The problem is that there is always a cost to maintain so= mething like this, and nobody knew how things could be broken even for the i= solated code you mentioned in the future given how complicated the kernel co= de base is. I am not so positive that many developers would enable this debu= g feature and use it on a regular basis from the information you gave so far= .=20 On the other hand, it might just be good at maintaining this thing out of tr= ee by yourself anyway, because if there isn=E2=80=99t going to be used by ma= ny developers, few people is going to contribute to this and even noticed wh= en it is broken. What=E2=80=99s the point of getting this merged apart from b= eing getting some meaningless credits?=