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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id c14sm15931537qta.80.2019.10.23.22.33.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Oct 2019 22:33:02 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo Date: Thu, 24 Oct 2019 01:33:01 -0400 Message-Id: <4D23D83F-190F-40B3-9EB9-C167642321B2@lca.pw> References: <20191023153040.c7fff4bc7c86ed605fc4667f@linux-foundation.org> Cc: Waiman Long , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner , Michal Hocko , Roman Gushchin , Vlastimil Babka , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini In-Reply-To: <20191023153040.c7fff4bc7c86ed605fc4667f@linux-foundation.org> To: Andrew Morton X-Mailer: iPhone Mail (17A878) 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 Oct 23, 2019, at 6:30 PM, Andrew Morton wro= te: >=20 > Yes, removing things is hard. One approach is to add printk_once(this > is going away, please email us if you use it) then wait a few years.=20 > Backport that one-liner into -stable kernels to hopefully speed up the > process. Although it still look like an overkill to me given, 1) Mel given a green light to remove it. 2) Nobody justifies any sensible reason to keep it apart from it was probabl= y only triggering by some testing tools blindly read procfs entries. it is still better than wasting developers=E2=80=99 time to beating the =E2=80= =9Cdead=E2=80=9D horse. >=20 > Meanwhile, we need to fix the DoS opportunity. How about my suggestion > that we limit the count to 1024, see if anyone notices? I bet they > don't! The DoS is probably there since the file had been introduced almost 10 year= s ago, so I suspect it is not that easily exploitable.=