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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id u7sm1494346qkj.113.2019.08.29.11.44.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Aug 2019 11:44:03 -0700 (PDT) Message-ID: <1567104241.5576.30.camel@lca.pw> Subject: Re: [PATCH 00/10] OOM Debug print selection and additional information From: Qian Cai To: Edward Chron Cc: Michal Hocko , Tetsuo Handa , Andrew Morton , Roman Gushchin , Johannes Weiner , David Rientjes , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ivan Delalande Date: Thu, 29 Aug 2019 14:44:01 -0400 In-Reply-To: References: <20190826193638.6638-1-echron@arista.com> <20190827071523.GR7538@dhcp22.suse.cz> <20190828065955.GB7386@dhcp22.suse.cz> <20190829071105.GQ28313@dhcp22.suse.cz> <297cf049-d92e-f13a-1386-403553d86401@i-love.sakura.ne.jp> <20190829115608.GD28313@dhcp22.suse.cz> <1567093344.5576.23.camel@lca.pw> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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 Thu, 2019-08-29 at 09:09 -0700, Edward Chron wrote: > > Feel like you are going in circles to "sell" without any new informat= ion. If > > you > > need to deal with OOM that often, it might also worth working with FB= on > > oomd. > >=20 > > https://github.com/facebookincubator/oomd > >=20 > > It is well-known that kernel OOM could be slow and painful to deal wi= th, so > > I > > don't buy-in the argument that kernel OOM recover is better/faster th= an a > > kdump > > reboot. > >=20 > > It is not unusual that when the system is triggering a kernel OOM, it= is > > almost > > trashed/dead. Although developers are working hard to improve the rec= overy > > after > > OOM, there are still many error-paths that are not going to survive w= hich > > would > > leak memories, introduce undefined behaviors, corrupt memory etc. >=20 > But as you have pointed out many people are happy with current OOM proc= essing > which is the report and recovery so for those people a kdump reboot is > overkill. > Making the OOM report at least optionally a bit more informative has va= lue. > Also > making sure it doesn't produce excessive output is desirable. >=20 > I do agree for developers having to have all the system state a kdump > provides that > and as long as you can reproduce the OOM event that works well. But > that is not the > common case as has already been discussed. >=20 > Also, OOM events that are due to kernel bugs could leak memory and over= time > and cause a crash, true. But that is not what we typically see. In > fact we've had > customers come back and report issues on systems that have been in cont= inuous > operation for years. No point in crashing their system. Linux if > properly maintained > is thankfully quite stable. But OOMs do happen and root causing them to > prevent > future occurrences is desired. This is not what I meant. After an OOM event happens, many kernel memory allocations could fail.=C2=A0Since very few people are testing those erro= r-paths due to allocation failures, it is considered one of those most buggy areas in= the kernel. Developers have mostly been focus on making sure the kernel OOM s= hould not happen in the first place. I still think the time is better spending on improving things like eBPF, = oomd and kdump etc to solve your problem, but leave the kernel OOM report code= alone.