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From: Roman Gushchin To: Waiman Long Cc: Michal Hocko , Tejun Heo , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Jonathan Corbet , Shakeel Butt , Muchun Song , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, Peter Hunt Subject: Re: [RFC PATCH] mm, memcg: introduce memory.high.throttle Message-ID: References: <20250129191204.368199-1-longman@redhat.com> <211b394b-3b9a-4872-8c07-b185386487d3@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <211b394b-3b9a-4872-8c07-b185386487d3@redhat.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: D04574001A X-Stat-Signature: if1r34get5wmujqufps5n3yg1wpny6af X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1738256735-329317 X-HE-Meta: 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 YB+u4Vx1 Li3cjDqg5MUm9BNsPHgnZQYhn4ad4RcEisiy6gDAiotI9zc4MjRolOoFZPH7RwVVh4APzRwfyznbhihr//tjZ6o17sHfkVijEMwqISIn83Wz6quY+Rh03xEsKwhqxyAUjF2qsV3vqOL8Uwrr33pCxbUpGLluXdL4WcLs6vMbE+5hBVDctGYBI6EGriOWHamzk7yCBIZgwKFf4HWomAf0WBJDE6Q== 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: List-Subscribe: List-Unsubscribe: On Thu, Jan 30, 2025 at 10:05:34AM -0500, Waiman Long wrote: > On 1/30/25 3:15 AM, Michal Hocko wrote: > > On Wed 29-01-25 14:12:04, Waiman Long wrote: > > > Since commit 0e4b01df8659 ("mm, memcg: throttle allocators when failing > > > reclaim over memory.high"), the amount of allocator throttling had > > > increased substantially. As a result, it could be difficult for a > > > misbehaving application that consumes increasing amount of memory from > > > being OOM-killed if memory.high is set. Instead, the application may > > > just be crawling along holding close to the allowed memory.high memory > > > for the current memory cgroup for a very long time especially those > > > that do a lot of memcg charging and uncharging operations. > > > > > > This behavior makes the upstream Kubernetes community hesitate to > > > use memory.high. Instead, they use only memory.max for memory control > > > similar to what is being done for cgroup v1 [1]. > > Why is this a problem for them? > My understanding is that a mishaving container will hold up memory.high > amount of memory for a long time instead of getting OOM killed sooner and be > more productively used elsewhere. > > > > > To allow better control of the amount of throttling and hence the > > > speed that a misbehving task can be OOM killed, a new single-value > > > memory.high.throttle control file is now added. The allowable range > > > is 0-32. By default, it has a value of 0 which means maximum throttling > > > like before. Any non-zero positive value represents the corresponding > > > power of 2 reduction of throttling and makes OOM kills easier to happen. > > I do not like the interface to be honest. It exposes an implementation > > detail and casts it into a user API. If we ever need to change the way > > how the throttling is implemented this will stand in the way because > > there will be applications depending on a behavior they were carefuly > > tuned to. > > > > It is also not entirely sure how is this supposed to be used in > > practice? How do people what kind of value they should use? > Yes, I agree that a user may need to run some trial runs to find a proper > value. Perhaps a simpler binary interface of "off" and "on" may be easier to > understand and use. > > > > > System administrators can now use this parameter to determine how easy > > > they want OOM kills to happen for applications that tend to consume > > > a lot of memory without the need to run a special userspace memory > > > management tool to monitor memory consumption when memory.high is set. > > Why cannot they achieve the same with the existing events/metrics we > > already do provide? Most notably PSI which is properly accounted when > > a task is throttled due to memory.high throttling. > > That will require the use of a userspace management agent that looks for > these stalling conditions and make the kill, if necessary. There are > certainly users out there that want to get some benefit of using memory.high > like early memory reclaim without the trouble of handling these kind of > stalling conditions. So you basically want to force the workload into some sort of a proactive reclaim but without an artificial slow down? It makes some sense to me, but 1) Idk if it deserves a new API, because it can be relatively easy implemented in userspace by a daemon which monitors cgroups usage and reclaims the memory if necessarily. No kernel changes are needed. 2) If new API is introduced, I think it's better to introduce a new limit, e.g. memory.target, keeping memory.high semantics intact. Thanks!