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Thu, 02 Mar 2023 02:18:33 -0800 (PST) X-Google-Smtp-Source: AK7set/uxV1v23Oh/sg3P74SBCZjjX//Q96d/fEGultmNCbYhqze+hDU7mOVq32IblaxwcWQxNVqMQ== X-Received: by 2002:a5d:558d:0:b0:2c7:694:aa18 with SMTP id i13-20020a5d558d000000b002c70694aa18mr6612409wrv.15.1677752313305; Thu, 02 Mar 2023 02:18:33 -0800 (PST) Received: from vschneid.remote.csb ([154.57.232.159]) by smtp.gmail.com with ESMTPSA id b6-20020a5d4d86000000b002ca864b807csm12635217wru.0.2023.03.02.02.18.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Mar 2023 02:18:32 -0800 (PST) From: Valentin Schneider To: Michal Hocko Cc: Sebastian Andrzej Siewior , cgroups@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Michal =?utf-8?Q?Koutn=C3=BD?= , Peter Zijlstra , Thomas Gleixner , Vladimir Davydov , Waiman Long , Roman Gushchin , Shakeel Butt Subject: Re: [PATCH v5 2/6] mm/memcg: Disable threshold event handlers on PREEMPT_RT In-Reply-To: References: <20220226204144.1008339-1-bigeasy@linutronix.de> <20220226204144.1008339-3-bigeasy@linutronix.de> Date: Thu, 02 Mar 2023 10:18:31 +0000 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 77373140005 X-Stat-Signature: cn6wmesehem48kc3sg78bsseu3cc3qd1 X-Rspam-User: X-HE-Tag: 1677752316-704566 X-HE-Meta: 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 iIa8eWZb P2e+CbUawhVtB5EWNmSSWCb9OmkfLAzCxkqdXCDxysPOewiWG14ZbYifOjk3YOydUfG0NetoLrHqH32fAX9FnjQPBvjAmQaNdafqcEqE14YWI95vXlOL1AGYDDxP/NyDXDAUkANBaIx6NxAV65gkTe5LNisvJQI75raZO4Fv4pANqZ4oPvnUfTbQJeTO3W0Y/ovtYMsCEQLQdaiCyDUMHNj9tx2jiCOhutIWvqbWTRLv1jDBV1hzEd+8ml3UIyZrHM/NE4dU7OXyJ5OA7IR8bWyTPPhAn1e8QxQE+BfYJXIJZPhE2PNRkI+YGbSKbtpfuhAS2YxYR99uqYwG+SOY2TzxUE+W362R5+kuVbSNH7cp1Ic0NBN0Ql1bWg4KK7hHb3nI4Qt4UNGWR0UXTNC8urgP1I7WvB1UHUFxt X-Bogosity: Ham, tests=bogofilter, spamicity=0.000049, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02/03/23 08:45, Michal Hocko wrote: > On Wed 01-03-23 18:23:19, Valentin Schneider wrote: >> On 26/02/22 21:41, Sebastian Andrzej Siewior wrote: >> > During the integration of PREEMPT_RT support, the code flow around >> > memcg_check_events() resulted in `twisted code'. Moving the code around >> > and avoiding then would then lead to an additional local-irq-save >> > section within memcg_check_events(). While looking better, it adds a >> > local-irq-save section to code flow which is usually within an >> > local-irq-off block on non-PREEMPT_RT configurations. >> > >> >> Hey, sorry for necro'ing a year-old thread - would you happen to remember >> what the issues were with memcg_check_events()? I ran tests against >> cgroupv1 using an eventfd on OOM with the usual debug arsenal and didn't >> detect anything, I'm guessing it has to do with the IRQ-off region >> memcg_check_events() is called from? > > I would have to look into details but IIRC the resulting code to make > the code RT safe was dreaded and hard to maintain as a result. As we > didn't really have any real life usecase, disabling the code was an > easier way to go forward. So it is not the code would be impossible to > be enabled for RT it just doeasn't seam to be worth all the complexity. > Right, thanks for having a look. >> I want cgroupv1 to die as much as the next person, but in that specific >> situation I kinda need cgroupv1 to behave somewhat sanely on RT with >> threshold events :/ > > Could you expand on the usecase? > In this case it's just some middleware leveraging memcontrol cgroups and setting up callbacks for in-cgroup OOM events. This is a supported feature in cgroupv2, so this isn't a problem of cgroupv1 vs cgroupv2 feature parity, but rather one of being in a transitional phase where the middleware itself hasn't fully migrated to using cgroupv2. > -- > Michal Hocko > SUSE Labs