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[109.81.85.139]) by smtp.gmail.com with UTF8SMTPSA id a640c23a62f3a-adec892b90csm81370566b.142.2025.06.13.00.05.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Jun 2025 00:05:14 -0700 (PDT) Date: Fri, 13 Jun 2025 09:05:13 +0200 From: Michal Hocko To: Zihuan Zhang Cc: David Hildenbrand , Peter Zijlstra , rafael@kernel.org, len.brown@intel.com, pavel@kernel.org, kees@kernel.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH] PM: Optionally block user fork during freeze to improve performance Message-ID: References: <20250606062502.19607-1-zhangzihuan@kylinos.cn> <20250606082244.GL30486@noisy.programming.kicks-ass.net> <83513599-e007-4d07-ac28-386bc5c7552d@kylinos.cn> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri 13-06-25 10:37:42, Zihuan Zhang wrote: > Hi David, > Thanks for your advice! > > 在 2025/6/10 18:50, David Hildenbrand 写道: > > 　　　 　 　 　　 　 　 　 　 　 　 　 　 　 　　 > > Can't this problem be mitigated by simply not scheduling the new fork'ed > > process while the system is frozen? > > > > Or what exact scenario are you worried about? > > Let me revisit the core issue for clarity. Under normal conditions, most > processes in the system are in a sleep state, and only a few are runnable. > So even with thousands of processes, the freezer generally works reliably > and completes within a reasonable time How do you define reasonable time? > However, in our fork-based test scenario, we observed repeated freeze > retries. Does this represent any real life scenario that happens on your system? In other words how often do you miss your "reasonable time" treshold while running a regular workload. Does the freezer ever fail? [...] > You’re right — blocking fork() is quite intrusive, so it’s worth exploring > alternatives. We’ll try implementing your idea of preventing the newly > forked process from being scheduled while the system is freezing, rather > than failing the fork() call outright. Just curious, are you interested in global freezer only or is the cgroup freezer involved as well? -- Michal Hocko SUSE Labs